Abstract

Infection with Mycobacterium marinum, M. chelonae and M. fortuitum causes a worldwide problem for the aquaculture industry. These species of mycobacteria can infect more than 150 species of fish. Until recently, the pathogenesis of these infections was unknown with the lack of genetic tools to investigate such pathogens on the molecular level. Our group had developed a novel model for studying the pathogenesis of fish mycobacteriosis as well as transposon mutagenesis system to identify novel virulence determinants. An interesting feature of our goldfish model is that, depending on the dose of M. marinum inoculated, we can elicit acute or chronic disease. The acute disease is induced by the injection of 10⁸ to 10⁹ CFU per fish, while the chronic disease is induced by the injection of 10² to 10⁷ CFU per fish. Systematic screening of a transposon mutant library of M. marinum led to the identification of 35 unique potential virulence factors. Thirty-three out of the 35 (94 %) loci have homologous genes in M. tuberculosis. In this short course, we will focus our discussion on the pathogenesis of fish mycobacteriosis with emphasis on the up-to-date information on methods for detection and control of such biothreat to the growing aquaculture industry.