Genetic diversity in Mycobacterium ulcerans isolates from Ghana revealed by a newly identified locus containing a variable number of tandem repeats.

The molecular typing methods used so far for Mycobacterium ulcerans isolates have not been able to identify genetic differences among isolates from Africa. This apparent lack of genetic diversity among M. ulcerans isolates is indicative of a clonal population structure. We analyzed the genetic diversity of 72 African isolates, including 57 strains from Ghana, by variable number of tandem repeat (VNTR) typing based on a newly identified polymorphic locus designated ST1 and the previously described locus MIRU 1. Three different genotypes were found in Ghana, demonstrating for the first time the genetic diversity of M. ulcerans in an African country. While the ST1/MIRU 1 allele combination BD/BAA seems to dominate in Africa, it was only rarely found in isolates from Ghana, where the combination BD/B was dominant and observed in all districts studied. A third variant genotype (C/BAA) was found only in the Amansie-West district. The results indicate that new genetic variants of M. ulcerans emerged and spread within Ghana and support the potential of VNTR-based typing for genotyping of M. ulcerans.