Mycobacterium marinum and Fish and Frog Models of Infection

Abstract

Mycobacterium marinum is a natural pathogen of poikilothermic organisms including fish and frogs. In addition to M. marinum, M. fortuitum and M. chelonae subsp. abscessus can cause natural infection of poikilothermic animals including fish. From the viewpoint of the host, M. marinum infection in its natural hosts displays the characteristic immune hallmarks of giant-cell formation and granuloma formation that are seen in human tuberculosis. The development of two animal models, the goldfish, Carassius auratus, and the leopard frog, Rana pipiens, has provided the first natural-infection models for the study of mycobacterial pathogenesis. A relevant observation about the fish model is the similarity of the fish host response to M. marinum infection and the human host response to M. tuberculosis infection. Natural infection of reptiles and amphibians with M. marinum has not been systematically studied. Tadpoles, the developmental stage of the frog, were also susceptible to M. marinum infection. Thus, the frog model has been used to dissect the complex pattern of M. marinum gene expression in the granuloma, the site most likely to harbor M. marinum during the latent stage of infection. In summary, the fish and frog models of mycobacterial infection offer an opportunity to examine the interaction of a Mycobacterium species, M. marinum, with its host in natural infection models. The advantages in using the fish and the frog are that these models reflect a natural-infection model and, in comparison to other animal models, have a low cost.