Genotypic and phenotypic analysis of fish pathogen, Nocardia seriolae, isolated in Taiwan

Abstract The phenotypic and genetic characterizations of 92 isolates of fish pathogen Nocardia seriolae from grey mullet ( Mugil cephalus ), striped bass ( Morone saxatilis ), crimson snapper ( Lutjanus erythropterus ), sea bass ( Lateolabrax japonicus ), largemouth bass ( Micropterus salmoides ), grouper ( Epinephelus spp.), jarbua terapon ( Terapon jarbua ), snubnose pompano ( Trachinotus blochii ), and spotted scaf ( Scatophagus argus ) isolated in Taiwan during 1997–2007 were examined to investigate the epidemiological relationship among isolates. The phenotypic and genetic characterizations were determined by API ZYM and pulsed-field gel electrophoresis (PFGE) analysis, respectively. In the API ZYM test, N. seriolae were divided into alpha-glucosidase-positive and alpha-glucosidase-negative strains. The alpha-glucosidase activity was also investigated by inoculating N. seriolae in a medium containing substrate 4-nitrophenyl-alpha- d -glucopyranoside. Results of the alpha-glucosidase activity obtained by both methods indicate that all the strains had positive reaction with some exception. In PFGE analysis, digestions with restriction enzymes Xba I and Ase I produced 12 and 9 restriction patterns, respectively. The alpha-glucosidase positive strains were assigned to pulsotypes X1–10 and A1–7. Predominant pulsotypes X1 and A1 were obtained from > 79% of strains (73 and 78 strains of 92 strains by Xba I and Ase I, respectively), demonstrating a clonal dissemination of N. seriolae in Taiwan. On the other hand, alpha-glucosidase-negative strains were assigned to X11–12 and A8–9, which differed from those of alpha-glucosidase-positive strains in Taiwan.