Phenotypic and genotypic characterization of pathogenic Staphylococcus spp. isolated from diseased Thai Koi (Anabas testudineus) in Bangladesh

Abstract

Thai Koi, Anabas testudineus is one of the dominant cultured species in aquaculture farms in Bangladesh. Due to recent imprudent intensification of aquaculture industry in Bangladesh, fish farms are suffering from emerging infectious diseases; while there have been limited studies on precise pathogen identification and disease treatment measures. Therefore, this study was aimed to perform phenotypic and genotypic characterization of coagulase-negative staphylococci (CoNS) isolated from diseased farmed Thai Koi (A. testudineus) in Bangladesh. Four isolates were collected from external lesions of diseased Thai Koi, and were presumptively identified as Staphylococcus sp. by Gram-staining, oxidase/catalase test, and growth in differential and selective media. Three (SEBCP-1, SEBCP-2 and SEBCP-3) and one isolate (SCBCP-1) were identified as S. epidermidis (SE) and S. capitis (SC), respectively based on their 16S rRNA gene sequences and polymerase chain reaction using a species-specific primer set. Disk diffusion susceptibility testing showed that, the isolates are all commonly resistant against antibiotics belonging to beta-lactam, tetracycline and quinolone class. All the isolates carried blaZ and efflux protein tet(K) gene responsible for resistant against β-lactam and tetracycline. In addition, all SE strains harbored mecA gene, suggesting that they might be accounted as methicillin resistant SE (MRSE). All four isolates caused mortality (66.66-100%) in carp challenged by intraperitoneal injection, indicating they are pathogenic in fish. Three S. epidermidis strains showed strong gelatinase, lecithinase, proteolytic and beta hemolytic activity, showing their roles as a potential virulence factor, S. capitis strain showed better biofilm formation activity it might be due to the presence of icaAB gene in it. Overall findings of this study shows that, CoNS could be a threat in Bangladeshi aquaculture, and thus further studies on disease monitoring, management and development on control measures should be carried out in the nearest future.