Introduction: Leprosy is a chronic disease caused by infection with Mycobacterium leprae, an obligate intracellular parasite. A problem in studying the transmission of leprosy is the small amount of variation in bacterial genomic DNA. The discovery of variable number of tandem repeats (VNTRs) allowed the detection of strain variation in areas with a high prevalence of leprosy. Four genotypes of M. leprae based on three single-nucleotide polymorphism (SNPs) were also discovered to be useful for analysis of the global spread of leprosy.
Methods: In this present study, we examined the allelic diversity of M. leprae at 16 select VNTR and three SNP loci using 89 clinical isolates obtained from patients mainly from the neighbouring states of São Paulo and Rio de Janeiro Brazil.
Results and conclusion: By use of a PCR-RFLP-based procedure that allows the recognition of SNP types 3 and 4 without the need for the more expensive DNA sequencing steps, characterisation of the main M. leprae genotypes was easy. When applied on the study population, it was found that the SNP type 3 is most frequent in these two states of Brazil, and that VNTRs provided further discrimination of the isolates. Two Short Tandem Repeats (STRs) were monomorphic, with the remaining 14 STRs represented by two to 18 alleles. Epidemiological associations with township or state were not evident in this random collection and require further investigations. In phylogenetic trees, branches formed by all 16 STRs clearly separated SNP type 3 organisms from the other types while the allelic patterns of two minisatellite loci 27-5 and 12-5 were highly correlated with SNP type 3. This strain typing study provide the basis for comparison of M. leprae strain types within Brazil and with those from other countries, and informed selection of genomic markers and methods for future studies.