An epidemiological analysis of Nocardia seriolae isolated from a wide range of aquatic animals in Taiwan, based on their genotype and enzymatic activity

Abstract

Chronic disease following Nocardia seriolae infection in a wide range of aquatic animals has been reported in many Asian countries and recently in America and Mexico. This study aimed to investigate the epidemiological relationship among N. seriolae isolates in Taiwan by investigating their genotype and enzymatic activities. A total of 66 strains isolated from 14 known and four unknown host fish from five sites in Taiwan were characterized using five combined methods. High genotypic diversity was recognized among the isolates with 10 pulsotypes being identified from the pulsed‐field gel electrophoresis method and 21 reptypes from the repetitive extragenic palindromic amplification method; however, no natural plasmids were detected in this bacterial population. Pulsotypes A8 and RI analysed by PFGE and repPCR, respectively, were found to be predominant within five sites in Taiwan over 17 years of isolation. Enzymatically, the majority of isolates displayed high leucine arylamidase, β‐glucosidase and α‐glucosidase activities but were negative for lipase, α‐galactosidase, β‐glucuronidase, N‐acetyl‐glucosaminidase, α‐mannosidase and α‐fucosidase activities. We identified a strong association between genotype and enzymatic activity since the majority of pulsotypes displayed the same type of enzymatic profile. This study provides comprehensive and potential epidemiological data, which will aid the fish farming activities and prevention method development.

Pathogenicity characterization of nocardiosis in orange‐spotted grouper (Epinephelus coioides) via exposure to nine distinct isolates of Nocardia seriolae and four administrative routes

“…These networks ensure that the necessary virulence factors are produced and deployed by the organism during infection, regardless of genotypic variations. In our previous study, enzymatic activity (protease and aminopeptidase) was found to be strongly associated with these pulsotypes (Nguyen et al, 2023). These results indicate the possibility of genetic and enzymatic associations with N. seriolae virulence in orange‐spotted groupers.…”

“…Strain OT103003‐N11 (singleton A2), which was isolated in only one case of grey mullet Mugil cephalus in 2014, displayed noticeably low virulence in orange‐spotted grouper (40%). The unique genetic type of this isolate may be linked to its low virulence caused by low resistance to the host immune defences; this may explain why this strain is not well distributed among N. seriolae population from samples of 18‐year collection in our previous study (Nguyen et al, 2023). The original isolate OT105002‐AF15 (pulsotype A8) from grouper species was a predominant pulsotype in the PFGE analysis, causing repeatedly delayed mortality and long duration in both Trial 1 and 2.…”

“…Our previous genetic study found that this pulsotype A3 was widely distributed throughout pompano fish farms; moreover, various separate isolates from this host were genetically identical. Notably, the mild variation in the virulence of N. seriolae might be correlated to the original host species and pulsotypes (Nguyen et al, 2021).…”

“…Nine strains of N. seriolae , which represented nine pulsotypes by PFGE analysis in our previous study (Nguyen et al, 2023), were used to perform a pathogenicity test in orange‐spotted grouper by intraperitoneal injection (Table 1). Two replicates of five fish were considered in each challenged group and a control group.…”

“…Understanding the pathogenesis of nocardiosis in groupers is important for preventing the disease in aquaculture and developing a useful model for future nocardiosis prevention studies. Based on Pulse‐Field Gel Electrophoresis PFGE genotyping, we discovered a significant diversity of N. seriolae isolated from diseased fish in Taiwan (Nguyen et al, 2023; Shimahara et al, 2009). We hypothesise that genotype diversity may associate with bacterial pathogenicity in fish and that nocardiosis can occur in fish differently depending on the exposure route.…”