Variable numbers of TTC repeats in Mycobacterium leprae DNA from leprosy patients and use in strain differentiation

Strain differentiation of Mycobacterium leprae would be of great value for epidemiological investigation to identify the infectious sources of leprosy, to understand transmission patterns, and to distinguish between relapse and reinfection. From the M. leprae genome sequence database, TTC DNA repeats were identified. Primer sets designed to amplify the region flanking TTC repeats revealed PCR products of different sizes, indicating that the number of repeats at each locus may be variable among M. leprae strains. The TTC repeats were not found in Mycobacterium tuberculosis, Mycobacterium avium, Mycobacterium marinum, or human tissues, which indicated their specificity to M. leprae. Sequence analysis of the TTC repeat region in each of the M. leprae strains showed a variation of 10 to 37 repeats. In the M. leprae strains of 34 multibacillary patients at Cebu, Philippines, M. leprae with 24 and 25 TTC repeats was most common, and this was followed by strains with 14, 15, 20, 21, and 28 repeats. This study thus indicates that there are variable numbers of TTC repeats in a noncoding region of M. leprae strains and that the TTC region may be useful for strain differentiation for epidemiological investigations of leprosy.