In vitro Antimicrobial Susceptibility of Photobacterium damselae ssp. piscicida from Cobia (Rachycentron cannadum) at Penghu (Pescodores) Islands, Taiwan during 1999-2008

Abstract

Acute bacterial septicemic infection in sea cage-cultured juvenile cobia (Rachycentron cannadum) has occurred at Penghu (Pescodores) Islands, Taiwan, since October of 1999 with a 30-80% mortality rate. Diseased fish exhibited no apparent surface lesions; however, the kidney and spleen demonstrated swelling and white tubercles. The bacterium was identified as Photobacterium damselae ssp. piscicida, based on the results of the API-20E system and Bionor Mono-Pp kit. The pathogenicity of the isolate to cobia was confirmed by intraperitoneal injection and immersion. From histological examinations, multifocal necrosis and/or granulomatatous inflammation were found in tissue sections. Drug sensitivity testing indicated this pathogen were sensitive to amoxicillin, chloramphenicol, oxolinic acid, oxytetracycline, trimethoprim-sulfamethoxazole (SXT), and flumequine in 1999. However, amoxicillin-, chloramphenicol-, and oxytetracycline-resistant Photobacterium damselae ssp. piscicida were isolated in 2000. SXT-, oxolinic acid- and flumequine-resistant P. damselae ssp. piscida were isolated from sea cage-cultured cobia at Penghu in 2002, 2006, and 2007, respectively.1999年10月以後澎湖海水箱網養殖海鱺苗每年均感染急性出血性細菌性疾病，造成30-80%的死亡率。病魚無明顯外部病徵，但其脾臟及腎臟會腫大且出現很多白色小結節。以API-20E及Bionor Mono-Pp細菌鑑定系統，確定該病原菌為巴斯德桿菌Photobacterium damselae ssp. piscicida。菌液經由腹腔注射及浸泡感染均會造成死亡並出現相同病徵。組織病理觀察發現內臟組織出現多發性潰爛及／或肉芽腫。藥物敏感性試驗顯示1999年分離到的海鱺巴斯德桿菌對amoxicillin, chloramphenicol, oxolinic acid, oxytetracycline, trimethoprim-sulfamethoxazole (SXT)及flumequine都敏感。但2000年就分離到對amoxicillin, chloramphenicol及oxytetracycline產生抗藥性的巴斯德桿菌。之後分別在2002、2006、及2007年分離到對SXT、oxolinic acid、及flumequine產生抗藥性的巴斯德桿菌。