Phenotypic and genotypic evaluation of resistance to broad - range antimicrobial drugs in Gram- positive cocci isolated from rainbow trout in Ilam

Streptococci and lactococci are among bacterial diseases of wild and farmed fish especially rainbow trout and accounted for significant economical losses in the aquaculture industry. In this study, 60 fish from rainbow trout farms in Ilam, were collected and sampled for bacterial and molecular analyses. Identification of the isolated bacteria was determined using biochemical tests and confirmed by polymerase chain reaction (PCR). For this purpose, using primer sets targeting portions of the tuf (code along factor Tu) and 16S rRNA gene sequences were performed to determine the genus Streptococcus and Streptococcus iniae, respectively. In total, 110 isolates belonging to the genus Streptococcus, Lactococcus and Staphylococcus were detected. Molecular tests showed that 90 isolates were Streptococcus genus, of which 35 isolates tested by species-specific primers were identified as Streptococcus iniae and the rest (55 isolates) belonged to the species Lactococcus garvieae. Subsequently, phenotypic and genotypic evaluations of antibiotic-resistance of the isolates were performed, using disk diffusion method and PCR targeting tet, erm and str genes. The results showed that of the 110 isolates of Gram-positive cocci, 39 isolates were resistant against streptomycin (35%), 26 to erythromycin (23%), 35 to oxytetracycline (31%), 30 to enrofloxacin (27%), 21 to florfenicol (19%) and 33 isolates were resistant to penicillin G (30%). The presence of streptococcosis / lactococcosis was confirmed among fish farms in Ilam within this study. Moreover, it seems that the indiscriminate use of antibiotics has led to stablish resistant against such infectious agents.