Nested polymerase chain reaction assay for detection of Mycobacterium shottsii and M. pseudoshottsii in striped bass.

Wild striped bass Morone saxatilis in Chesapeake Bay are experiencing a high prevalence of mycobacteriosis, which produces granulomatous lesions of the skin and visceral organs. Culture-based studies have indicated that the newly described species Mycobacterium shottsii and M. pseudoshottsii are the dominant isolates from diseased fish. The classical fish pathogen M. marinum is also found, albeit at much lower frequencies. Both M. shottsii and M. pseudoshottsii are extremely slow-growing on standard selective media, and up to 12 months may be required for isolation and characterization. Epidemiological studies of mycobacteriosis in Chesapeake Bay would therefore benefit from rapid molecular assays with which to detect these species in fish. In this paper, we describe the development of polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assays capable of detecting M. shottsii, M. pseudoshottsii, and, in most instances, coinfections thereof in striped bass tissues. In addition, PCR-RFLP assays were designed to detect M. marinum and other as-yet-undescribed Mycobacterium spp. present in Chesapeake Bay striped bass. Comparison of these molecular assays with culture-based techniques using splenic tissue from wild striped bass yielded generally concordant results and demonstrated the applicability of these techniques to the study of wild fish.