Molecular Typing of Mycobacterium tuberculosis Based on Variable Number of Tandem DNA Repeats Used Alone and in Association with Spoligotyping

Fingerprinting based on variable numbers of tandem DNA repeats (VNTR), a recently described methodology, was evaluated for molecular typing of Mycobacterium tuberculosis in an insular setting. In this study, VNTR fingerprinting was used alone or as a second-line test in association with spoligotyping, double-repetitive-element PCR (DRE-PCR), and IS6110 restriction fragment length polymorphism (RFLP) analysis, and the discriminatory power for each method or the combination of methods was compared by calculating the Hunter-Gaston discriminative index (HGI). The results obtained showed that in 6 out of 12 (50%) cases, VNTR-defined clusters were further subdivided by spoligotyping, compared to 7 out of 18 (39%) cases where spoligotyping-defined clusters were further subdivided by VNTR. When used alone, VNTR was the least discriminatory method (HGI = 0.863). Although VNTR was significantly more discriminatory when used in association with spoligotyping (HGI = 0.982), the combination of spoligotyping and DRE-PCR (HGI = 0.992) was still the most efficient among rapid, PCR-based methodologies, giving results comparable to IS6110 RFLP analysis. Nonetheless, VNTR typing may provide additional phylogenetical information that may be helpful to trace the molecular evolution of tubercle bacilli.