Mechanisms of Heteroresistance to Isoniazid and Rifampin of M. tuberculosis in Tashkent, Uzbekistan

Heteroresistance of Mycobacterium tuberculosis is defined as the co-existence of organisms either susceptible or resistant to an anti-tuberculosis drug in one patient. Here, we analyzed the underlying mechanisms of heteroresistance to INH and RMP in 35 tuberculosis (TB) patients from Tashkent, Uzbekistan, using the Genotype MTBDR assay. The MTBDR assay is designed to detect wild-type and mutations of the 81-bp hotspot region of the rpoB gene and of codon 315 of the katG gene conferring resistance to rifampin (RMP) and isoniazid (INH), respectively. In seven of the 35 cases (20%), wild-type and resistant organisms were simultaneously detected, indicating heteroresistance. Using MIRU-VNTR analysis and IS6110 fingerprinting showed that in five of the seven cases, heteroresistance was caused by two different strains. In two cases, heteroresistance was due to infection with a single M. tuberculosis strain of the Beijing genotype split into organisms with and without resistance to a drug. These latter cases showed a history of relapse/treatment failure suggesting that poor treatment quality might have triggered the evolution of heteroresistance. For the first time, two different mechanisms of heteroresistance have been proven in one study set, the existence of two different strains suggesting super-infection, and the split of a MTB strain into resistant and susceptible lineages in the context of relapse or treatment failure and of an infection with Beijing genotype strains. Particularly, the detection of the latter mechanism might serve as quality marker for treatment progams in the future. The implications of these findings for clinical infection control practitioners as well as for pneumologists involved in TB control programs will be discussed in detail.