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

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