A customized dual-locus VNTR combination for genotyping Burkholderia mallei field isolates in Iran

Burkholderia mallei, the causative agent of Glanders, is a host-adapted bacterium that does not survive outside of its mostly soliped hosts. Iran is among those countries that experience annual outbreaks of the disease. Recently, multiple locus variable number of tandem repeat analysis (MLVA) has achieved broad acceptance as the method of choice in genotyping of B. mallei. In order to comparative assessment of diversity indices provided by two tandem repeat loci namely VNTR1217 and VNTR13, five Iranian B. mallei strains were examined by VNTR-PCR. The amplification products were sequenced to guaranty accuracy of sizing and nucleotide structure of unit repeats. A further 29 B. mallei strains were also included in the study. As observed, all the 34 B. mallei strains carried the VNTR13 locus that was characterized by this study while VNTR1217 was missing in the genome of 4 studied strains. A higher Nei's diversity index (Nei' di=0.80) was presented by VNTR13 compared to that of VNTR1217 (Nei's di= 0.74) when MLVA applied on the whole panel of 34 strains. Among the Iranian strains, VNTR13 detected 3 alleles while VNTR1217 found two alleles. Findings of this study back the assumption that if a standard panel of VNTR loci are to be selected for a universal MLVA typing system suitable for B. mallei, all the reported loci from across the world are then expected to assess against a global collection of B. mallei strains. Such extensive investigation is possible only if an international collaboration between OIE-approved Glanders reference laboratories is set.