Antimicrobial activity, molecular typing and in vitro safety assessment of Lactococcus garvieae isolates from healthy cultured rainbow trout (Oncorhynchus mykiss, Walbaum) and rearing environment

Lactococcus garvieae is the aetiological agent of lactococcosis, an ichthyopathology affecting rainbow trout (Oncorhynchus mykiss, Walbaum) farming and having recently been considered as a potential food-borne zoo-notic agent. This work aims to characterise a population of 53 L. garvieae isolates from healthy cultured rainbow trout and rearing environment by using microbiological, biochemical and genetic assays to unveil the potential impact that their presence may have, not only for fish, but also for consumers. The lactococci exhibited a broad antimicrobial spectrum against Gram-negative ichthyopathogens, likely due to production of organic acids. The 53 L. garvieae isolates were grouped into two and five genetic clusters by PFGE and ERIC-PCR, respectively. All the lactococcal isolates produce alpha-haemolysis and harbour, at least, 10 putative virulence factors (hly-1, hly-2, hly-3, NADH oxidase, sod, pgm, adhPsaA, eno, LPxTG-3 and adhCI). While all the lactococci were resistant to streptomycin and clindamycin, no resistance genes were found. The manuscript concludes that the non-existence of active lactococcosis does not guarantee the absence of potentially virulent L. garvieae, which also exhibit a great capacity for adaptation and persistence in the environment. Furthermore, the antibiotic resistance profile shown may lead to re-evaluate the treatments of choice in human patients.

Automated summary

The study characterized a population of 53 L. garvieae isolates from healthy cultured rainbow trout and their rearing environment. The results revealed that these isolates exhibited antimicrobial activity against Gram-negative ichthyopathogens and carried multiple putative virulence factors. Additionally, the isolates showed resistance to certain antibiotics, highlighting the need to reevaluate treatment options for human patients.