Newly identified Mycobacterium species in a Xenopus laevis colony.

The University of Massachusetts Medical School maintains 3 separate research colonies of Xenopus laevis, with each colony located in a separate building on campus. After a 5-wk in-house quarantine period, 34 wild-caught X. laevis were transferred into one of the existing colonies. As a result, this colony grew from 51 to 85 frogs. All animals were housed in a recirculating frog housing system. During the first 2 mo, 6 frogs died suddenly, and health reports were generated for another 10 frogs in this colony. The majority of health reports were written in response to acute coelomic distention. These patterns continued until, after 1 y, only 25 of the original 85 animals remained. Necropsies performed showed large accumulations of serosanguinous fluid in the subcutaneous space or body cavity. Granulomatous inflammatory lesions with acid-fast bacilli were generally present in the liver, lung, or spleen. Culture of affected tissues grew Mycobacterium sp. within 40 d. Polymerase chain reaction analysis confirmed the isolated organism to be the same species of Mycobacterium (provisionally named M. liflandii) recently reported by 2 other groups. However, previous clinical publications suggested that this bacterium originated only from X. tropicalis. The cases we present highlight the rapidly lethal effects of M. liflandii in a colony of wild-caught X. laevis and illustrate the need to dedicate further attention to this emerging Xenopus disease.