Mycobacteriosis in zebrafish colonies

Abstract

Mycobacteriosis, a chronic bacterial infection, has been as-sociated with severe losses in some zebrafish facilities and low-level mortalities and unknown impacts in others. The occurrence of at least six different described species (Myco-bacterium abscessus, M. chelonae, M. fortuitum, M. haemophi-lum, M. marinum, M. peregrinum) from zebrafish complicates diagnosis and control because each species is unique. As a generalization, mycobacteria are often considered opportun-ists, but M. haemophilum and M. marinum appear to be more virulent. Background genetics of zebrafish and environ-mental conditions influence the susceptibility of fish and progression of disease, emphasizing the importance of regu-lar monitoring and good husbandry practices. A combined approach to diagnostics is ultimately the most informative, with histology as a first-level screen, polymerase chain reac-tion for rapid detection and species identification, and cul-ture for strain differentiation. Occurrence of identical strains of Mycobacterium in both fish and biofilms in zebrafish systems suggests transmission can occur when fish feed on infected tissues or tank detritus containing mycobacteria. Within a facility, good husbandry practices and sentinel pro-grams are essential for minimizing the impacts of mycobac-teria. In addition, quarantine and screening of animals coming into a facility is important for eliminating the introduction of the more severe pathogens. Elimination of mycobacteria from an aquatic system is likely not feasible because these species readily establish biofilms on surfaces even in ex-tremely low nutrient conditions. Risks associated with each commonly encountered species need to be identified and in-formed management plans developed. Basic research on the growth characteristics, disinfection, and pathogenesis of zebrafish mycobacteria is critical moving forward.