Quantitative PCR Assay for Mycobacterium pseudoshottsii and Mycobacterium shottsii and Application to Environmental Samples and Fishes from the Chesapeake Bay

Abstract

Striped bass (Morone saxatilis) in the Chesapeake Bay are currently experiencing a very high prevalence of mycobacteriosis associated with newly described Mycobacterium species, Mycobacterium pseudoshottsii and M. shottsii. The ecology of these mycobacteria outside the striped bass host is currently unknown. In this work, we developed quantitative real-time PCR assays for M. pseudoshottsii and M. shottsii and applied these assays to DNA extracts from Chesapeake Bay water and sediment samples, as well as to tissues from two dominant prey of striped bass, Atlantic menhaden (Brevoortia tyrannus) and bay anchovy (Anchoa mitchilli). Mycobacterium pseudoshottsii was found to be ubiquitous in water samples from the main stem of the Chesapeake Bay and was also present in water and sediments from the Rappahannock River, Virginia. M. pseudoshottsii was also detected in menhaden and anchovy tissues. In contrast, M. shottsii was not detected in water, sediment, or prey fish tissues. In conjunction with its nonpigmented phenotype, which is frequently found in obligately pathogenic mycobacteria of humans, this pattern of occurrence suggests that M. shottsii may be an obligate pathogen of striped bass.Mycobacteriosis is a common disease affecting a large variety of wild and aquacultured fishes worldwide (9). Chronic disease is most commonly observed and is characterized by granulomatous inflammation that may affect all host tissues. External clinical signs include scale loss, dermal ulceration, spinal defects, emaciation, and ascites (5,6,16,25,31).Mycobacteriosis in Chesapeake Bay striped bass (Morone saxatilis) was first observed in 1997 from histologic findings of acid-fast bacilli in granulomatous lesions (W. Vogelbein, unpublished data). Since the initial finding, surveys have demonstrated a very high prevalence of this disease in Chesapeake Bay striped bass, exceeding 50% in many samples (8,17). Concomitantly with detection of high prevalence, tag recapture analysis has indicated that natural, nonfishing mortality of Chesapeake Bay striped bass has increased since 1999 (13), and modeling of apparent prevalence data has indicated that some mortality is associated with disease (8). Because the striped bass is an ecologically and economically important finfish along the U.S. Atlantic coast, the high prevalence of this disease creates considerable concern about the continuing health of the resource.Mycobacteriosis of fishes has traditionally been considered to be caused by Mycobacterium marinum, M. fortuitum, or M. chelonae; however, the recognized diversity of Mycobacterium spp. infecting fishes has increased markedly in recent years (9).To date, neither M. fortuitum nor M. chelonae have been isolated from internal tissues of striped bass in the Chesapeake Bay, and M. marinum has been cultured from only a small fraction (3%) of fish (20). Instead, a variety of slow-growing mycobacteria have been isolated, dominated by the recently described species M. pseudoshottsii and M. shottsii (9,(20)(21)(22). The 16S rRNA gene sequenc...

Mycobacterial infection in Northern snakehead (Channa argus) from the Potomac River catchment

“…Pathogen screens among striped bass revealed infection with multiple mycobacterial species, including M. marinum , M. shotsii, M. pseudoshottsii (Gauthier et al . ). In many instances, infection levels exceed 70% in affected striped bass populations (Kaattari et al .…”

“…L41 and M. sp. L30 (poorly characterized isolates from striped bass) and M. marinum E11 were included in the alignment (Gauthier et al 2010). All alignments were performed using Geneious software v7.1.5 (Biomatters) using MUSCLE (Edgar 2004).…”

“…Mycobacterial infections in striped bass have been widely reported from the lower Potomac River, mainstem Chesapeake Bay, and lower reaches of other tidal tributaries of the Chesapeake Bay since the late 1990s. Pathogen screens among striped bass revealed infection with multiple mycobacterial species, including M. marinum, M. shotsii, M. pseudoshottsii (Gauthier et al 2010). In many instances, infection levels exceed 70% in affected striped bass populations (Kaattari et al 2005).…”

“…In general, mechanisms of transmission and dissemination of mycobacterial pathogens among fishes in the Chesapeake Bay watershed are largely undetermined, although Mycobacterium sp. have been isolated both directly from fishes and from the physical environment (water and sediment) in the region (Gauthier et al 2010). Should mycobacterial infection prove to be widespread among Northern snakehead regionally, the role of this species in Mycobacterium transmission to other fish species and potential implications for the geographic distribution of piscine mycobacteriosis in the Chesapeake Bay catchment would also warrant further investigation.…”

Spatiotemporal trends and drivers of fish condition in Chesapeake Bay

“…Direct hypotheses of disease transmission in the field remain difficult to test, although some etiologic agents are ubiquitously distributed in water of the bay mainstem (Gauthier et al 2010) and correlated to eutrophic conditions (Jacobs et al 2009). Therefore, elevated chl a may suppress striped bass condition through complex dynamics involving environmental effects on disease pathobiology.…”