Virulence Determinants, Antimicrobial Resistance, and Biofilm Formation of Staphylococcus aureus Recovered from Ready-to-Eat Foods and Food Handlers in University Food Services

Staphylococcus aureus is a major food safety concern because of its ability to produce heat-stable enterotoxins, develop antimicrobial resistance, and express virulence factors associated with persistence and pathogenicity. The present study characterised S. aureus isolates recovered from ready-to-eat (RTE) foods and food handlers’ hands in university food service establishment in northern Portugal, focusing on virulence-associated genes, antimicrobial resistance profiles, and biofilm production. A total of 261 samples were analysed, including 156 RTE food samples and 105 hand swabs. Twenty-nine coagulase-positive staphylococci isolates were recovered and confirmed as S. aureus by detection of the nuc gene, corresponding to an overall prevalence of 11.11% (29/261). Of these, 20 isolates were obtained from food handlers’ hands and 9 from RTE foods. The hla and sei genes were detected in all isolates, while seg and tst were detected in 93.10%; sed was not detected. Biofilm-forming capacity was identified in 44.83% of isolates, with most strains exhibiting weak to moderate biofilm production. Resistance to at least one antimicrobial agent was observed in 31.0% of isolates, and presumptive methicillin-resistant Staphylococcus aureus represented 13.79%, all classified as multidrug-resistant. These findings support the occurrence of handling-related contamination and reinforce the need for strict hygiene practices, temperature control, and continuous monitoring in institutional food service environments.