Virulence determinants and toxin profile of methicillin resistant Staphylococcus aureus from commercial cheese in Bangladesh: A public health risk

Abstract

Cheese, a widely consumed dairy product, can be contaminated with Staphylococcus aureus (S. aureus) , a pathogen capable of producing toxins harmful to humans. Of particular concern is Methicillin-Resistant S. aureus (MRSA), which harbors antimicrobial resistance genes and secretes super-antigenic toxins. Present investigation aimed at determining the occurrence and characterizing MRSA in commercial cheese, to evaluate its potential public health risks. 120 cheese samples representing twelve commercial brands were collected in ten different batches over a six-month period in Sylhet, Bangladesh. The quality of the cheeses was evaluated and compared against the standards of Bangladesh Food Safety Authority (BFSA), European Union (EU), and Food Safety and Standards Authority of India (FSSAI). The occurrence of MRSA and its virulence factors were determined using standard microbiological and molecular techniques. Results revealed that 65% samples were positive for S. aureus , with staphylococcal load surpassing safety thresholds according to the above-mentioned standards. MRSA was detected in 30% of the samples, exhibiting resistance to multiple antibiotics. All the isolates showed resistance against penicillin, tetracycline, doxycycline, trimethoprim-sulfamethoxazole and azithromycin, whereas ceftaroline, norfloxacin, and levofloxacin exhibited intermediate level of sensitivity. Enterotoxin genes SEa and SEc were prevalent in 16.67% and 8.97% of isolates, respectively, while TSST-1 gene was identified in 25.64% among the exfoliative toxin genes. Notably, 85.90% and 80.77% of the isolates exhibited biofilm formation based on the Congo Red and microtiter plate techniques, respectively, with significant percentages of biofilm associated regulatory genes icaA (73.08%), icaD (53.85%), clfA (78.21%) , clfB (61.54%) , and fnbA (69.23%). The substantial prevalence of bla CTX-M-2a (88.46%) and bla TEM (25.64%) highlights the significant public health risks associated with MRSA contamination in cheese. The high occurrence of S. aureus and the detection of multiple toxin-encoding genes further emphasize the need for strengthened monitoring and stricter control measures across the production and distribution chain to reduce contamination and ensure product safety.