Evaluation of the discriminatory power of variable number tandem repeat (VNTR) typing of Mycobacterium bovis strains

Abstract

The discriminatory power of variable number tandem repeat (VNTR) typing based on 16 known loci (12 MIRUs, 3 ETRs and VNTR 3232) was assessed for Mycobacterium bovis strains collected sequentially at the slaughterhouse of N'Djaména, Chad. Of 67 M. bovis strains analyzed, 67% were clustered. In this study, VNTR typing was highly discriminative with an overall allelic diversity (h(oa)) of 0.922. We defined five loci (ETR A, B, C and MIRU 26, 27) as highly (h>0.25), two loci (MIRU 4, and VNTR 3232) as moderately (0.11<h<0.25) and three loci (MIRU 16, 20, 31) as poorly (0.01<h<0.11) discriminative. Six loci (MIRU 2, 10, 23, 24, 39, and 40) showed no polymorphism at all. VNTR typing of the five highly discriminative loci (h=0.917) proved to be most appropriate for first line typing of M. bovis strains of Chad and superior than spoligotyping (h(sp)=0.789). In contrast to Mycobacterium tuberculosis strains, a consensus on VNTR loci needs to be found for M. bovis strains. The selection of a generally agreed set of VNTR loci for molecular discrimination of M. bovis in different geographical settings is discussed.