Mycobacteriosis in Zebrafish Colonies

Abstract

Mycobacteriosis, a chronic bacterial infection, has been associated 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 (Mycobacterium abscessus, M. chelonae, M. fortuitum, M. haemophilum, M. marinum, M. peregrinum) from zebrafish complicates diagnosis and control because each species is unique. As a generalization, mycobacteria are often considered opportunists, but M. haemophilum and M. marinum appear to be more virulent. Background genetics of zebrafish and environmental conditions influence the susceptibility of fish and progression of disease, emphasizing the importance of regular monitoring and good husbandry practices. A combined approach to diagnostics is ultimately the most informative, with histology as a first-level screen, polymerase chain reaction for rapid detection and species identification, and culture 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 programs are essential for minimizing the impacts of mycobacteria. 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 extremely low nutrient conditions. Risks associated with each commonly encountered species need to be identified and informed management plans developed. Basic research on the growth characteristics, disinfection, and pathogenesis of zebrafish mycobacteria is critical moving forward.

Recommendations for Health Monitoring and Reporting for Zebrafish Research Facilities

“…Realtime PCR offers significant advantages for detection of Mycobacterium spp., which are slowing growing bacteria and often require special conditions for growth. 25 Bacterial culture can facilitate isolation and species-level identification of a wide array of microorganisms, including bacteria, yeast, filamentous fungi, and oomycetes. Sensitivity of microbiology for zebrafish varies according to the biology of the organisms cultivated and the experience of the laboratory with aquatics, since several fish pathogens have specific requirements, including unique incubation temperatures, specialized culture media, and/or longer incubation times.…”

“…There are more than 170 recognized Mycobacterium spp., including both infectious and noninfectious environmental species, which may be found in zebrafish systems and have the potential to cause disease in fish and/or human handlers. [25][26][27] Immunosuppressed handlers are particularly at risk. Seven different species have been reported to be pathogenic in zebrafish, including M. chelonae, M. marinum, M. haemophilum, M. abscessus, M. fortuitum and M. peregrinum and M. saopaulense.…”

“…Seven different species have been reported to be pathogenic in zebrafish, including M. chelonae, M. marinum, M. haemophilum, M. abscessus, M. fortuitum and M. peregrinum and M. saopaulense. 25,26 These mycobacterial species are facultative pathogens that can both proliferate in the system biofilms and infect immunocompetent zebrafish. 25,27 Two of these, M. marinum and M. haemophilum, are slowly growing mycobacteria that cause obvious clinical disease and mortality in infected colonies.…”

“…25,26 These mycobacterial species are facultative pathogens that can both proliferate in the system biofilms and infect immunocompetent zebrafish. 25,27 Two of these, M. marinum and M. haemophilum, are slowly growing mycobacteria that cause obvious clinical disease and mortality in infected colonies. 25,28 The five remaining species are all rapidly growing mycobacteria in culture.…”

“…25,27 Two of these, M. marinum and M. haemophilum, are slowly growing mycobacteria that cause obvious clinical disease and mortality in infected colonies. 25,28 The five remaining species are all rapidly growing mycobacteria in culture. M. chelonae is the most widely distributed and prevalent mycobacterial infection of zebrafish.…”