Identification of a Haarlem Genotype-Specific Single Nucleotide Polymorphism in the mgtC Virulence Gene of Mycobacterium tuberculosis

MgtC is a virulence factor common to several intracellular pathogens, includingMycobacterium tuberculosis , that might have been acquired through horizontal gene transfer. In the present study, we investigated the polymorphism ofmgtC in clinical isolates representative of the main epidemic groups ofM. tuberculosis . MgtC appears to have a low polymorphism rate inM. tuberculosis that consists exclusively of nonsynonymous mutations. We identified a single nucleotide polymorphism (SNP) atmgtC codon 182 (mgtC 182 ) specifically associated with the Haarlem genotype. A simple PCR assay, called the “on/off switch assay,” using phosphorothioate-modified primers andPfu polymerase allowed us to distinguish Haarlem from non-Haarlem strains based on themgtC 182 SNP. The amino acid change (H182R) associated with themgtC 182 SNP in Haarlem strains does not appear to procure a selective advantage. Our results offer a simple and rapid tool to distinguish between Haarlem and non-Haarlem strains. In addition, the on/off switch assay, which allows the detection of SNPs on chromosomal DNA andM. tuberculosis cultures, provides a novel approach for the screening of known SNPs inM. tuberculosis .