ISOLATION OF MYCOBACTERIUM-ABSCESSUS FROM JAPANESE MEDAKA

Japanese medaka Oryzias latipes were cultured at the U.S. Army Biomedi cal Research and Development Laboratory for use as aquatic toxicity te st animals. During routine histological examination, granulomatous les ions were detected, and a low prevalence of Mycobacterium sp. was susp ected in the culture system. Fish maintained under experimental and br eeding conditions were cultured for acid-fast bacteria. Modified Middl ebrook 7H10 medium with albumin, dextrose, and catalase (ADC) enrichme nt was used to recover mycobacteria from whole-fish homogenates via th ree isolation procedures. Highest isolation rates were obtained by sub merging whole fish in individual bags of modified broth at a 1:10 (wei ght:volume) dilution for 1 h, then homogenizing the whole fish and pla ting diluted samples on solid medium using a plate count method. Medak a, ranging in age from 2 to 27 months, were positive for Mycobacterium abscessus with prevalences of 25%-100%. Mean bacterial counts for all groups examined ranged from 6.7 x 10(2) to 4.5 x 10(8) colony-forming units per gram of fish. Throughout the study, fish remained apparentl y healthy, exhibited no clinical signs of piscine mycobacteriosis, and suffered no significant mortality.