Comparison of Lactococcus garvieae strains isolated in northern Italy from dairy products and fishes through molecular typing.

Aims: To investigate the genetic relatedness between Lactococcus garvieae strains isolated from fish and dairy samples collected in northern Italy, using random-amplified polymorphic DNA (RAPD)-polymerase chain reaction (PCR), Sau-PCR and amplified fragment length polymorphism (AFLP). Methods and Results: Eighty-one isolates from bovine and caprine dairy products (n = 53) and from diseased rainbow trouts and other fishes (n = 28) were examined. All methods showed a typeability of 100%, repeatability ranging from 84.4% to 97.5% and discriminatory powers from 0.798 to 0.986. Dairy and fish strains revealed a low genetic relatedness as they are often grouped into distinct clusters. RAPD analysis discriminated 52 genotypes when primer M13 was used, whereas with primer P5 only 27 genotypes were identified. When Sau-PCR was performed, 13 genotypes were detected while AFLP analysis allowed the differentiation of 32 genotypes. Conclusion: L. garvieae strains isolated from dairy samples are generally not related to those collected from fish lactococcosis outbreaks. Significance and Impact of the Study: L. garvieae strains exhibit a genetic diversity related to the specific animal host they colonize. RAPD M13 fingerprinting proved to be a molecular tool for comparing isolates, whereas Sau-PCR and AFLP analyses were useful techniques to investigate the distribution of L. garvieae populations in the environment.