SPECIFIC DIFFERENTIATION BETWEEN MYCOBACTERIUM-BOVIS BCG AND VIRULENT-STRAINS OF THE MYCOBACTERIUM-TUBERCULOSIS COMPLEX

A PCR procedure based on the intergenic region (IR) separating two gen es encoding a recently identified mycobacterial two-component system, named SenX3-RegX3, was developed and was shown to be suitable for iden tifying Mycobacterium bovis BCG. The senX3-regX3 IR contains a novel t ype of repetitive sequence, called mycobacterial interspersed repetiti ve units (MIRUs). All tested BCG strains exclusively contained 77-bp M IRUs within the senX3-regX3 IR, whereas all non-BCG M. tuberculosis co mplex strains contained a 53-bp MIRU, in addition to the 77-bp MIRUs. All 148 strains analyzed so far could be divided into eight different groups according to the copy numbers of the 77-bp MIRU and to the pres ence or absence of the 53-bp MIRU. BCG strains contained either one, t wo, or three 77-bp MIRUs, The other strains contained one to five 77-b p MIRUs invariably followed by a 53-bp MIRU. The consistent absence of the 53-bp MIRU in BCG strains and its presence in virulent strains al lowed us to develop an enzyme-linked immunosorbent assay using specifi c capture oligonucleotide probes to distinguish between BCG and other M. tuberculosis complex strains.