Fish and amphibians as potential reservoirs of Mycobacterium ulcerans, the causative agent of Buruli ulcer disease

Buruli ulcer is a skin disease associated with exposure to certain tropical water bodies. Much remains unknown about the reservoir and transmission of this disease. Previous studies have suggested that fish may concentrate M. ulcerans in their gills and intestines and then serve as passive reservoirs of the bacteria. The current study was designed to expand on earlier studies by using a PCR-based assay targeting the enoyl reductase (ER) domain of the plasmid responsible for mycolactone production to screen multiple species of fish and amphibians from multiple water bodies where M. ulcerans has been previously detected. This was done to test the hypothesis that fish and amphibians serve as natural reservoirs of M. ulcerans, with some taxa or feeding guilds being more likely to harbor the pathogen than others. ANOVA and non-metric multidimensional scaling showed no fish or amphibian species or feeding guild served as a reliable indicator of the presence of ER-positive mycobacteria in a water body. However, specimens from certain water bodies were observed to have higher ER-positivity rates than others. M. ulcerans in an adult frog was found and confirmed with VNTR analysis. This is the first reported finding of the bacterium in a wild adult amphibian and suggests that amphibians may warrant further study.