Rapid identification of Mycobacterium tuberculosis Beijing genotypes on the basis of the mycobacterial interspersed repetitive unit locus 26 signature.

Mycobacterium tuberculosis Beijing strains are prevalent in many parts of the world and often give rise to large institutional outbreaks. Such highly transmissible strains, often associated with multidrug resistance, are likely underrepresented in outbreaks reported from developing countries, mainly due to nonavailability of fast detection methods suitable in epidemiological surveillance studies. We evaluated a PCR assay based on amplification of mycobacterial interspersed repetitive unit locus 26 as a stand-alone method for unambiguous identification of Beijing strains. The method was used on blinded samples from 10 standard strains whose Beijing status was already confirmed by spoligotyping. All 10 strains were accurately identified, and their profiles were corroborated successfully with spoligotypes. The method was also applied to 70 different non-Beijing clinical isolates from different countries to allow discrimination of isolates. Owing to its accuracy, simplicity, and rapidity, the assay can be employed in laboratory-level testing of isolates linked to certain outbreaks. The test can also be adopted for direct application on clinical samples to save time on culturing bacilli for genotyping.