Genetic Profiling of MRSA and MSSA from Food Contact Surfaces: Antibiotic, Heavy Metal and Benzalkonium Chloride Resistance

Staphylococcus aureus is a foodborne pathogen that affects animals and humans. The persistence of this pathogen in the environment is associated with its ability to form biofilms and/or develop resistance mechanisms to antibiotics and sanitizers. A total of 67 S. aureus strains collected from food contact surfaces (FCSs) made of stainless steel and FCS-polypropylene used in dairy industries in Jalisco, México, were selected for this study. The genetic diversity and genes indicating antibiotic resistance were determined using PCR; antimicrobial susceptibility, resistance to cadmium chloride (CdCl₂), and the minimum inhibitory concentration (MIC) of benzalkonium chloride (BC) were determined using the agar diffusion method and broth microdilution. Additionally, the effects of BC treatment on biofilm removal were evaluated. A total of 41.7% of the strains were MRSA [SCCmec Types II (20.8%), V (13.4%), and IV (7.4%)], and 58.2% were MSSA. Genes encoding antibiotic resistance—ermC (2.9%), ermA (2.9%), ermB (10.4%), aacA-aphD (10.4%), tetM (17.9%), and blaZ (88%)—were detected. A phenotypic test showed that 62.6% of the strains were cadmium-resistant S. aureus (>400 µg/mL CdCl₂), and the MICs of 97% of isolates lay between 1.56 and 25 µg/mL BC. Treatment with BC + MR (100 µg/mL + 1% milk residues) led to a smaller reduction in biofilm (2.11–2.25 log₁₀ cfu/cm²; p < 0.05) compared to BC (3.75–4.03 log₁₀ cfu/cm²; at 5–10 min). MSSA and MSRA can develop biofilms that harbor mechanism resistance-associated genes, which are a public health hazard and a food safety concern.