Experimental Survival of Mycobacterium ulcerans in Watery Soil, a Potential Source of Buruli Ulcer

The reservoir of Mycobacterium ulcerans causing Buruli ulcer (BU) remains unknown. Here, sterilized watery soil was mixed with 2 x 10(6) colony-forming units (CFU)/g of M. ulcerans Agy99 or M. ulcerans ATCC 33728 and incubated in a microaerophilic atmosphere in the presence of negative controls. Both M ulcerans strains survived in soil for 4 months with a final inoculum of 300 110 CFU/g. Further, three groups of five mice with and without footpad scarification were exposed to control soil or M u/cerans-inoculated soil. Although no specific clinical and histopathological lesions were observed in control animals, red spots observed on 8/20 scarified feet in 8/10 challenged mice yielded inflammatory infiltrates and positive real-time polymerase chain reaction detection of M. ulcerans DNA in five mice. BU can be acquired as an inoculation infection with watery soil as a transient source of infection. These experimental observations warrant additional field observations.