Thursday, June 16, 2011

Progress on Mycobacterium

A recent paper on Mycobacteria presence in Chesapeake Bay, and its role in the production of disease in Striped Bass and humans came to my attention today

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.
Interesting. Aside from the methodology, which might as well be wizardcraft for all of my ability to understand it (I can follow the basics, but this is pretty fresh stuff), it seems they have found two species of Mycobacterium probably responsible for the majority of the myco in striped bass.

One of them (M. pseudoshottsii) is a clearly ubiquitous bug, found in virtually every water sample and mud sample, and most of the striped bass prey species they looked at. It's more common up the bay than down the bay, which might be related to pollution or salinity. More research needed. The miraculous thing is that everything isn't sick with it. It must not be horribly infective, or all the fish would be positive. It's asymptomatic in menhaden, so they may well be carriers, and sources of contamination.

The other (M. shottsii) is much rarer, (and also more difficult to analyze for), is not found in water, sediment or prey species, but solely in stripers. It's suggestive that it is an obligate pathogen on striped bass. This one (or a closely related version) may also be responsible for human myco infections.

Hat tip to Pax Fish.

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