Multidrug-resistant phenotypes among biofilm-producing staphylococcal isolates from farm-raised fish: a molecular scrutiny.

Aims: To describe the molecular characteristics of methicillin-resistant Staphylococcus aureus (MRSA) isolates from farm-raised fish.

Methods And Results: Fish samples (n = 180) collected from aquaculture farms in three major districts of Kerala, yielded 45 methicillin-resistant staphylococci (MRS) (25%) isolates. All of the isolates were resistant to tested beta-lactams, and 19 (42.22%) were resistant to flouroquinolones. According to the resistance profile of each isolate, 33 of 45 (73.33%) are identified as multidrug-resistant (MDR) isolates, with an average multiple antibiotic resistance (MAR) index of 0.41 ± 0.09. Notably, virulence determinants such as classical enterotoxin (sea & seb), and SE-like toxin (seg & sei) genes co-existed with Antimicrobial Resistance Genes (ARGs) in isolates studied. Regardless of the isolates being strong biofilm producers, only 23 (51.1%) harbored icaA and icaD genes. The heterogeneity of MRSA (n = 17) clones were evident as the species belonged to three major spa types (t345, t2526, and t1309) and sequence types (STs), viz., ST772, ST88, and ST672.

Conclusion: The current study on molecular characterization of the MRS isolates sheds light on the preventive measures that need to be implemented to limit the spread of AMR pathogens in aquaculture.