넙치, Paralichthys olivaceus 의 에드워드병 및 연쇄구균병 원인체의 항생제 감수성 패턴과 질병 치료 효과 연구

Abstract

Edwardsiellosis and streptococcosis lead to serious economic losses in aquaculture industry. Use of antibiotics to control bacterial infection is still a common method, although commercial vaccines are available in recent years. However, there is no interpretive criteria to distinguish susceptible from resistant strains of most fish pathogens, including E. tarda and S. parauberis, and also specified effective therapeutic regimes against these diseases. Therefore, the aims of this study were to generate epidemiological cut-off (ECOFF) values of 52 strains of E. tarda and 48 strains of S. parauberis using normalized resistance interpretation (NRI) analysis, and determine the most effective chemotherapeutic methods in in vivo. Disc diffusion method was applied to all bacterial strains used in this study. Polymerase chain reaction was conducted to confirm the existence of antibiotics resistance related genes in E. tarda. For efficacy test, florfenicol was used orally to treat edwardsiellosis in olive flounder (Paralichthys olivaceus). For streptococcosis, amoxicillin and florfenicol were used by means of oral and intramuscular injection method. Valid ECOFF values were calculated for species/antibiotic combinations. Wild type proportion of E. tarda against florfenicol and S. parauberis against amoxicillin and florfenicol was the highest Most E. tarda strains classifed as non-wild type harbored antibiotic resistance related genes, such as sulfonamide (sulⅠ, sulⅡ, sulA), trimethoprim (dfrA5, dfrA7, dfrA12), tetracycline (tetA) and florfenicol (floR). Oral treatment with 15 mg/kg of body weight for 10 consecutive days was most effective, and intramuscular injection with amoxicillin at a dose of 40 mg/kg of b.w. appeared to be most effective antibiotic therapy against streptococcosis. Most ECOFF values generated in this study were valid as standard deviation values were reasonably low and the number of wild type was enough. Also, possession of some antibiotic resistance related genes were correlated with classification of isolates as non-wild type. Therefore, if an isolate was categorized as non-wild type with respect to an agent, it would be very reasonable to use that agent for therapeutic purpose. This study contains most valuable data related to antibiotic therapy, which have not been previously presented elsewhere and will contribute to develop in this field.