Genotype variation and stability of four variable-number tandem repeats and their suitability for discriminating strains of Mycobacterium leprae

ABSTRACT

It has not been possible to distinguish different strains of Mycobacterium leprae according to their genetic sequence. However, the genonme contais several variable-number tandem repeats (VNTR), which have been used effectively in strain typing of other bacteria. To determine their suitability for differentiating M. leprae, we developed PCR systems to amplify 5 different VNTR loci and examined a battery of 12 M. leprae strains derived from patients in different regions of the United States, Brazil, Mexico, and the Philippines, as well as from wild armadillos and sooty mangabey monkey. We found diversity at for VNTR (D = 0.74), butone system (C16G8) failed to yield reproducible results. Alleles for the GAA VNTR varied in length from 9 to 12 copies, andthose for AT17 varied in length from 13 to 20 copies. Relatively little variation was seen with interspecies transfer of bacilli or during short-term passage of strains in nude mice or armadillos. The TA18 locus was more polymorphic than other VNTR, and genotypic variation was more common after long-term expansion in armadillos. Most strain genotypes remained fairly stable in passage, but atrain Thai-53 showed reamrkable any particular genotype associable with different regions or hosts of origen. VNTR polymorphisms can be used effectively to discriminate M. leprae strains. Inclusion of additional loci and other elements will likely lead to robust typing system that can be used in community-based epidemiological studies and select clinical application