Safety assessment, genetic relatedness and bacteriocin activity of potential probiotic Lactococcus lactis strains from rainbow trout (Oncorhynchus mykiss, Walbaum) and rearing environment

Abstract

This work reports the safety assessment, genetic relatedness and extracellular antimicrobial (bacteriocin) activity of 75 potential probiotic Lactococcus lactis strains isolated from aquacultured rainbow trout (Oncorhynchus mykiss, Walbaum) and rearing environment, and the biochemical and genetic characterization of the bacteriocin most active against the rainbow trout pathogen Lactococcus garvieae. Seventeen (22 %) strains produced, at least, one biogenic amine, but none of them amplified the corresponding genes. Thirty (40 %) strains showed antibiotic resistance to, at least, one antibiotic, and the only antibiotic resistance genes found were tet(K), tet(L), tet(O) and tet(T). None of the strains produced hemolysin or gelatinase, degraded gastric mucin or deconjugated bile salts. ERIC-PCR fingerprinting allowed clustering the lactococci in three well-defined and highly divergent groups (31.0 % similarity). Nine (12 %) L. lactis strains were identified as bacteriocin producers. The bacteriocin produced by L. lactis subsp. cremoris WA2-67 was purified, and mass spectrometry and DNA sequencing revealed its identity to nisin Z (NisZ). Altogether, the results allowed the identification of 34 (45.3 %) putatively safe lactococci, including three bacteriocinogenic strains. This is the first description of tet(K), tet(O) and tet(T) in L. lactis. Moreover, ERIC-PCR fingerprinting has been shown for the first time as a valuable tool for genetic profiling of L. lactis strains from aquatic origin. A NisZ-producing L. lactis strain has been isolated for the first time from an aquatic environment, and this strain may be considered as a potential probiotic for rainbow trout farming for improving the quality and safety of fish and fish products.