Elevated temperature inhibits Mycobacterium shottsii infection and Mycobacterium pseudoshottsii disease in striped bass Morone saxatilis.

Mycobacteriosis occurs with high prevalence in the wild striped bass Morone saxatilis of Chesapeake Bay, USA. Etiologic agents of mycobacteriosis in this system are dominated by Mycobacterium pseudoshottsii and Mycobacterium shottsii, both members of the M. ulcerans/M. marinum clade of mycobacteria. Striped bass occupying Chesapeake Bay during summer months where water temperatures regularly approach and occasionally exceed 30°C are thought to be near their thermal maximum, a condition hypothesized to drive high levels of disease and increased natural mortality due to temperature stress. M. shottsii and M. pseudoshottsii, however, do not grow or grow inconsistently at 30°C on artificial medium, potentially countering this hypothesis. In this work, we examine the effects of temperature (20, 25, and 30°C) on progression of experimental infections with M. shottsii and M. pseudoshottsii in striped bass. Rather than exacerbation of disease, increasing temperature resulted in attenuated bacterial density increase in the spleen and reduced pathology in the spleen and mesenteries of M. pseudoshottsii infected fish, and reduced bacterial densities in the spleen of M. shottsii infected fish. These findings indicate that M. pseudoshottsii and M. shottsii infections in Chesapeake Bay striped bass may be limited by the thermal tolerance of these mycobacteria, and that maximal disease progression may in fact occur at lower water temperatures.