IDENTIFICATION OF A NEW DNA REGION-SPECIFIC FOR MEMBERS OF MYCOBACTERIUM-TUBERCULOSIS COMPLEX

The successful use of DNA amplification for the detection of tuberculo us mycobacteria crucially depends on the choice of the target sequence , which ideally should be present in all tuberculous mycobacteria and absent from all other bacteria. In the present study we developed a PC R procedure based on the intergenic region (IR) separating two genes e ncoding a recently identified mycobacterial two-component system named SenX3-RegX3. The senX3-regX3 IR is composed of a novel type of repeti tive sequence, called mycobacterial interspersed repetitive units (MIR Us). In a survey of 116 Mycobacterium tuberculosis strains characteriz ed by different IS6110 restriction fragment length polymorphisms, 2 My cobacterium africanum strains, 3 Mycobacterium bovis strains (includin g 2 BCG strains), and 1 Mycobacterium microti strain, a specific PCR f ragment was amplified in all cases. This collection included M. tuberc ulosis strains that lack IS6110 or mtp40, two target sequences that ha ve previously been used for the detection of M. tuberculosis. No PCR f ragment was amplified when DNA froth other organisms was used, giving a sensitivity of 100% and a specificity of 100% in the confidence limi t of this study. The numbers of MIRUs were found to vary among strains , resulting in six different groups of strains on the basis of the siz e of the amplified PCR fragment. However, the vast majority of the str ains (approximately 90%) fell within the same group, containing two 77 -bp MIRUs followed by one 53-bp MIRU.