Evaluation of variable number tandem repeat (VNTR) loci in molecular typing of Mycobacterium bovis isolates from Ireland

Various sets of short tandem repeats such as the exact tandem repeats (ETRs), mycobacterial interspersed repetitive units (MIRUs) and variable number tandem repeat (VNTR) loci, have recently been described as effective tools in strain typing M. tuberculosis complex isolates, representative of global diversity. This study extends our previous study, evaluating the discrimination of a further 17 MIRU_VNTR loci individually and comparing the resolution of published VNTR sets and spoligotyping using a panel of 47 local M. bovis field isolates, including known epidemiologically linked isolates and 9 M. tuberculosis complex reference isolates. Individual loci differed greatly in their discrimination. The discriminatory capacity of novel combinations of the most discriminating VNTR loci was also assessed. In the panel of 47 M. bovis isolates, 17 unique profiles were resolved using VNTR set 1, whilst the MIRUs and ETRs resolved the panel into 11 and 6 profiles, respectively. A novel combination of 10 highly discriminatory VNTRs was determined, which resolved 30 unique profiles. The configuration of a multi-locus VNTR-based assay and its ability to provide a flexible, convenient and high-resolution genotyping method is discussed. We suggest a panel of VNTR markers which may be widely suitable for molecular epidemiological studies of M. bovis. However, the number and combination of informative VNTR markers selected needs to be determined empirically with reference to locally prevalent strains and will depend on the epidemiological study requirements.