Extracellular products from Mycobacterium spp in fish

Mycobacterium spp. isolated from food and ornamental fish in Thailand (TB1, TB40, TB267 and TB268), and the type strains Mycobacterium marinum (NCIMB 1298), M. fortuitum (NCIMB 1294) and M. chelonae (NCIMB 1474) were cultured in Long's medium, Eagle's minimum essential medium, Sauton's medium and modified Sauton's medium. The latter enabled excellent growth and production of extracellular products (ECP) from TB 40, TB267, TB268 and M. marinum NCIMB 1298 in particular, whereas growth and production of ECP for all strains was limited in Long's medium. SDS-PAGE protein profiles of ECPs from 14-day culture supernatants showed major bands at 65 and <14 kDa. After 2 days culture at the higher temperature of 37 degrees C (heat shock), the production of ECP from all mycobacteria strains except M. marinum averaged approximately four- to 10-fold higher than from strains cultured for 14 days at 28 degrees C. Enzyme testing for the type strains indicated only mucinase activity for M. marinum, while lipase and RNase activities were detected for M. chelonae and M. fortuitum. Protease and DNase activities could not be detected for any of the Mycobacterium spp. tested. The medium lethal dose (LD(50)) of ECP to rainbow trout and Nile tilapia was greater than 400 mu g protein fish(-1).