Isolation and characterization of Lactococcus garvieae from diseased rainbow trout ( Oncorhynchus mykiss , Walbaum) cultured in Iran

Abstract

Summary A total of 200 moribund rainbow trout with clinica l signs of a hyperacute haemorrhagic septicemia wer e collected from rainbow trout farms in Fars, Kohkilo yeh-Boyer Ahmad and Charmohal-Bakhtiari provinces in the south and southwest of Iran during summer 2002 to winter 2008 for detection of Lactococcus garvieae , the causative agent of lactococcosis. Fish kidney s amples were cultured aseptically onto brain heart i nfusion agar plates and incubated at 25°C for 48 h. Using c onventional biochemical tests, L. garvieae was detected from 32 fish (16% of total fish samples). Additiona lly, isolates were confirmed as L. garvieae using a specific PCR assay based on 16S rDNA gene by producing a single band of 1107 bp. Partial analysis of 1 6S rDNA revealed 100% sequence similarity for all Iran ian isolates and there was a close genetic relation ship among these isolates and those previously reported from mullet in Taiwan (AF352166) and yellowtail in Japan (AB267897) based on GenBank data. Results of antibiogram tests on L. garvieae isolates showed a high susceptibility to erythromycin, enrofloxacin, chloramphenicol and clarithromycin. In pathogenicit y tests, immersion of fish in a bacterial suspension of 6 ◊ 10 5 colony forming unit/ml of L. garvieae in challenge experiments showed 60% mortality during 14 days post-infection. Experimentally, infected fis h showed typical blackening of skin haemorrhages, exophthalmia and wide haemorrhages on viscera. The present study provides useful molecular and biochemical information for L. garvieae isolates in Iran compared with those from different hosts and geogra phic locations.