Diagnosis and management of atypical Mycobacterium spp. infections in established laboratory zebrafish (Brachydanio rerio) facilities

Two established zebrafish colonies experienced increased mortality and decr eased reproductive performance. Initial examination of several fish from on e facility revealed hyperemic gills, petechia around the opercula, abdomina l distention, and emaciation, Affected fish had congested liver with inflam mation and multifocal hepatic necrosis, Large numbers of acid-fast-positive , rod-shaped bacteria were evident in multiple tissues and the blood. Mycob acterium fortuitum was subsequently isolated from several fish. Zebrafish f rom the second facility had skin erosions and ulceration along the flank ju st caudal to the pectoral fins, Large numbers of acid-fast-positive, rod-sh aped bacteria were observed within the necrotic centers of well-demarcated, multifocal granulomas in gonads, liver, and peritoneum from affected fish. Mycobacterium abscessus and M. chelonae were isolated and identified bioch emically. Definitive diagnosis in these outbreaks was obtained by culture o n selective media. Because Mycobacterium spp, grow extremely slowly and pos itive confirmation may require 45 to 60 days, Mycobacterium species-specifi c polymerase chain reaction analysis was used to provide a rapid screening assay for Mycobacterium spp, as well as for verification of culture results . To our knowledge, this is the first documentation of mycobacterial infect ion in laboratory-maintained zebrafish and provides guidelines for diagnosi s, management, and prevention of atypical mycobacteriosis in laboratory zeb rafish colonies.