Antimicrobial Resistance and Biofilm Formation in Staphylococcus Aureus Isolated from Retail Meat: Implications for Food Safety

Staphylococcus aureus is a significant pathogen that can be transmitted through the food chain, often linked to antimicrobial resistance (AMR) and virulence factors, which contribute to its persistence and pathogenicity. Biofilm formation enhances its survival under adverse conditions and contributes to AMR dissemination. This study aimed to evaluate the antimicrobial resistance profile and biofilm formation of S. aureus strains isolated from meat samples and its implications for food safety. Seventy-five meat samples, including fresh meats and meat-based products, were collected in Northern Portugal. S. aureus strains were isolated and antimicrobial resistance was determined using the Kirby–Bauer disk diffusion method, against 14 antimicrobial agents. Resistance and virulence genes were evaluated by PCR. All samples were tested regarding their biofilm formation using the microtiter biofilm assay at 24 and 48 hours. Biofilm biomass quantification was performed via Crystal Violet staining. The results were normalized against the reference strain S. aureus ATCC® 25923 to ensure consistent comparison S. aureus isolates were resistant to penicillin (52.6%), tetracycline (44.4%), chloramphenicol (36.8%) and tobramycin (26.3%). Resistance genes found were: tetK (31.58%), cat_pc223 (21.05%) and blaZ and ant(a’)-Ia (15.79%). All isolates demonstrated the ability to form biofilms at both 24 and 48 hours. Biofilm production was lower at 24 h, with a percentage mean of 114.34% ± 12.51, when compared to 48 hours, where it increased to 115.04% ± 22.43. However, these differences were not statistically significant (p > 0.05). Additionally, our isolates showed a higher biofilm production capacity when compared to the reference strain used. These findings highlight the public health risks posed by food-adapted S. aureus, particularly their role in promoting bacterial survival through biofilm formation, and AMR in food environments, emphasizing the need for targeted strategies to mitigate these risks in the food industry.