Detection of haemolysin genes as genetic determinants of virulence in lactococcus garvieae

Abstract

Haemolysin genes (hly1, hly2, hly3) are functional genetic determinants of virulence in bacterial pathogenesis. In this study, the presence of hly genes was investigated in Lactococcus garvieae, previously recovered from infected rainbow trout (Oncorhynchus mykiss) in commercial fish farms. Although the bacteriological phenotypic tests failed to correctly identify the six isolates at species level, the amplification products (1100 bp) of partial 16S rRNA gene region and their nucleotide homology confirmed that 21 isolates, including ATCC 43921 control, were L. garvieae. All strains carried hly2 (796 bp), while hly1 (522 bp) was carried by 20 strains, and hly3 (549 bp) by 16. The results suggested that hly1 and hly2 could directly participate in pathogenesis whereas hly3 might not be responsible for the strains’ virulence. Antibiogram tests indicated that all strains were susceptible to ampicillin while being resistant to clindamycin and streptomycin. Variations in resistance profiles against various antimicrobials were detected among strains. The detection of virulence genes coding for haemolysins and the determination of the antimicrobial resistance profiles might contribute to a better understanding of the mechanisms of virulence and resistance of L. garvieae, which may lead to the determination of new targets for therapeutics and vaccines against this pathogen.