Antimicrobial Resistance, Biofilms, and Toxin Profiles of Methicillin-Resistant Staphylococcus aureus in the Beef Value Chain of Bangladesh

Methicillin-resistant Staphylococcus aureus (MRSA), responsible for various foodborne illnesses, presents substantial hurdles throughout the beef value chain due to its ability to form robust biofilms and produce different types of superantigenic toxins. This study aimed to characterize biofilm-producing S. aureus isolated from raw beef and ready-to-eat (RTE) food samples collected from Gazipur and Dhaka City Corporations. A total of 240 samples were collected, with 120 from each city corporation, comprising 60 raw beef and 60 RTE samples. These samples were examined for colony forming unit (CFU) to assess the safety margin limit, as well as undergo screening for MRSA presence, antibiotic sensitivity testing through the Kirby–Bauer disc diffusion method, toxin profiling, and the characterization of biofilm-forming genes (icaA, icaB, icaC, and icaD). Finally, we performed a phylogenetic analysis to study the evolutionary relationship among strains. Results revealed the presence of S. aureus (nuc gene) in 167 out of 240 samples, with CFU counts surpassing safety thresholds within the One Health interfaces suggested by the Bangladesh Food Safety Authority (maximum limit for raw meat 10³ cfu/g and RTE 10² cfu/g). MRSA was detected in 40.83% of the total samples, all exhibiting resistance to several antibiotics. Positive isolates from both municipal corporations were completely (100%) resistant to oxacillin, ampicillin, and amoxicillin, yet demonstrated greater susceptibility to vancomycin (88.6%) and linezolid (34.1%). Additionally, Staphylococcal enterotoxin SEa was present in 45.79% of samples, followed by SEd (24.39%) and SEb (20.57%), while TSST-1 was present in only 2.81% of total samples. Again, it was observed that most of the isolates have biofilm formation capacity and harbored icaA (65%), icaD (61%), icaC (50%), and icaB (48%) biofilm-forming genes. The outcome of phylogenetic analysis revealed that our isolates have a close relationship with the isolates of blood samples from the United States. The findings highlight the critical need for enhanced food safety measures. Therefore, surveillance of MRSA in the beef value chain and the implementation of stringent hygiene practices are imperative to mitigate the risk of colonization and spread of MRSA strains that produce biofilms.