DETECTION OF NON-GRANULOMATOUS LESIONS OF MYCOBACTERIUM SPECIES IN CULTURED FRESHWATER HYBRID STURGEON

摘要

A disease outbreak with 71% (cumulative) mortality was reported in a freshwater hybrid sturgeon farm located in Hualien County, Taiwan. The moribund fish showed signs of lethargy, anorexia, diffuse external hemorrhages around mouth and anus, and on the base of fin and abdomen surface accompanied with abdomen swelling. Post-mortem examination revealed multiple red patches ranging from 1 to 5 cm in size on the liver. The histopathology revealed extensive coagulative to liquefied necrosis of various sizes in the liver and spleen. Focal necrosis of kidney was also evident. The lesions were positive with Ziehl-Neelsen acid fast staining. A rapid growth of nontuberculous mycobacteria (NTM) was isolated from liver of moribund sturgeon and the polymerase chain reaction (PCR) studies using primer sets derived from Mycobacterium sp. suggested this NTM was closely related to Mycobacterium marinum. There was only one bacterial colony been isolated in brain heart infusion agar (BHI Agar) and been identified asStreptococcus iniae. These findings suggest that a bacterium identified as belonging to M. marinum might cause heavy mortality.