The Wildlife–Livestock Interface as a Bidirectional Pathway for the Spread of ESBL-Producing Escherichia coli

1. Introduction

Antimicrobial resistance (AMR) is a global problem that must be combated with a comprehensive "One Health" approach [1,2,3]. Infections caused by multidrug-resistant (MDR) bacteria have become a global health challenge.

Bacteria can transfer resistance genes horizontally, including between different species. The set of genes that confer resistance to one or more antibiotic families ("resistome") can be transferred between pathogenic and non-pathogenic bacteria in humans and animals (both domestic and wild), as well as with environmental bacteria [4,5,6]. This evolution toward multidrug resistance is the result of complex bacterial events involving mutations and gene transfers between species via mobile elements [7]. The increasing prevalence of MDR or extensively drug-resistant (XDR) bacteria reinforces the need to develop surveillance studies to detect and control these strains [8].

As indicated in the "WHO - Global Action Plan on Antimicrobial Resistance" [9], this problem represents a drain on the global economy, with economic losses due to reduced productivity caused by diseases (in both humans and animals) and increased treatment costs. Although not explicitly mentioned, it is clear that the increase in antibiotic resistance affects the achievement of sustainable development goals (SDGs). The increase in animal infections caused by antibiotic-resistant bacteria makes it difficult to build sustainable food production systems and, therefore, hinders the SDGs on health, poverty, food security and economic growth [10].

Wildlife has been identified as a driver of the spread of genes conferring resistance to clinically important antimicrobials [11,12,13]. Although theoretically wild animals are not exposed to clinically relevant antibiotics, the detection of MDR strains in wildlife is increasing considerably, reinforcing the need for studies focused on this issue [14,15]. Furthermore, monitoring these bacteria in wild animals has become an important surveillance tool, as it could reflect antimicrobial resistance in strains isolated from humans [16].

In recent years, increasing attention has been paid to multidrug-resistant Enterobacterales, particularly ESBL-producing, plasmid-mediated AmpC β-lactamase-producing and carbapenemase-producing strains, across clinical, community, animal and environmental settings [17,18,19,20]. Within this group, ESBL-producing E. coli has been proposed as a relevant and practical indicator for AMR surveillance [21].

The aim of this narrative review is to analyze the information on the incidence, characteristics and transmission dynamics of ESBL-producing E. coli between livestock and wildlife. The public health relevance of this interface and strategies for mitigation and control are also discussed. We highlight the need to address this issue from a One Health perspective.

2. ESBL-Producing E. coli

Escherichia coli is the bacterial species most frequently described in antibiotic resistance studies in wildlife [13]. Most animal species, as well as humans, carry E. coli in their intestinal tract. Most E. coli strains are commensals that inhabit the intestinal tract of humans and animals. However, E. coli also remains one of the most frequent causes of several common bacterial infections in humans and animals. In humans, it is an important opportunistic pathogen associated with severe sepsis and urinary tract infections, among other hospital-acquired infections [22].

In animals, E. coli can also cause various infections, with respiratory infections being particularly relevant in birds [22]. Vidal et al. [23] observed that E. coli was the most common microorganism recovered from necropsies of raptors with clinical signs of septicemia or respiratory disorders, finding MDR in 71% of E. coli isolates.

In livestock, infections caused by pathogenic strains of E. coli cause significant economic losses, affect animal welfare, and have repercussions for public health due to the transmission of certain serotypes to humans. In livestock, diseases associated with pathogenic E. coli include diarrhea in piglets, calves and lambs, urinary tract infections and mastitis [24,25,26,27].

β-Lactamases are bacterial enzymes capable of hydrolyzing the β-lactam ring of β-lactam antibiotics to render these compounds inactive [28]. To facilitate understanding of their structural, functional, and clinical relevance, β-lactamases are classified using two main schemes: the Ambler molecular classification [29,30] and the Bush–Jacoby–Medeiros (BJM) functional classification [31]. The latter system is particularly valuable in clinical microbiology, as it aids in predicting antimicrobial susceptibility and guiding therapeutic decisions.

The most epidemiologically significant enzymes in this context are extended-spectrum β-lactamases (ESBLs), which have become widely disseminated worldwide. These enzymes can hydrolyze penicillins, extended-spectrum cephalosporins and aztreonam. They are included in Group 2 in the BJM classification. Although ESBLs share common biochemical properties with regard to the hydrolysis of broad-spectrum beta-lactam antibiotics and inhibition by clavulanate, the genes encoding these enzymes are diverse in nature and can be grouped into several families. Table 1 summarizes the ESBL families described in E. coli.

The genetic flexibility and adaptability of E. coli to constantly changing environments allow it to acquire a large number of antimicrobial resistance mechanisms. CTX-M type beta-lactamases are the most frequently isolated ESBLs in Enterobacteriaceae species from human and animal samples [22,32,33].

There are several reasons for using ESBL-producing E. coli as a relevant and simple indicator for AMR surveillance. Among these, it is worth highlighting the possible connection between antibiotic use in farm animals and clinical cases in humans, and the correlation between interventions focused on decreasing the exposure to antibiotics in humans and animals and the decrease in occurrence of ESBL-producing E. coli [21]. In addition to this, ESBL-producing bacteria are resistant to critically important antimicrobials including most beta-lactams so treatment with last-line antimicrobials may be required.

Table 1. ESBL families described in E. coli.

ESBL Family	Nomenclature / Origin	Main characteristics in Escherichia coli	Reference
TEM	Derived from TEM-1 and TEM-2 β-lactamases (“Temoniera”). Common variants include TEM-3, TEM-10, TEM-52.	Class A ESBLs generated by point mutations. Hydrolyze penicillins and third-generation cephalosporins. Usually inhibited by clavulanic acid. Historically among the first ESBLs detected in E. coli.	[34]
SHV	“Sulfhydryl Variable”. Common variants: SHV-2, SHV-5, SHV-12.	Class A ESBLs with mutations expanding activity toward cefotaxime and ceftazidime. Frequently plasmid-mediated and widely disseminated among Enterobacterales.	[35]
CTX-M	“Cefotaximase-Munich”. Includes CTX-M-1, CTX-M-2, CTX-M-8, CTX-M-9, and CTX-M-25 groups.	Currently the predominant ESBL family worldwide in E. coli. Strong hydrolytic activity against cefotaxime. Associated with conjugative plasmids and community/hospital dissemination. Derived from chromosomal genes of Kluyvera spp.	[34,36]
OXA	“Oxacillinases”. Includes OXA-1, OXA-10, OXA-48 variants.	Class D β-lactamases. Some variants exhibit ESBL phenotype. Hydrolyze oxacillin and some cephalosporins. Less susceptible to inhibition by clavulanic acid.	[34,37]
PER	“Pseudomonas Extended Resistance”. Example: PER-2.	Less common ESBLs in E. coli. Hydrolyze broad-spectrum cephalosporins. More frequently identified in Pseudomonas aeruginosa and Acinetobacter spp.	[34,38]
VEB	“Vietnam Extended-spectrum β-lactamase”. Example: VEB-1.	Plasmid-mediated ESBLs able to hydrolyze third-generation cephalosporins and aztreonam. Occasionally reported in E. coli.	[34,39]
GES	“Guiana Extended Spectrum”. Examples: GES-1, GES-5.	Some variants behave as ESBLs, while others evolved into carbapenemases. Frequently associated with mobile genetic elements and multidrug resistance.	[34,40]
BES	“Brazilian Extended Spectrum”.	Rare ESBL family described in Enterobacterales. Confers resistance to broad-spectrum cephalosporins.	[34]
TLA	“Tlahuicas”. Example: TLA-1.	Rare ESBL initially described in Latin America. Associated with transferable plasmids in Enterobacterales.	[34,39]
SFO	Derived from Serratia fonticola. Example: SFO-1.	Plasmid-mediated class A cefotaximase. Hydrolyzes broad-spectrum cephalosporins and often coexists with other resistance genes.	[34,41]
CMT	Complex mutant derived from TEM-1	TEM variants that are resistant to inhibition by clavulanate and sulbactam and also exhibit an ESBL phenotype.	[42]
BEL	Belgium extended β-lactamase. BEL-1 in E. coli	Preferentially hydrolyzes ceftazidime and aztreonam compared with cefotaxime.	[43]

Table 1. ESBL families described in E. coli.

ESBL Family	Nomenclature / Origin	Main characteristics in Escherichia coli	Reference
TEM	Derived from TEM-1 and TEM-2 β-lactamases (“Temoniera”). Common variants include TEM-3, TEM-10, TEM-52.	Class A ESBLs generated by point mutations. Hydrolyze penicillins and third-generation cephalosporins. Usually inhibited by clavulanic acid. Historically among the first ESBLs detected in E. coli.	[34]
SHV	“Sulfhydryl Variable”. Common variants: SHV-2, SHV-5, SHV-12.	Class A ESBLs with mutations expanding activity toward cefotaxime and ceftazidime. Frequently plasmid-mediated and widely disseminated among Enterobacterales.	[35]
CTX-M	“Cefotaximase-Munich”. Includes CTX-M-1, CTX-M-2, CTX-M-8, CTX-M-9, and CTX-M-25 groups.	Currently the predominant ESBL family worldwide in E. coli. Strong hydrolytic activity against cefotaxime. Associated with conjugative plasmids and community/hospital dissemination. Derived from chromosomal genes of Kluyvera spp.	[34,36]
OXA	“Oxacillinases”. Includes OXA-1, OXA-10, OXA-48 variants.	Class D β-lactamases. Some variants exhibit ESBL phenotype. Hydrolyze oxacillin and some cephalosporins. Less susceptible to inhibition by clavulanic acid.	[34,37]
PER	“Pseudomonas Extended Resistance”. Example: PER-2.	Less common ESBLs in E. coli. Hydrolyze broad-spectrum cephalosporins. More frequently identified in Pseudomonas aeruginosa and Acinetobacter spp.	[34,38]
VEB	“Vietnam Extended-spectrum β-lactamase”. Example: VEB-1.	Plasmid-mediated ESBLs able to hydrolyze third-generation cephalosporins and aztreonam. Occasionally reported in E. coli.	[34,39]
GES	“Guiana Extended Spectrum”. Examples: GES-1, GES-5.	Some variants behave as ESBLs, while others evolved into carbapenemases. Frequently associated with mobile genetic elements and multidrug resistance.	[34,40]
BES	“Brazilian Extended Spectrum”.	Rare ESBL family described in Enterobacterales. Confers resistance to broad-spectrum cephalosporins.	[34]
TLA	“Tlahuicas”. Example: TLA-1.	Rare ESBL initially described in Latin America. Associated with transferable plasmids in Enterobacterales.	[34,39]
SFO	Derived from Serratia fonticola. Example: SFO-1.	Plasmid-mediated class A cefotaximase. Hydrolyzes broad-spectrum cephalosporins and often coexists with other resistance genes.	[34,41]
CMT	Complex mutant derived from TEM-1	TEM variants that are resistant to inhibition by clavulanate and sulbactam and also exhibit an ESBL phenotype.	[42]
BEL	Belgium extended β-lactamase. BEL-1 in E. coli	Preferentially hydrolyzes ceftazidime and aztreonam compared with cefotaxime.	[43]

3. ESBL-Producing E. coli in Wildlife

Antibiotic resistance can be a good indicator of human influence on wildlife exposure to bacteria. Animals in the wild can acquire these bacteria from treated water, farms, landfills, and other anthropogenically impacted environments [44,45,46,47,48,49].

ESBL-producing E. coli isolates have been reported in wildlife, particularly in wild birds [33,50,51,52,53,54,55,56,57,58,59].

The carcasses of domestic animals available in the field are essential as food for scavenging birds. However, they are also their main source of exposure to veterinary drugs, which could compromise their survival. The presence of antibiotics in carcasses of domestic animals that can be ingested by necrophagous birds can contribute to selecting antibiotic-resistant bacteria in their digestive tract [58,60,61,62].

These bacteria have also been described in other groups of wild animals. Among wild mammals, ESBL-producing E. coli isolates have been described in large carnivores, such as captive lion and tiger [63] and in mesocarnivores, such as the Iberian wolf [64,65], Iberian lynx [65,66], coyotes [67], raccoons [68,69] or foxes [11,70,71].

Wild ungulates and other ruminants, such as red deer, roe deer and buffalo, have been described as carriers of ESBL-producing E. coli [72,73,74,75,76,77,78,79]. They are frequently raised on farms or share pastures with domestic ruminants, which facilitates the transmission of microorganisms. These bacteria have been described also in isolates from captive camels (Camelus dromedarius) in Canary Islands [80].

Wild boar (Sus scrofa) is considered the model animal species to study antimicrobial resistance at the WLI in Europe [81], probably due to its high population and the possible implications of contact with domestic pigs [65,76,79,82,83,84,85,86,87].

ESBL-producing E. coli have been found also in non-human primates like baboons, chimpanzees, green monkeys and gorillas [88,89,90].

Rodents have also been investigated as carriers of ESBL-producing E. coli and as potential reservoirs for livestock [91,92,93,94,95,96,97]. Prevalences found ranged from 1.5% to 5% and the rodent species most frequently cited was Rattus norvegicus.

Other small mammals, such as hedgehogs [53], coatis [98] and badgers [71] have also been described as reservoirs.

The presence of ESBL-producing E. coli in fecal samples of bats [65,99,100,101,102] is especially relevant due to the longevity of these animals, their ecological adaptability and ability for long distance flight. In addition to this, “guano” (bats’ fecal material) is commonly used in agriculture as biofertilizer, raising public health concerns.

Regarding semi-aquatic or aquatic species, ESBL-producing E. coli have been described in wild fish from the Atlantic Ocean [103] and the Mediterranean Sea [104]. Also, these bacteria have been found in minks, otters and turtles [105,106,107]. An isolate of CTX-M-15 producing E. coli was obtained from a captive dolphin in Portugal [108].

4. ESBL-Producing E. coli in Livestock

In this review, the term “livestock” is mainly used to refer to domesticated farm animals, although poultry may be considered separately in some epidemiological and production contexts. In most countries, this category usually includes cattle, sheep, goats, pigs, horses and donkeys. In some countries, animal species like llama, alpaca, camel, buffalo, reindeer or yak for example, could be included in this description.

Given their public health implications, the presence of ESBL-producing bacteria in farm animals has been analyzed in several studies. In a recent review, prevalence of ESBL-producing E. coli in healthy food-producing animals in different countries was compared. With some exceptions (UK and The Netherlands), they found that prevalence was higher in pigs than in cattle. Some countries, like Thailand (37%), China (44%), Portugal (49%), Germany (62%) and, especially, Lebanon (98%) presented very high prevalences in pigs [22].

Other later studies show similar results. Song et al. [109] found marked differences in the prevalence of ESBL-producing E. coli between pigs (69.5%) and cattle (7%) in South Korea. Similarly, Miltgen et al. [110] describe a prevalence of 18.6% in swine but 1.6% in cattle in livestock from Reunion Island. Balázs et al. [111] also found a high prevalence (72%) in pigs in Hungary. However, in Guadeloupe island, Gruel et al. [112] found a higher prevalence (14.7%) in beef cattle than in pigs (7.3%), and Chai et al. [113] did not find any among swine isolates in Malaysia. In a study done in Italy, similar prevalences (29.4% and 27%) were found for cattle and pigs [114].

Studies in other livestock species are less frequent. Among sheep, pandemic blaCTX-M-8-Producing ST224 E. coli has been described in Brazil [115]. Benavides et al. [91] found a prevalence of 7.5% in sheep from small-scale farms in Chile. They studied also goats (n=6) and horses (n=60), but no ESBL-producing E. coli was detected. High differences between ESBL-producing E. coli prevalences in healthy cattle (17%) and sheep (1%) were found in Algeria [116]. In Portugal 5.5% of sheep was found to be ESBL-producing E. coli carriers [117]. In both sheep and goats from different farms in Tanzania, prevalences of 2.3% were found [118]. In Iran, goats harboring ESBL-producing E. coli isolates have also been described [119].

In samples from diarrheic lambs (n=21), Shi et al. [120] obtained 28 E. coli isolates, of which 53.6% were ESBL producers.

About 21% of carriers were observed among farm horses in Israel [121]. In Turkey, ESBL-producing E. coli isolates were found with high frequency (53.5%) in samples from racehorses [122].

5. The Wildlife–Livestock Interface

The wildlife–livestock interface has been defined as “the physical spaces where wildlife and livestock species overlap in range and may interact, creating opportunities for direct or indirect contact that could result in pathogen transmission in either direction” [123]. Although this definition refers specifically to pathogen transmission, it is also applicable to the exchange of multidrug-resistant bacteria and antimicrobial resistance determinants. As previously highlighted, there is a marked imbalance between the large amount of data available on the prevalence of ESBL-producing E. coli in wildlife and livestock and the limited evidence regarding the actual transmission of these bacteria at the wildlife–livestock interface [7,67].

Several factors should be considered when assessing the risk of exchange of multidrug-resistant bacteria at this interface. These include the livestock species involved, the farming system, the wildlife species present in the geographic area, the type and frequency of contact between hosts, possible transmission routes, and the degree of human influence on the environment [124,125]. The definition of “wildlife” is also relevant, since different interpretations may modify the risk factors considered. According to the proposal by Jori et al. [126], wildlife would not include species that depend on humans for food or reproduction, such as feral animals, animals kept in zoological gardens or rehabilitation centers, or individuals dependent on supplementary feeding stations. Nevertheless, many studies on antimicrobial resistance in wildlife include precisely these situations, particularly when assessing the effects of anthropogenic pressure on resistant bacteria circulation [11,63,67,127].

Antimicrobial resistance in wildlife can be considered an indicator of human influence on ecosystems. Wild animals may acquire resistant bacteria from treated wastewater, farms, landfills, contaminated water bodies, agricultural environments or other anthropogenically impacted habitats [44,45,46,47,48,49]. Most publications on wild birds have focused on migratory, waterfowl or other highly mobile species [35,46,49,69]; however, urban-associated birds have also been investigated because of their public health relevance and their frequent exposure to anthropogenic sources of antimicrobial resistance [12,38,39,150].

Transmission of multidrug-resistant bacteria between wildlife and livestock may occur through several routes. Indirect transmission, through shared water sources, feed, pasture, soil, manure, fomites or contaminated environments, is generally considered the most common pathway [25,58,128]. Direct interactions between wildlife and livestock may also occur in some systems, although they are usually less frequent and more dependent on local ecological and management conditions [129,130]. In scavenging birds, carcasses of domestic animals available in the field constitute an important food resource, but they may also represent a source of exposure to veterinary drugs. The presence of antimicrobial residues in livestock carcasses consumed by necrophagous birds may contribute to the selection of resistant bacteria in their digestive tract, with possible implications for wildlife conservation and environmental dissemination of resistance [58,60,61,62].

Most available information on multidrug-resistant bacteria in wildlife is still based on prevalence studies. However, the detection of resistant bacteria in wild animals does not necessarily demonstrate their ability to transmit these microorganisms to livestock, humans or other wildlife species. Important knowledge gaps remain regarding whether these bacteria survive long enough in wild hosts or in the environment, and whether they are present at sufficient infectious doses to cause colonization or infection in other hosts. Future research should therefore assess the capacity of wildlife to disseminate resistant bacteria of relevance to livestock or public health, while also identifying where and how wild animals acquire these bacteria. This is essential both for limiting the spread of antimicrobial resistance and for reducing potential adverse effects on threatened wildlife populations [131].

Several studies have investigated the potential exchange of resistant E. coli and resistance determinants at the wildlife–livestock interface, although direct evidence of transmission remains scarce. Liu et al. [67] studied the genetic relatedness of ESBL-producing E. coli in wildlife and cattle sharing habitat using shotgun metagenomic sequencing. Although ESBL-producing bacteria were detected in feral swine, no direct evidence of transfer to grazing cattle was found. However, bacteria carrying other resistance genes, including genes conferring resistance to tetracyclines and macrolides, were present in both animal groups, suggesting that feral swine could theoretically contribute to the exchange of resistant bacteria or resistance determinants with cattle.

In South Africa, Van den Honert et al. [132] compared antimicrobial resistance patterns of E. coli isolates from co-grazing and non-co-grazing livestock and wildlife species. Their results suggested that antimicrobial-resistant E. coli and resistance genes may be exchanged between livestock and wildlife sharing grazing areas, although clear evidence of ESBL transmission was not demonstrated. Similarly, Kozak et al. [133] showed that wild small mammals trapped on farms were five times more likely to carry tetracycline-resistant E. coli than animals trapped in natural areas, supporting the influence of livestock-associated environments on wildlife exposure to resistant bacteria.

At the buffalo–cattle interface in Southern Africa, Mercat et al. [134] found differences in antimicrobial resistance among E. coli isolates from buffalo populations with and without contact with cattle. No resistant E. coli strains were isolated from buffalo without cattle contact, whereas resistance was detected in buffalo sharing areas with cattle. A narrow-spectrum beta-lactamase-producing E. coli isolate carrying TEM-1 was found in both cattle and the in-contact buffalo population. In contrast, Navarro-González et al. [135] found no correlation between antimicrobial resistance in E. coli isolated from free-ranging cattle and cohabiting wild ungulates, including Iberian ibex and wild boar, in a natural environment.

Other studies have highlighted the role of anthropogenic pressure in shaping bacterial exchange among humans, livestock and wildlife. In Uganda, Rwego et al. [136] analyzed E. coli transmission among mountain gorillas, livestock and humans. Gorillas living in anthropogenically influenced areas harbored E. coli strains genetically similar to those from livestock and humans, whereas isolates from gorillas that did not share habitat with humans or livestock were genetically distinct. Although ESBL production was not investigated, this study illustrates how human and livestock proximity may influence bacterial exchange in wildlife populations.

More recent genomic approaches have provided stronger evidence for local circulation of ESBL-producing E. coli among domestic and wild animals. Using whole-genome sequencing, Hayer et al. [137] studied ESBL-producing E. coli transmission dynamics in livestock, dogs and wild rodents in Chile. Nearly identical clones, carrying similar antimicrobial resistance genes, heavy metal resistance genes and virulence-associated genes, were detected in dogs, cattle and sheep from the same farm, as well as in a dog and a wild rodent from a nearby farm located approximately 15 km away. These findings support the possibility that resistant clones and plasmids may circulate among livestock, companion animals and wildlife in agricultural landscapes.

Overall, current evidence indicates that the wildlife–livestock interface can contribute to the circulation of multidrug-resistant bacteria and resistance determinants, but the magnitude and direction of transmission remain difficult to establish. Wildlife may act as a reservoir, spillover host, sentinel or disperser of antimicrobial resistance depending on the species, habitat, degree of human influence and type of contact with livestock. However, the mere detection of resistant bacteria in wildlife should not be interpreted as proof of effective transmission to livestock or humans. Future studies should move beyond prevalence data and combine simultaneous sampling of livestock, wildlife and environmental matrices with genomic analysis, ecological information and epidemiological modeling. Such integrated One Health approaches are needed to determine whether resistance dissemination at the wildlife–livestock interface occurs through clonal transmission, plasmid exchange, shared environmental contamination or broader anthropogenic pressure.

6. Public Health Implications

Although this review focuses on ESBL-producing E. coli, selected examples involving other antimicrobial-resistant bacteria are mentioned when they illustrate shared transmission routes, biosecurity challenges or One Health mechanisms relevant to the wildlife–livestock interface.

6.1. Risks of Transmission to Humans Through Direct Contact or Food

The public health relevance of antimicrobial-resistant bacteria at the wildlife–livestock–human interface lies in their capacity to circulate among food-producing animals, humans and the environment [138]. Food-producing animals may contribute to the emergence, maintenance and dissemination of resistant bacteria, which can subsequently reach humans through contaminated food products, direct animal contact or environmental exposure [138]. In the case of ESBL-producing Escherichia coli, livestock and food products represent relevant sources of concern, as human exposure may occur through contact with colonized animals or through the consumption or handling of contaminated food [139]. Similarly, human colonization or infection with multidrug-resistant bacteria may occur through foods of animal origin, including meat, milk and eggs, as well as through direct contact with animals [140].

Occupationally exposed populations, such as farmers, farm workers and slaughterhouse personnel, are particularly relevant because resistant bacteria may circulate between animals, farm environments and humans. Although most evidence at this interface concerns ESBL-producing Enterobacterales, studies in pig production have also shown that livestock-associated resistant bacteria can be detected in animals, barn air, abattoir environments and farm workers. Schmithausen et al. reported livestock-associated methicillin-resistant Staphylococcus aureus (MRSA) in pigs, barn air and humans, while evidence for ESBL-producing Enterobacterales transmission from pigs to humans was less conclusive. These findings illustrate that farm and slaughterhouse environments may act as relevant interfaces for the dissemination of antimicrobial-resistant bacteria, including ESBL-producing E. coli [141].

Foodborne exposure is a major route by which resistant bacteria from animals may reach humans [140]. Although ESBL-producing E. coli is the focus of this review, other foodborne pathogens illustrate the public health relevance of this pathway. For example, multidrug-resistant ESBL-producing Salmonella enterica serovar Infantis has been epidemiologically linked to contaminated chicken meat and human infections, supporting the need for control measures at both livestock and food-chain levels [142].

The public health significance of ESBL-producing E. coli is further increased when these isolates also harbor resistance determinants against critically important antimicrobials, such as fluoroquinolones or colistin. The detection of mobile colistin resistance genes, including mcr, in bacteria from food-producing animals is particularly concerning because these determinants may be transferred between commensal E. coli and other foodborne bacteria [139,143].

Wildlife may contribute indirectly to human exposure by acting as a reservoir, sentinel or disperser of resistant bacteria across natural, livestock-associated and human-associated environments. Plaza-Rodríguez et al. [79] detected ESBL-/AmpC-producing E. coli in wild boars, roe deer, wild ducks and geese, although the overall prevalence of resistant bacteria in the selected wildlife species in Germany was low. Importantly, the authors cautioned that the carriage of resistant bacteria by wildlife does not necessarily demonstrate that wild animals are effective vehicles of transmission to humans or livestock. Nevertheless, wild birds may act as long-distance disseminators of resistant bacteria because of their migratory behavior and broad spatial range.

Brendecke et al. [144] identified ESBL-producing E. coli and Klebsiella pneumoniae in black-headed gulls, including high-risk E. coli lineages such as ST131, ST38 and ST58. The detection of strains combining antimicrobial resistance and virulence-associated genes in wildlife supports the inclusion of wild animal populations in One Health surveillance frameworks.

At the same time, transmission should not be interpreted as universally direct or unidirectional. Genomic One Health studies may identify shared resistance determinants or mobile genetic elements without demonstrating direct animal-to-human strain transmission. Nguyen et al. [145] reported distinct blaCTX-M-harboring E. coli strains and plasmids in food animals and humans with community-acquired urinary tract infections, suggesting the existence of evolutionary barriers to direct strain or plasmid transfer across host species. However, the same study identified common insertion sequence elements flanking blaCTX-M variants across different sample sources, supporting the potential dissemination of resistance genes within or between habitats.

Overall, current evidence indicates that humans may be exposed to antimicrobial-resistant and zoonotic bacteria through direct animal contact, animal-associated environments and contaminated foods. However, the relative contribution of each pathway depends on the bacterial species involved, the production system, hygiene and biosecurity standards, food-chain controls and local environmental conditions [139,145,146].

6.2. Public Health Implications and One Health Relevance of Antimicrobial Resistance

Antimicrobial resistance at the wildlife–livestock–human interface represents a major public health concern because resistant bacteria and mobile resistance determinants can circulate among humans, animals, food products and the environment [146]. This problem is no longer confined to healthcare settings, as ESBL-producing Enterobacteriaceae have increasingly been reported in the community, including in healthy humans, food-producing animals, companion animals, wildlife and environmental reservoirs [144,147,148].

Food-producing animals constitute important reservoirs of antimicrobial resistance, since ESBL-producing and multidrug-resistant E. coli have been repeatedly detected in cattle, pigs, poultry and their associated production environments [149]. The public health significance of these reservoirs is reinforced by the possibility that resistant bacteria may reach humans through direct contact with animals, contaminated food products or environmental pathways [150].

Foodborne exposure is particularly relevant because ESBL/AmpC-producing E. coli and Klebsiella pneumoniae can contaminate food products during production, slaughter and processing. The detection of ESBL/AmpC-producing bacteria in meat and vegetables, especially in broiler meat subsamples, supports the need to consider the food chain as an important route of human exposure [151].

Direct contact with animals and their environments also represents a relevant transmission pathway. ESBL-producing E. coli have been identified in livestock workers, and similar resistance genes or sequence types have been reported in humans and animals from farm settings [149]. Nevertheless, direct animal-to-human transmission should not be assumed in all cases. Some genomic One Health studies have identified distinct human and animal lineages despite the presence of shared resistance determinants, indicating that transmission dynamics may be complex and shaped by ecological, bacterial and host-related barriers [145].

Wildlife may contribute to the environmental ecology of antimicrobial resistance by acting as reservoirs, sentinels or dispersers of resistant bacteria across natural and human-associated ecosystems [79,149]. The detection of ESBL-producing E. coli and high-risk K. pneumoniae lineages in wild birds further supports the inclusion of wildlife in integrated antimicrobial resistance surveillance systems [144].

A One Health approach is therefore essential, because antimicrobial resistance emerges and disseminates through interconnected human, animal, food-production and environmental reservoirs. At the local scale, One Health surveillance enables the comparative analysis of resistant bacteria, resistance genes and mobile genetic elements from humans, animals, food products and environmental samples, thereby helping to identify possible transmission routes and shared sources [146,152]. At the global scale, this approach is equally important, as international travel, food trade and the movement of animals and goods may facilitate the transboundary dissemination of resistant bacteria, plasmids and resistance genes [151].

Mobile genetic elements play a central role in this process. Plasmids, integrons, transposons and insertion sequences can mobilize resistance genes, such as blaCTX-M, across bacterial populations, host species and ecological compartments [148]. Consequently, surveillance should not be limited to bacterial species alone, but should also include resistance genes, plasmid lineages and other mobile genetic elements that may link animal, human and environmental reservoirs [139,151].

Overall, the available evidence supports integrated surveillance across livestock, wildlife, companion animals, food products, humans and environmental matrices as a core public health strategy [148]. Mitigation efforts should combine prudent antimicrobial use, improved hygiene and biosecurity, better sanitation, safe food-handling practices, environmental control and genomic surveillance within a coordinated One Health framework [139,151].

6.3. Potential of Wildlife as a Source of Reintroduction of Resistance into Controlled Environments

Wildlife may act as a potential source of reintroduction of antimicrobial-resistant bacteria into controlled or partially controlled environments, particularly when livestock, companion animals, wild animals and environmental matrices share water sources, soil, pasture, feed, manure or peri-farm spaces. This risk is especially relevant because, although wild animals are not usually exposed to antimicrobial treatment, they can acquire antimicrobial-resistant bacteria from contaminated environments and subsequently transfer them to livestock or other animals through direct or indirect contact [149].

External biosecurity in animal production is intended to prevent the introduction of pathogens from the surrounding environment through vectors such as humans, vehicles, companion animals, wild animals, rodents, water and feed [153]. Therefore, even in farms or facilities where antimicrobial use, cleaning and disinfection are strictly controlled, wildlife and environmental reservoirs may compromise biosecurity by reintroducing resistant bacteria or resistance genes from outside the managed system. The farm environment itself provides multiple interfaces for this process, as ESBL-producing E. coli have been reported in manure-amended soil, barn dust, feed mixers, animal feed, bedding material and water troughs. Wild birds are particularly relevant in this context because their mobility enables them to acquire resistant bacteria in anthropogenically impacted areas and disseminate them to farms, natural habitats or remote environments [149].

Fuentes-Castillo et al. provided genomic evidence that migratory and resident gulls in Patagonia can carry multidrug-resistant E. coli producing CTX-M-type ESBLs. In that study, gull isolates belonged to international E. coli sequence types ST295 and ST388 and carried clinically relevant blaCTX-M genes. Phylogenomic analysis clustered these gull isolates with E. coli strains from environmental, companion animal and livestock sources in the United States, suggesting the possible transhemispheric movement of international ESBL-producing clones along migratory routes [56].

Similarly, Brendecke et al. detected ESBL-producing E. coli and Klebsiella pneumoniae in black-headed gulls from German conservation islands, including strains phylogenetically related to isolates from humans, livestock, food and environmental sources. These findings support the concept that wild birds may connect anthropogenic and natural ecosystems and contribute to the long-distance dissemination of multidrug-resistant bacteria [144].

Hayer et al. provided direct local evidence that ESBL-producing E. coli can circulate among domestic and wild animals in agricultural settings. In their study in Chile, nearly identical ESBL-producing E. coli clones were identified in dogs, cattle or sheep from the same farm, as well as in a dog and a wild rodent living in close proximity. These findings support the possibility that wildlife and peri-domestic animals may participate in the maintenance and re-entry of resistant clones into farms after control measures have been implemented. The same study showed that dissemination across animal species may occur through both clonal transmission and plasmid spread, which is particularly relevant because plasmids can maintain and disseminate resistance genes even when bacterial lineages differ. The presence of clinically relevant lineages, such as ST410, ST58, ST88 and ST617, in animals without apparent signs of disease further indicates that resistant clones with pathogenic potential may circulate silently in animal populations [137].

Wildlife should therefore be considered in surveillance and control programs not only as a passive indicator of environmental contamination, but also as a potential ecological bridge for the reintroduction of resistance into livestock, companion animal or managed wildlife settings [154]. Nevertheless, the role of wildlife should not be overgeneralized, as the detection of resistant bacteria in wild animals does not, by itself, demonstrate efficient transmission to livestock or humans [79]. For this reason, integrated One Health surveillance should combine wildlife sampling, livestock monitoring, environmental sampling and genomic analysis to determine whether reintroduction occurs through the movement of bacterial clones, plasmids or shared resistance genes [137].

From a control perspective, these findings support the reinforcement of perimeter biosecurity, restriction of wildlife access to feed and water, improved manure and waste management, systematic monitoring of rodents and wild birds, and the incorporation of wildlife into antimicrobial resistance surveillance programs [149].

7. Strategies for Mitigation and Control

7.1. Reduction of Antimicrobial Use in Livestock

Reducing antimicrobial use in livestock is a central component of AMR mitigation because antimicrobial use in food-producing animals is recognized as a significant contributor to the development and spread of resistant bacteria and resistance genes. The intensive use of antibiotics in food-producing animals can select resistant bacteria that may subsequently reach humans through food products, direct animal contact or environmental pathways. Antimicrobial use in livestock is not limited to therapeutic treatment, as antimicrobials may also be used for metaphylaxis, prophylaxis and growth promotion [138].

Inappropriate and excessive antimicrobial use is a recognized driver of AMR, and the use of antimicrobials for prophylaxis or growth promotion may also compensate for poor hygiene or suboptimal management conditions [154]. Therefore, reduction strategies should prioritize the elimination of unnecessary antimicrobial use while preserving appropriate therapeutic treatment when animal health and welfare require it [155]. The restriction of medically important antimicrobials for growth promotion is consistent with international recommendations aimed at reducing selection pressure in food-producing animals [154].

Within a One Health framework, reducing unnecessary antibiotic use in food-producing animals and restricting medically important antimicrobials are key measures to limit AMR dissemination across animal, human and environmental reservoirs [138]. Evidence reviewed by Olaru et al. indicates that interventions restricting antimicrobial use in animals can reduce the burden of AMR in animals and are likely to reduce AMR in humans [154]. However, reduction should not be interpreted only as a quantitative decrease in antimicrobial consumption, because antimicrobial stewardship also requires appropriate selection, dosage and duration of treatment. Antimicrobial stewardship in livestock should therefore promote evidence-based treatment, avoidance of unnecessary group medication, and limitation of prophylactic or growth-promoting uses [149].

The implementation of antibiotic-free or organic production systems may contribute to lower resistance to some antimicrobials, as Musa et al. observed lower levels of cefotaxime-, ceftazidime- and ciprofloxacin-resistant E. coli in organic broiler systems compared with conventional systems. Nevertheless, the same study found higher prevalence of tigecycline-, azithromycin- and gentamicin-resistant E. coli in organic samples, suggesting that reducing on-farm antimicrobial use does not fully prevent the occurrence of resistant bacteria. This finding supports the view that antimicrobial reduction must be accompanied by environmental control and production-chain monitoring, because external contamination may contribute to resistant strains even in systems with limited antimicrobial use [155].

Preventive strategies that reduce disease pressure are also needed, since poor biosecurity, low vaccination coverage and inadequate nutrition can favor disease outbreaks and increase reliance on preventive antibiotic use [140].

Subramanya et al. recommend immunization, public awareness and education, improved hygiene standards, antibiotic stewardship, genomic surveillance, reduced antibiotic use in agriculture and livestock, and good husbandry practices as part of AMR mitigation [148].

Alternative approaches such as prebiotics, probiotics, phage therapy, vaccines, antimicrobial peptides and antimicrobial polymers may help reduce dependence on antibiotics, although their effectiveness has not yet been fully evaluated. Consequently, these alternatives should be incorporated cautiously as part of broader prevention programs rather than presented as universally validated replacements for antibiotics [149].

Reliable antimicrobial-use data are also essential, because current estimates of antimicrobial consumption in animals remain uncertain and are affected by limited standardization across studies and countries. For this reason, antimicrobial reduction policies should include farm-level recording systems, monitoring of veterinary prescriptions and integration of antimicrobial-use data with AMR surveillance [154].

At the environmental level, reducing antibiotic use in animals is also relevant because antimicrobial residues and resistant bacteria can enter soil and water through animal waste and food-production systems. Martak et al. identify reducing antibiotic use in humans and animals, regulating antibiotic distribution, and prioritizing less environmentally persistent antibiotics as key levers to reduce AMR in environmental reservoirs [146].

Overall, reduction of antimicrobial use in livestock should be framed as an integrated One Health intervention combining prudent use, restriction of non-essential indications, disease prevention, improved husbandry, vaccination, environmental management and continuous surveillance [148].

7.2. Biosecurity Measures on Farms

Farm biosecurity is a key component of AMR mitigation because it reduces the introduction, persistence and spread of infectious agents within and between animal populations, thereby decreasing the need for therapeutic or prophylactic antimicrobial use. At farm level, infection control through biosecurity and disease-control programs is particularly relevant in intensive food-animal industries, especially poultry and swine production. However, the direct effectiveness of these programs in limiting antimicrobial resistance, particularly in non-pathogenic bacteria, is rarely evaluated, and this limitation should be acknowledged when interpreting biosecurity as an AMR-control measure [152].

Biosecurity measures should therefore be framed not as a stand-alone intervention, but as part of an integrated prevention strategy combining herd health, hygiene, environmental management, prudent antimicrobial use and surveillance. Established veterinary approaches to reduce infectious disease include improved husbandry, quarantine, biosecurity measures, vaccination, vector control, antiseptic practices and competitive-exclusion strategies. These interventions are relevant to AMR control because prevention of viral and bacterial disease can reduce secondary bacterial infections and decrease the need for antimicrobial therapy [152].

External biosecurity should aim to prevent the entry of resistant bacteria into farms through animals, people, vehicles, feed, water, wildlife, rodents, birds, insects and contaminated environmental matrices [156].

Internal biosecurity should limit the dissemination of resistant bacteria between groups of animals, pens, houses and production stages within the same farm. All-in, all-out management can help maintain physical separation between successive animal groups and reduce the dissemination of resistant bacteria and their resident microbiota [152].

Effective cleaning and disinfection of barns, pens and production sites after depopulation are additional measures to control infectious diseases and reduce pathogen spread. Specific measures described for preventing the introduction and spread of Salmonella include restricting farm access, requiring visitors to change clothing and boots, controlling birds and rodents, using Salmonella-free feed and applying disinfectant footbaths [152].

Environmental hygiene within the farm is also essential, because ESBL-producing E. coli have been detected in manure-amended soil, barn dust, feed mixers, animal feed, bedding and water troughs. The detection of resistant bacteria in these matrices supports the inclusion of manure management, dust control, water hygiene, feed hygiene and bedding management in farm biosecurity plans. The farm environment should be considered a potential reservoir and transmission interface, since ESBL-producing bacteria and resistance genes can move through manure, soil, water, air, wildlife and farm workers. Wildlife control is relevant because wild animals may acquire resistant bacteria from contaminated environments and transfer them to livestock through shared resources such as pasture, water or soil. Wild birds, rodents and flies should be considered in biosecurity planning because they may act as carriers or mechanical vectors of ESBL-producing bacteria in livestock-associated environments. This is particularly important in open or semi-open production systems, where contact between livestock, wildlife, insects and environmental reservoirs is more difficult to prevent [149].

Water and waste management are also central to farm biosecurity, as resistant microorganisms and ARGs may enter soil, air, water and sediments through agricultural waste, manure, wastewater and other environmental hotspots. Consequently, AMR-oriented biosecurity should include safe manure storage and treatment, prevention of runoff, protection of drinking-water sources and control of wastewater contamination [157].

For MRSA and other resistant staphylococci, general hygiene, infection-control routines, environmental disinfection, isolation and treatment of infected animals, and hygienic handling of milk and meat products are recommended control measures. Food-chain hygiene, including control measures during slaughter, processing and handling, is also relevant to reduce contamination with ESBL-producing E. coli and other antimicrobial-resistant bacteria [158].

The relevance of such measures is reinforced by the fact that MRSA is no longer an exclusively hospital-associated problem, as community-associated and livestock-associated MRSA lineages are also recognized [159].

Companion animals and peri-farm animals should not be ignored, because livestock-associated MRSA lineages have been detected in pets even without direct contact with livestock [147].

Biosecurity measures should also be linked to antimicrobial stewardship, because preventing disease reduces the need for routine prophylaxis, metaphylaxis and group antimicrobial treatments [152]. Lee et al. specifically indicate that improved farm hygiene and biosecurity may decrease the prevalence and concentration of antimicrobial-resistant microorganisms in livestock. Examples of farm-management practices associated with lower detection of resistant microorganisms include frequent cleaning of drinking-water troughs, quarantine programs and appropriate disposal of dead animals [149].

Nevertheless, disinfection practices should be used carefully because antimicrobial resistance genes and quaternary ammonium compound resistance genes may be genetically linked. This means that biosecurity should rely on well-designed hygiene protocols, rather than indiscriminate or excessive use of disinfectants [152].

Overall, biosecurity in livestock farms should combine controlled animal movements, visitor and vehicle management, quarantine, all-in/all-out systems, cleaning and disinfection, pest and wildlife control, feed and water hygiene, manure management, isolation of infected animals and integrated AMR monitoring [149,152].

7.3. Importance of Integrated Surveillance Across Livestock, Wildlife and the Environment

Integrated surveillance is essential for AMR mitigation because resistant bacteria and resistance determinants circulate across livestock, wildlife, food, humans and environmental compartments. From a One Health perspective, surveillance should not be restricted to clinical settings, but should also include farms, veterinary clinics, food products and environmental matrices such as wildlife, soil and water. Such surveillance is necessary to estimate the magnitude, distribution patterns and health burden of AMR at national, regional and international levels. It is also needed to detect emerging resistance trends of clinical relevance for humans and animals, guide antimicrobial-use policies and evaluate the effectiveness of control interventions [160].

At the local level, One Health surveillance should assess the genetic relatedness of antibiotic-resistant bacteria, resistance genes and mobile genetic elements isolated from humans, animals, food products and the environment. This approach makes it possible to distinguish between potential bacterial transmission and the dissemination of resistance determinants through genetic exchange. Environmental surveillance is particularly important because the environment can act both as a reservoir of resistance genes and as a niche in which antimicrobial resistance may emerge, persist and disseminate under anthropogenic pressure [146].

In livestock systems, surveillance should identify critical control points at which resistant microorganisms are likely to be transmitted between animals and the environment. Lee et al. emphasized that transmission rates through different vehicles or sources should be quantified and incorporated into transmission models to assess risks at the interface level. Integrated AMR surveillance should therefore combine microbiological isolation, antimicrobial susceptibility testing, molecular typing, genomic analysis, ecological data and epidemiological modelling [149].

Wildlife should be included because wild animals can act as bioindicators or sentinels of resistant bacteria present in the environment. Plaza-Rodríguez et al. found that, even when the overall prevalence of resistant bacteria in selected wild animals was low, wildlife isolates reflected resistance traits to high-priority substances such as third-generation cephalosporins, fluoroquinolones and colistin. Continuous monitoring of AMR in wildlife by selective isolation is therefore advisable, particularly when resistance to critically important antimicrobials may occur at low prevalence. However, the detection of resistant bacteria in wildlife should not automatically be interpreted as evidence that wild animals are efficient vehicles of transmission to livestock or humans. Surveillance programs should therefore be designed to determine whether wildlife acts as a reservoir, sentinel, spillover host or active disperser of AMR. Standardization and harmonization of sampling strategies, laboratory methods and antimicrobial susceptibility interpretation are also required to enable meaningful comparisons of wildlife AMR data between countries [79].

Highly mobile wildlife species deserve particular attention because birds and bats may disseminate resistant bacteria over long distances [154]. Genomic surveillance of wild birds can provide evidence of long-range dissemination. For example, Fuentes-Castillo et al. identified ESBL-producing E. coli ST295 and ST388 carrying clinically relevant blaCTX-M genes in migratory and resident gulls from Patagonia. The phylogenomic clustering of these gull isolates with strains from environmental, companion animal and livestock sources supports the value of wildlife genomic surveillance for detecting international AMR dissemination routes [56].

Local simultaneous sampling is also important, because studies restricted to a single population or broad spatial comparisons may fail to detect cross-species transmission at the farm interface. Hayer et al. showed that nearly identical ESBL-producing E. coli clones were present in dogs, cattle or sheep from the same farm, as well as in a dog and a wild rodent living in close proximity. These findings support the inclusion of livestock, dogs, peri-domestic animals and wildlife in farm-level AMR surveillance. The same study also showed that AMR spread across animal species may occur through both clonal transmission and plasmid dissemination [137].

Food-chain surveillance should also be integrated, because globally traded food products can carry ESBL/AmpC-producing E. coli and Klebsiella pneumoniae harboring multidrug resistance genes and potentially epidemic plasmids. Kurittu et al. reported similarities between food-derived plasmids and plasmids previously recovered from livestock-associated and human clinical sources from different countries. These findings support the need for One Health surveillance systems that include not only livestock and wildlife, but also food products and international trade pathways [151].

Human, animal and environmental sampling should be interpreted jointly. Subramanya et al. detected ESBL-producing Enterobacteriaceae in farmers, children, livestock and environmental samples in rural Nepal. The predominance of blaCTX-M-15 in human and animal isolates in that study illustrates the value of integrated molecular surveillance in rural farming communities [148].

Genomic surveillance is particularly useful because it can clarify whether resistance dissemination reflects direct clonal transmission, plasmid exchange or the spread of shared mobile genetic elements. Nguyen et al. illustrate this point, as their One Health surveillance study in Vietnam did not support direct food-animal-to-human transmission of blaCTX-M-harboring E. coli strains or plasmids, but did identify common genetic elements across habitats. This type of evidence helps avoid overinterpretation of animal-to-human transmission while still recognizing the importance of shared resistance determinants across reservoirs [145].

Properly designed monitoring programs are required to generate reliable data, including appropriate selection of sentinel organisms, sampling strategies, culture methods and antimicrobial susceptibility testing protocols. Lack of standardization may lead to misinterpretation, underreporting or unnecessary responses, with potential consequences for both animal and public health. Overall, integrated surveillance across livestock, wildlife and the environment should be considered a core mitigation tool, as it enables the identification of reservoirs, detection of emerging resistance, clarification of transmission pathways, implementation of targeted biosecurity measures and evaluation of antimicrobial-use reduction policies [152,160].

8. Conclusions and Future Perspectives

Antimicrobial resistance at the wildlife–livestock–human interface should be understood as a dynamic and bidirectional process rather than as a linear pathway from livestock to humans [149,157]. Resistant bacteria, resistance genes and mobile genetic elements may circulate among food-producing animals, wildlife, humans, food products and environmental matrices, and interventions implemented in one sector may influence the others [146,149,152].

This bidirectionality is particularly relevant because wildlife can acquire antimicrobial-resistant bacteria from contaminated environments and may subsequently transfer them to livestock. Conversely, livestock-associated bacteria and resistance determinants may reach wildlife through shared water sources, soil, pasture, manure or peri-farm habitats [149]. Evidence of both clonal and plasmid-mediated circulation of ESBL-producing E. coli among livestock, dogs and wildlife in agricultural settings reinforces the need to consider domestic animals, peri-domestic species and wildlife as interconnected components of the same epidemiological system [137].

However, the detection of resistant bacteria or shared resistance determinants in different reservoirs should not be automatically interpreted as evidence of direct transmission. Genomic studies may identify shared mobile genetic elements without demonstrating direct animal-to-human or wildlife-to-livestock strain transfer [145]. Future studies should therefore move beyond prevalence-based approaches and integrate epidemiological, ecological and genomic data to distinguish between clonal transmission, plasmid dissemination and broader environmental circulation of resistance genes [56,145,149].

The One Health approach provides the most appropriate framework for addressing this challenge, as it explicitly connects human health, animal health, wildlife, food systems and environmental quality [155]. Interdisciplinary research involving veterinarians, microbiologists, ecologists, epidemiologists, environmental scientists, food-safety specialists and public-health authorities is needed to understand how antimicrobial resistance emerges, persists and spreads across these interconnected reservoirs [146,155]. Such an approach is essential because the drivers of antimicrobial resistance include antimicrobial use in humans and animals, infection-control practices, farming systems, waste management, sanitation, environmental contamination, wildlife ecology and food-chain dynamics [146,149,155,157].

Future monitoring programs should combine livestock sampling, wildlife surveillance, food-chain monitoring and environmental sampling of water, soil, manure, wastewater and farm-associated matrices [149,151,155]. Surveillance should not focus solely on bacterial species, but should also include antimicrobial susceptibility profiles, resistance genes, plasmids, insertion sequences, transposons and other mobile genetic elements that may link different reservoirs [145,151,155]. Whole-genome sequencing and, when feasible, long-read or hybrid sequencing approaches should be prioritized because they can clarify whether resistance dissemination is driven by bacterial clones, epidemic plasmids or shared genetic platforms [56,145,151,153].

Wildlife should be incorporated into AMR monitoring programs as a potential reservoir, sentinel or disperser of resistant bacteria, particularly in species with high mobility, close contact with livestock or frequent exposure to anthropogenic environments [79,149,153]. Selective isolation may be especially useful in wildlife surveillance when the expected prevalence of resistant bacteria is low but resistance to critically important antimicrobials, such as third-generation cephalosporins, fluoroquinolones or colistin, is of particular concern [79]. Local and simultaneous sampling of livestock, companion animals, wildlife and the farm environment should also be encouraged, as broad spatial comparisons or studies restricted to a single population may miss transmission events occurring at farm level [56].

Monitoring programs should also collect data on antimicrobial use, animal movements, farm hygiene, biosecurity practices, manure management, water sources, wildlife access and food-production practices, because these variables are necessary to identify critical control points [149,155,160]. Control programs should combine prudent antimicrobial use, reduction of unnecessary prophylactic and growth-promoting uses, improved husbandry, vaccination, farm biosecurity, hygiene, pest and wildlife control, safe manure management and protection of water sources [149,155,160].

The effectiveness of these interventions should be evaluated through continuous surveillance, because antimicrobial resistance may persist or re-enter controlled systems through environmental reservoirs, mobile genetic elements, wildlife, food products or animal movements [56,149,151,155]. Standardized sampling strategies, harmonized laboratory methods and comparable antimicrobial susceptibility interpretation criteria are essential to generate reliable data and avoid underreporting, misinterpretation or disproportionate responses [79,155,160].

In conclusion, recognizing the bidirectional and ecological nature of antimicrobial resistance is essential for designing effective mitigation strategies at the livestock–wildlife–environment interface [149,155]. Future policies should prioritize integrated One Health surveillance, genomic epidemiology, environmental risk assessment and targeted farm-level interventions to reduce the emergence, persistence and reintroduction of resistant bacteria in animal production systems [56,149,155,160].