Characterization of <i>lsa</i> (D), a Novel Gene Responsible for Resistance to Lincosamides, Streptogramins A, and Pleuromutilins in Fish Pathogenic <i>Lactococcus garvieae</i> Serotype II
Yin‐Ze Shi, Terutoyo Yoshida, Atushi Fujiwara, Issei Nishiki
Abstract
Aims: Fish pathogenic Lactococcus garvieae serotype II has been isolated from cultured fish species in Japan. This study aimed to investigate the molecular mechanisms of lincomycin (LCM)-resistant L. garvieae serotype II and assess the molecular basis for lincosamides–streptogramins A–pleuromutilins (LS A P)-resistant phenotype. Results: We identified a novel lsa (D)-encoded 497-aa ATP-binding cassette F (ABC-F) protein in the LS A P-resistant strains. Amino acid identities of 41.25–54.73% were obtained between the deduced amino acids from Lsa(D) and other Lsa-type ABC-F proteins. Furthermore, comparative analysis revealed that the allele of lsa (D) with single point mutation at 233 aa position (T G G → T A G; tryptophan→premature termination codon [PTC]) in LS A P-sensitive strains. The minimum inhibitory concentrations of antimicrobials against the lsa (D) complementary strain and lsa (D)-disrupted mutant confirmed that lsa (D) conferred the LS A P-resistant phenotype. The reverse transcription–polymerase chain reaction could not detect the noncoding region of lsa (D) allelic variant in the LS A P-sensitive strains. Additionally, the PTC (TAG) in LCM-sensitive strains was replaced by T G G, C AG, or TA T in the laboratory-induced revertant mutants. Conclusions: The novel lsa (D) conferred the LS A P-resistant phenotype in clinically LCM-resistant L. garvieae serotype II strains. However, the allele of lsa (D) gene containing the PTC was found in L. garvieae serotype II, resulting in the LS A P-susceptible phenotype.