Isolation and Characterization of Lactococcus garvieae from Diseased Rainbow Trout (Oncorhynchus mykiss, Walbaum) Cultured in Northern Iran Based on the Nucleotide Sequences of the 16s rRNA

This study was done to determine the molecular and biochemical identification of some causative agents of lactococcosis in farmed rainbow trout in Mazandaran provenience (northern Iran). A total of 200 moribund rainbow trout, suspected of lactococcosis from 10 rainbow trout farms in Mazandaran province, were collected during spring 2012 to winter 2012. Sampling was done from the kidney, spleen, liver and brain and cultured aseptically onto brain heart infusion (BHI) agar plates and incubated at 25 °C for 24- 48 h. Results of bacteriological cultures of these organs showed 19 % Lactococcus garvieae (38 fish), 9 % Streptococcus spp., (18 fish), 17 % Yersinia spp. (36 fish), and 55 % of fish were culture negative. The PCR assay was developed based on the 16s rRNA gene of L. garvieae for the rapid and specific detection and identification of this pathogen from different sources. Two pairs of primers were designed based on the nucleotide sequences of the 16s rRNA gene of L. garvieae. After PCR assay on isolated bacterial colonies, DNAs extracted from 38 L. garvieae gave the expected 1107 bp PCR fragment of 16S rDNA sequences, which is specific for L. garvieae. The results of this study suggest the use of molecular methods along with current biochemical methods are effective diagnostic tools in the identification of L. garvieae. The combination of these methods for diagnosis of other bacterial disease i