engleski

Drug resistance analysis of Mycobacterium tuberculosis by means of drug susceptibility test and reverse hybridization-based line probe assay

Tuberculosis (TB) is the leading infectious cause of death worldwide. Croatia takes place among the countries with still high incidence of tuberculosis (33/100, 000 in 2002). Several countries around the world have registered outbreaks of mono- and even multidrug resistance (MDR) TB. Croatia has a low incidence of both (3% and 0.6%, respectively). MDR is defined as resistance to at least rifampin (one of the major first line anti-TB drug) and isoniazid, with or without resistance to other drugs. As to rifampin associated genetic modification in M. tuberculosis strain, this is the initial and precursory event of MDR. The objective of this study was to compare the classical drug susceptibility test (DST – proportion method on Loewenstein-Jensen medium) and the reverse hybridization-based line probe assay (INNO-LiPA Rif.TB, Innogenetics). The DST enables the differentiation for established resistance to rifampin, isoniazid, ethambutol and streptomycin, while INNO-LiPA Rif.TB enables the recognition of early genetic mutation of rifampin resistance region of the beta-subunit of the RNA polymerase (rpoB). Herein, we examined 39 M. tuberculosis strains of which 1 sensitive and 2 resistant only to rifampin, both by DST and INNO-LiPA Rif.TB. Among 20 rifampin and other anti-TB drugs resistant (MDR) strains by DST, INNO-LiPA Rif.TB allowed the identification of 19 strains resistant to rifampin, of which one was identified as mixture of the mutant strain (R4a) and the wild type (WT), while the remaining one was identified as only WT. Fourteen out of 16 samples resistant to anti-TB drugs other than rifampin were confirmed by INNO-LiPA Rif.TB, while 2 were identified as resistant to rifampin. The overall concordance of the two tests represents 92.3%. DST is very informative assay on TB drug resistance but it is time consuming and the interpretation of the results could be ambiguous contrary to INNO-LiPA Rif.TB. Beside that, INNO-LiPA Rif.TB assay is very reliable and simple to perform. Moreover, it allows the identification of genetic mutation before the appearance of phenotypic changes of the bacteria. Thus, it could be considered as the screening test for drug resistance for M. tuberculosis strains.

Drug resistance; Mycobacterium tuberculosis; drug susceptibility test; reverse hybridization-based line probe assay

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