Evaluation of the effectiveness of molecular genetic and bacteriological methods in determining heteroresistance Mycobacterium tuberculosis to rifampicin

Abstract

We analyzed bacterial suspensions (mixtures) containing various proportions of resistant and susceptible strains to assess the effectiveness of molecular genetic tests and bacteriological methods for determination of the heteroresistant population of M. tuberculosis (MTB) to rifampicin (RIF). We established that the efficiency of determining the RIF-resistant MTB population in mixtures depends on the method of mutation detection used in the test system. The Genotype MTBDRplus, TB-TEST, and TB-BIOCHIP-1 tests showed the same results in detecting a resistant population with the Ser531Leu mutation. Genotype MTBDRplus more effectively detected His526Tyr, His526Asp, Asp516Val substitutions and less efficiently detected mutations determined by the absence of wild-type probes compared to TB-TEST and TB-BIOCHIP-1 tests.The efficiency of bacteriological detection of the resistant MTB population depends on the terms of cultivation. The method of serial microdilutions in the Middlebrook 7H9 liquid medium is the most effective in detecting RIF-resistance in the heteroresistant MTB population with the MTB cultivation for 21 days in comparison with the automated system Bactec MGIT 960 and the method of absolute concentrations on the L-J solid medium with the MTB cultivation for 28 days. It was noted that the proportion of resistant MTB strains detectection by Bactec MGIT 960, the method of absolute concentrations on a solid L-J medium for 28 days and by the method of serial microdilutions for 14 days did not differ significantly and amounted to 45.1; 44.1 and 38.9 respectively