Drug resistance and pulsed-field gel electrophoresis patterns of Lactococcus garvieae isolates from cultured Seriola (yellowtail, amberjack and kingfish) in Japan

Aims: To investigate the existing antimicrobial susceptibility and genetic characteristics of Lactococcus garvieae isolates from cultured Seriola in Japan. Methods and Results: Minimum inhibitory concentrations (MICs) of 14 antimicrobial agents for 170 isolates were determined using the agar dilution method. Seventy-five isolates (44.1%) were simultaneously resistant to erythromycin (EM) (MIC >= 2 mu g ml(-1)), lincomycin (LCM) (MIC >= 128 mu g ml(-1)) and oxytetracycline (OTC) (MIC >= 4 mu g ml(-1)). Resistance to EM was grouped as intermediate- and high-level resistant by MIC values. All resistant isolates possessed ermB and tet(S) genes. The number of different bands between pulsed-field gel electrophoresis patterns of 25 isolates and two ATCC strains (isolated in 1974), determined using two enzymes (ApaI and SmaI), did not exceed 3. Conclusions: The present resistance pattern observed with ermB and tet(S) is similar to that observed in previous reports. Moreover, the genetic characteristics of L. garvieae isolates from a wide area in Japan in 2002 and ATCC strains were closely related. Significance and Impact of the Study: This study suggests that EM-, LCM- and OTC-resistant isolates have been present for 15 years and that L. garvieae strains with same origin have spread among Seriola spp. in Japan since 1974.