Antimicrobial Activity, Antibiotic Susceptibility, and Growth Kinetics of Lactic Acid Bacteria and Yeasts Isolated from Selected Ugandan Cheese Varieties

Lactic acid bacteria (LAB) and yeasts constitute functionally important components of cheese microbiota, contributing to acidification, aroma formation, prolonged shelf life and microbial safety. This study investigated the antimicrobial activity, antibiotic susceptibility, and growth kinetics of LAB and yeasts isolated from selected ripened Ugandan cheese varieties in order to evaluate their suitability as starter or adjunct cultures. Isolates were identified through morphological, biochemical, and molecular approaches. Antimicrobial activity against Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa was assessed using agar well diffusion following established protocols. Antibiotic susceptibility was determined using disc diffusion in accordance with EUCAST and CLSI guidelines. Growth kinetics across pH gradients were monitored using a Bioscreen C automated microplate reader. The cheeses harbored diverse microbial communities, with considerable variation in antimicrobial activity among isolates. Pediococcus pentosaceus exhibited clear inhibition of S. aureus, whereas most isolates demonstrated limited antagonistic effects. Antibiotic susceptibility testing revealed multidrug resistance in Pediococcus acidilactici and in some opportunistic contaminants, emphasizing the need for careful safety assessments. Growth analysis showed that LAB grew optimally at moderately acidic pH (4.5–5.5), while Yarrowia lipolytica and Staphylococci preferred near-neutral conditions (pH 6.5–7.5). These findings highlight the presence of technologically valuable strains in Ugandan cheeses while underscoring the importance of antibiotic resistance screening in artisanal dairy systems. Select LAB strains, particularly P. pentosaceus and Lactiplantibacillus plantarum, show potential for starter culture development following genomic safety verification.