Serotypes, virulence genes and polymorphism of capsule gene cluster in Lactococcus garvieae isolated from diseased rainbow trout (Oncorhynchus mykiss) and mugger crocodile (Crocodylus palustris) in Iran

Background: Lactococcus garvieae causes lactococcosis in rainbow trout in many parts of the world. Aims: This study was conducted for the existence of the virulent factors and differentiation of the two serotypes in L. garvieae. Methods: Twenty-two strains of L. garvieae isolated from diseased rainbow trout from farms in different regions and mugger crocodile of Iran, were investigated. In order to rapidly detect the presence of the hly1, hly2, hly3, NADH oxidase, sod, pgm, adhPsaA, eno, LPxTG-3, adhCI, and adhCII virulence genes, two multiplex polymerase chain reaction (PCR) assays were developed. Also, simplex PCR method was used to identify the bacterial serotypes, CGC, LPxTG-2, Adhesion, and adhPav virulence genes using the specific primer. Results: All varieties of L. garvieae contained the hly1, hly2, hly3, NADH oxidase, pgm, adhPav, LPxTG-3, sod, eno, adhPsaA, adhCI, and CGC virulence genes. Also, adhCII gene was present in all strains except one of the isolates originated from mugger crocodile. In addition, LPxTG-2 gene was onlypresent in one of the isolates belonging to mugger crocodile. Adhesion gene was not present in all the strains. Interestingly, all the 22 strains originated from both hosts were identified as belonging to the serotype I. Based on the phylogenetic sequences of the capsule gene cluster, group all fish isolates into a cluster together with one isolate obtained from mugger crocodile. Conclusion: Further studies are recommended to investigate the role of virulence genes in L. garvieae and evaluate their pathogenicity to rainbow trout.