MOLECULAR DETECTION AND IDENTIFICATION OF GRAM-POSITIVE COCCI, STREPTOCOCCOSIS AGENT ISOLATED FROM RAINBOW TROUTIN MARKAZI PROVINCE

Aims and Streptococcosis is one of the most important diseases of the farmed fishes specially, rainbow trout, causing the death of many fishes and also leading to heavy damages on aquaculture centers. This research deals with the exact recognition and determination of Gram-positive cocci isolates (Streptococcosis agent), using PCR and sequencing analysis. the sampling was performed during spring and summer 2011 from 12 farms of Markazi province and 10 fish were selected with death-sick or clinical signs from each farm. Firstly the samples were cultivated in blood agar and incubated for 72 hours in 37˚C, then the conventional microbiology experiments were conducted on the suspected samples to confirm Streptococcosis disease. Also antibiogram test was carried out using disk diffusion method to determine the effective antibiotic type on known bacteria. All the positive microbial samples were subjected to PCR and sequencing experiments. In this research, 12 isolates of Gram-positive cocci were separated from kidney, brain, liver and spleen of 120 rainbow trout patients by microbiological and some biochemical tests. All positive microbial samples in PCR test (based on 16SrRNA gene) were recognized positive and determined as Lactococcus garvieae based on sequencing analysis. The resistance of gram-positive cocci to colistin, lincomycin, cloxacillin, streptomycin and nalidixic acid were shown on antibiograms disk diffusion experiment. Lactococcus garvieae is major gram-positive cocci in infected fish farms in Markazi province.