한국에서 분리된 Edwardsiella piscicida 균주의 혈청형 관련 유전자 및 레지스톰 분석

Abstract

Although Edwardsiella piscicida is an important pathogenic bacterium in the aquaculture industry, comprehensive studies on serotype and analysis of resistome have not been conducted to date. Therefore, the aims of this study were to identify key antigen-related genes for molecular serotyping and investigate resistome of E. piscicida to determine the most effective antibiotics and to obtain data that can be used for future resistance gene monitoring. In this study, antigen-antiserum agglutination test were conducted on 46 E. piscicida strains isolated in Korea. Using the genome of E. piscicida, total 132 genes were identified to be associated with antigenicity. Protein sequence of these genes were compared and multilocus sequence typing (MLST) was conducted using seven genes(fepE, glycosyltransferase, wzzB, phoP, capsule associated glycosyltransferase, flgL and motB) with different protein sequence homology by host. Minimum inhibitory concentration (MIC) test against eight antibiotics (amoxicillin, cephalexin, ceftiofur, oxytetracycline, florfenicol, oxolinic acid, enrofloxacin and trimethoprim/sulfadiazine) was applied to 199 E. piscicida strain isolated in Korea. A resistome analysis was conducted using genomes, and PCR was performed to confirm the existence of antibioitc resistance genes on 199 strains isolated from Korea. As a results, antigen-antiserum agglutination tests revealed variations in titers between olive flounder and eel-derived strains. In genomic analysis, there were differences of protein sequence homology in seven genes. Importantly, results of MLST using these seven genes are confirmed the clustering of strains based on their host origin. The MIC results showed E. piscicida have high level of resistance in oxytetracycline and trimethoprim/sulfadiazine. Similar to the phenotypic results, tet gene, dfr and sul genes were most frequently detected in E. piscicida (55.8%, 57.2%). Recent isolates (2017-2022) exhibited an increased NWT ratio for penicillin antibiotics and all strains that have blaTEM-10 or blaOXA-10 were NWT against amoxicillin. All NWT strains for oxolinic acid, a quinolone antibiotic, were eel-derived and this strains have mutation in ParC(S84I, S84R). In conclusion, these finding provide valuable insights into the serological characteristics and antibiotic resistance of E. piscicida isolated from Korea, contributing to the development of effective defense strategies(e.g. antibiotics and vaccine) against this pathogen in the aquaculture industry.