Prevalence of virulent and biofilm forming ST88-IV-t2526 methicillin-resistant Staphylococcus aureus clones circulating in local retail fish markets in Assam, India

The burden of antimicrobial resistance (AMR), particularly in India has been increased alarmingly. Methicillin-resistance in Staphylococcus aureus has been recognized as serious threat to the human especially if they are biofilm forming and equipped with virulence factors. In the present study monitoring of antibiotic resistant S. aureus was performed at three selected sites in Assam, India in August 2019 and February 2020. Ethnographic information was collected from the fish vendors in order to track and address potential sources of contamination. Twenty three potential methicillin-resistant S. aureus (MRSA) strains were identified from fish sold by these vendors and subjected to molecular characterization. The antimicrobial resistance profile of these MRSA strains were regarded as multidrug-resistant (MDR) as they were resistant to ≥3 classes of antibiotics. The most prevalent resistance profile was; ampicillin-cefazolin-cefoxitin-gentamicin-norfloxacin-oxacillin-penicillin. Accessory gene regulators III (agr III) type MRSA (18/23, 78.26%) were found to be predominant compared to agr I type (5/23, 21.74%). Four isolates (17.39%) were observed to carry SCCmec-IV elements, which is a typical feature of community-associated MRSA (CA-MRSA). Two SCCmec-IV MRSA isolates were found to harbour panton-valentine-leucocidin (PVL) toxin genes and were resistant to macrolide in addition to beta-lactams. MLST and spa typing identified all MRSA as ST88 with spa type t2526. This is the first report from India on the incidence of ST88-SCCmec-IV (ST88-IV) MRSA in a fish market and its aquatic environs. The high prevalence of a single MLST clone, ST88, suggests that this lineage has a unique survival advantage in this environment. The study discusses the contribution of hospital wastewater in the dissemination of pathogenic MRSA clones to aquatic resources and then to humans through the food chain.