Objective: To evaluate the reliability and feasibility of two methods of multilocus variable number of tandem repeat analysis (MLVA) for strain typing of M. leprae, and to study whether short tandem repeat loci are stable and suitable for epidemiological study of leprosy.
Methods: Total DNA was extracted from skin biopsies of 20 new multibacillary (MB) patients from China diagnosed in 2006. To determine the copy numbers of short tandem repeats (STRs) for 13 loci, we amplified each locus individually by PCR, followed by sequence analysis of the amplicons. Separately, the same loci, plus four others were amplified by Multiplex PCRs (MP) using fluorescent primers and the copy number was identified by fragment length analysis (MP-FLA). MLVA was also performed at different times during treatment for a subset of the patients.
Results and conclusions: Genetic variability of M. leprae in China can be assessed in microsatellite loci. (GTA)9 and (TTC)21 loci are hypervariable, with array sizes of 25 repeat units or more. The expansion of the (GTA)9 locus is a characteristic of some M. leprae isolates in China. A high level of allele concordance was observed between PCR-sequencing and MP-FLA methods. However, MP-FLA method was cost-effective, rapid, high throughput and suitable for strain typing. Five of the 20 isolates of M. leprae were from patients residing in the same township in Qiubei County, Yunnan, and matched closely by MLVA. Three of these patients are family contacts of previously diagnosed patients, with intra-familial strain types being similar, suggesting infections from common sources and transmission chain(s). The VNTR patterns were highly similar in biopsy and slit skin smears (SSS) before treatment, and in the SSS collected at various time points during treatment. Taken together, VNTR strain typing is a useful tool for study of short range transmission in leprosy.