AB toxins have historically been associated with significant morbidity, mortality through infections such as botulinum, anthrax, cholera, and diphtheria. These AB toxin-mediated diseases remain prevalent in low and middle income countries, with intermittent outbreaks of Shiga toxin-producing Escherichia coli (STEC) or whooping cough by Bordetella pertussis in high-income countries. These reports warrant an investigation to better understand the distinct characteristics of AB toxins derived from different pathogens. As toxigenic pathogens broaden their scope and diversity, it amplifies the complexity of the problems posed by their AB toxins. Here, we discuss the history, structure and characteristics of key AB toxins, and report on historical and ongoing research on these toxins. We also explore research avenues that hold great promise in potentially improving clinical management of toxin-mediated diseases in the future.

The sharing of genome sequences in online data repositories, allows for large scale analyses of specific genes or gene families. This can result in the detection of novel gene subtypes as well as development of improved detection methods. Here we used publicly available WGS data to detect a novel Stx subtype, Stx2n in two clinical E. coli strains isolated in the USA. During this process, additional Stx2 subtypes were detected; six Stx2j one Stx2m strain and one Stx2o, all were analyzed for variability from the originally described subtypes [1,2]. Complete genome sequences were assembled from short or long read sequencing and analyzed for serotype, and ST types. The stx2n and Stx2o WGS were further analyzed for virulence genes pro-phage analysis and phage insertion sites. Nucleotide and amino acid maximum parsimony trees showed expected clustering of the previously described subtypes and a clear separation of the novel Stx2n subtype. WGS data was used to design OMNI PCR primers for the detection of all known Stx1 (283 bp amplicon), Stx2 (400 bp amplicon), eae (222bp amplicon) and Stx2f (438 bp amplicon) subtypes. These primers were tested in three different laboratories, using standard reference strains. Analysis of complete genome sequence showed variability in serogroup, virulence genes, ST type, and Stx2 pro-pages showed variability in size, gene composition, and phage insertion sites. The isolates with Stx2n and Stx2o in this study demonstrated toxicity for Vero cells. The Stx2n strain were induced when grown with sub-inhibitory concentrations of Cip, and toxicity was detected. Taken together, these data highlight the need to reinforce genomic surveillance to identify the emergence of potential new Stx2 or Stx1 variants. The importance of this surveillance has a paramount impact in public health. Per our description in this study, we suggest that 2017C-4317 be designated as the Stx2n type-strain.

Inappropriate antimicrobial treatment can pose a risk for developing resistance against antimi-crobial drugs in bacteria. Close human contact might have a higher chance of being transmitted to humans from sheep if the sheep population is a potential reservoir of zoonotic pathogens such as shiga toxin-producing Escherichia coli (E. coli) (STEC). Therefore, this study aimed to exam-ine the sheep population in rural Bangladesh for antimicrobial resistant STEC. We screened 200 faecal samples collected from sheep in three Upazila from the Chattogram district. Phenotypical-ly positive E. coli isolates were examined for two shiga toxin-producing genes – stx1 and stx2. PCR positive STEC isolates were investigated for the presence of antimicrobial resistance genes- blaTEM, sul1 and sul2. In total, 123 of the 200 tested samples were confirmed positive E. coli by cul-tured based methods. PCR results show 17(13.8%) E. coli isolates harboured ≥ one virulent gene (stx1 or/and stx2) of STEC. Six of the tested STEC isolates exhibited blaTEM gene; eight STEC isolates had sul1 gene, and sul2 gene was detected in ten STEC isolates. To our knowledge, this study is the first to reveal a significant proportion of STEC isolated from sheep in rural Bangla-desh harbouring antimicrobial resistance genes.

Shiga toxin (Stx) produced by Escherichia coli is the main pathogenic factor of diarrhea-associated hemolytic uremic syndrome (HUS), which is characterized by obstruction of renal microvasculature by platelet-fibrin thrombi. It is well known that the oxidative imbalance generated by Stx induces platelet activation, contributing to thrombus formation. Moreover, activated platelets release soluble CD40 ligand (sCD40L) which in turn contributes to oxidative imbalance, triggering the release of reactive oxidative species (ROS) on various cellular types. The aim of this work was to determine if the interaction between the oxidative response and platelet-derived sCD40L participates in the pathogenic mechanism during HUS. Activated human glomerular endothelial cells (HGEC) by Stx2 induced platelets to adhere to them. Although platelet adhesion did not contribute to endothelial damage, high levels of sCD40L were released to the medium. The release of sCD40L by activated platelets was inhibited by antioxidant treatment. Furthermore, we found increased levels of sCD40L in plasma from HUS patients, which were also able to trigger the respiratory burst in monocytes, in a sCD40L-dependent manner. Thus, we concluded that platelet-derived sCD40L and the oxidative response are reciprocally stimulated during Stx2-associated HUS. This process may contribute to the evolution of glomerular occlusion and the microangiopathic lesions.

Apoptosis and cell cycle arrest induction are targeted in the strategy of cancer therapy. Furthermore, bacterial toxin such as shiga-like toxin producing Escherichia coli has been suggested to be used as novel therapeutic agent against tumor malignancies either as independent anti-neoplastic agents or in combination treatment with chemo or radiotherapy. The aim of study was to investigate the potency of shiga-like toxin originated from local strains of E. coli O157:H7 as a new cancer therapy. As many as 10 culture cells T47D cell line were subjected by crude extract Shiga like toxin originated from five local isolates of E. coli O157:H7 i.e. KL-48(2), SM-25(1), SM-7(1), DS-21(4), and one isolate ATCC 43894 as a control with IC50 doses, respectively. The treatment was observed for 24 h, with two replications. An FITC-Annexin V and PI assay was used to observe apoptosis and necrosis effect, and simultaneously with cell cycle analysis using propidium iodide (PI) staining. Results of study showed T47D cell treated with Shiga-like toxin from local strain KL-48 (2) show the lowest viable cell, followed by SM 7(1), ATCC 43894, SM-25(1), DS-21(4) and contrary with control with each percentages as 15.20, 16.36, 22.17, 22.64, 33.86, and 94.36%, respectively. The results were also confirmed by the induction of the cell cycle arrest in phase G0-G1 as inactive phase, i.e. 66.41, 63.37, 61.52, 55.36 and 47.28% for T47D cell treated with toxin of KL-48(2), ATCC 43894, SM 25(1), SM 7(1), and DS 21(4), respectively. These results show tendency deleterious effect of Shiga-like toxin from local isolates on T47D cell, so that concluded they have potency as a good anticancer drug in Gb3-expressing breast cancer.

Shiga toxin-producing Escherichia coli (STEC) are notorious foodborne pathogens capable of causing severe diarrhea and other life-threatening complications in humans. Cattle remain a major reservoir and asymptomatic carriers of STEC. In reservoir animals, the rectoanal junction (RAJ) serves as the primary colonization site of STEC playing a critical role in its transmission to humans through contaminated food sources. However, the molecular mechanisms behind the adaptation of STEC in the RAJ of the asymptomatic reservoir host and its subsequent infection of human colonic epithelial cells in an event of a foodborne transmission to cause diarrhea remain largely unexplored. This study aimed to unravel the intricate dynamics of STEC O157:H7 serotype in these two distinct host environments: bovine RAJ cells and human colonic epithelial cells, during initial colonization. In this context, comparative transcriptomics analysis was employed to investigate the differential gene expression profiles of STEC O157:H7 during its interaction with these cell types. The bacterial cells were cultured under controlled conditions to simulate the microenvironments of both bovine RAJ and human colonic epithelial cells. Using high-throughput RNA sequencing, we identified key bacterial genes and regulatory pathways that were significantly modulated in response to each specific host environment. Our findings reveal distinct expression patterns of bacterial genes involved in virulence, including adherence, metal iron homeostasis and stress response in STEC O157:H7 grown in bovine RAJ cells as op-posed to human colonic epithelial cells six hours post-infection. Additionally, the comparative analysis highlights the potential role of certain genes in host adaptation and tissue-specific pathogenicity. Furthermore, this study sheds light on the potential factors contributing to the survival and persistence of STEC O157:H7 in the bovine reservoir, and its ability to colonize in-testinal epithelium and cause disease in humans.

(1) Background: Formation of biofilms on food-contact surfaces by Shiga-toxigenic Escherichia coli (STEC) can pose a significant challenge to the food industry, making conventional control-methods insufficient. Targeted use of bacteriophages to disrupt these biofilms could reduce this problem. Previously isolated and characterized bacteriophages (n=52) were evaluated against STEC biofilms in-vitro and on food-contact surfaces. (2) Methods: Phage-treatments (9 logs PFU/ml), in phosphate-buffered-saline, were used individually or as cocktails. Biofilms of STEC (O157, O26, O45, O103, O111, O121, and O145) were formed in 96-well micro-titer plates (7 logs CFU/ml; 24 h) or on stainless-steel (SS) and high-density-polyethylene (HDPE) coupons (9 logs CFU/cm2; 7 h), followed by phage-treatment. Biofilm-disruption was measured in-vitro at 0, 3, and 6 h as a change in optical-density (A595). Coupons were treated with STEC-serotype-specific phage-cocktails or a 21-phage cocktail (3 phages/serotype) for 0, 3, 6 and 16 h and surviving STEC populations enumerated. (3) Results: Of the 52 pages, 77% showed STEC-biofilm disruption in-vitro. Serotype-specific phage-treatments reduced pathogen population within the biofilms by 1.9-4.1 and 2.3-5.6 logs CFU/cm2, while the 21-pahge cocktail reduced it by 4.0 and 4.8 logs CFU/cm2 on SS and HDPE, respectively. (4) Conclusions: Bacteriophages can be used to reduce STEC and their biofilms.

Antimicrobial application of carbon nanomaterials such as carbon nanotubes (CNTs), capped CNT, C60 fullerene, and C70 fullerene are increasing owing to their low cytotoxicity properties compared to other nanomaterials such as metallic nanoparticles. Enhanced mechanical property and antibacterial activity can be caused by incorporation of CNTs in 3-dimentional (3D) printed nanocomposites (NCs). Interruption of bacterial membrane resulting from cylindrical shape and high aspect ratio properties has been found as the prominent antibacterial mechanism of CNTs. However, unraveling interaction of CNT, capped CNT, C60 fullerene, and C70 fullerene with virulence factors of the main bacterial pathogenesis has not yet been known. Therefore, in the present study, interactions of CNT, capped CNT, C60, and C70 with the eight virulence factors including protein kinase A and ESX-secreted protein B of Mycobacterium tuberculosis, pseudomonas elastase and exotoxin A of Pseudomonas aeruginosa, alpha-hemolysin and penicillin binding protein 2a of Staphylococcus aureus and shiga toxin 2a and heat-labile enterotoxin of Escherichia coli have been evaluated by molecular docking method of AutoDock Vina. This study disclosed the binding strength followed the sequence CNT > capped CNT > C70 > C60 towards alpha-hemolysin of S. aureus compared to other virulence factors with values of -19.6, -18.8, -13.6, and -12.8 kcal/mol, respectively. The lowest and highest binding affinity were found for CNT against 1TII and 1MWT by binding energy values of 97.4 and -20.1 kcal/mol. The stability of CNT-1MWT complex at the different times has resulted according to the normal mode analysis of elNémo and iMOD servers. Future studies should be focused on improving cellular uptake of CNTs, capped CNTs, C70, and C60 by surface functionalization for active targeting of bacteria.

Shiga toxins (Stxs), and more specifically the Stx2a subtype, are the major virulence factors involved in enterohemorrhagic Escherichia coli (EHEC)-associated hemolytic uremic syndrome (eHUS); a life-threatening disease causing acute kidney injury, especially in children. Cleavage of Stxs A subunit, when followed by reduction, boosts the enzymatic activity causing damage to targeted cells. This cleavage was assumed to be mostly mediated by furin during Stx intracellular trafficking. Cleavage of A subunit, without reduction, changes the binding properties of Stxs for blood components during HUS pathogenesis. To investigate whether the cleavage could occur in the intestine, even prior entering target cells, Stx2a structure was characterized after its exposure to specific host factors present in human stool. The structure of Stx2a A subunit was determined by immunoblotting after electrophoretic separation under reducing conditions. Trypsin and chymotrypsin-like elastase 3B (CELA3B), two serine proteases, were identified as potential candidates that may trigger the extracellular cleavage of Stx2a A subunit directly after its secretion by EHEC in the gut. Whether this observation indeed translates to natural infections and plays a role in eHUS pathogenesis has yet to be determined as well as whether host's protease profile could affect disease development by changing the toxin’s biological features.

O26 enteropathogenic Escherichia coli (EPEC), possesses a unique pseudocapsule composed of polysaccharides identical to the O antigen in their lipopolysaccharide (LPS) membrane. Therefore, the impact of O26 polysaccharides on the immune evasion mechanisms of capsulated O26 EPEC was investigated. Our findings reveal that the concentration of GlcNAc, an immunodominant unit of O26 polysaccharides capable of activating the MBL (Mannose Biding Lecting) pathway of the complement system, was found to be lower in capsulated EPEC O26 compared to naked shiga toxin-producing E. coli (STEC) O26 strain. It was noted that, unlike the naked STEC strain, the capsulated EPEC O26 strain was protected against lysis by the alternative pathway of the com-plement system by inhibiting C3b adhesion to its bacterial surface. Capsulated EPEC O26 strains were also able to avoid phagocytosis by macrophages. However, the immune evasion provided by the capsule was overcome in the presence of anti-O26 polysaccharide antibodies. Additionally, these antibodies were able to recognize O26 EPEC in the presence of biofilm and inhibit their adhesion to human epithelial cells. Overall, the results indicate that the O26 polysaccharides can generate an effective humoral immune response, making them promising antigens for the de-velopment of a vaccine against capsulated O26 E. coli