The individual molecular mechanisms of resistance have been identified for all first-line drugs and the majority of second-line drugs [7]. In M. tuberculosis, resistance to RMP results from mutations in the β-subunit of RNA polymerase, which is encoded by the rpoB gene [8]. Approximately 95% of RMP-resistant strains carry mutations within an 81-bp region containing codons

507 through 533 of the rpoB gene [8–10]. The single mechanism of resistance and narrow distribution of mutations make rpoB-81 bp region very attractive for Elacridar molecular detection of resistance to RMP [11, 12]. However, within several dozen different mutations detected in the rpoB-81 bp region of RMP-resistant M. tuberculosis strains [for review see [13]], very few were tested by cloning and complementation assays. Mutated rpoB genes (S531L; H526Y; D516V) were introduced into the RMP sensitive M. tuberculosis H37Rv strain, resulting 3-deazaneplanocin A in vitro in acquired drug resistance of the host strain [14]. These authors observed that the level of acquired resistance was higher for mutants carrying mutations in codons 531 and 526 compared to mutation in codon 516. In this paper a genetic model was constructed allowing for a relatively simple verification of the relationship between the presence of a given mutation in rpoB-81 bp region and the RMP resistance of the host

strain carrying such a mutation. Some rpoB mutations revealed drug-resistance only in selected M. tuberculosis strains suggesting that genetic background of the host is important for the development of resistance to RMP. Methods Bacterial strains and growth conditions The M. tuberculosis strains examined for this study were isolated from TB patients in Poland in 2000 during the second national survey of drug resistance [12, 15]. Eight clinical strains identified as drug resistant, carrying different mutations in the

rpoB gene, and two susceptible strains identified as drug sensitive, which did not carry any mutation in rpoB, were selected. Moreover, a control laboratory strain M. tuberculosis H37Ra, was included in this study. Primary isolation, differentiation, and drug susceptibility testing were performed with Cobimetinib chemical structure AZD5153 Lowenstein-Jensen (LJ) medium and the BACTEC 460-TB system (Becton-Dickinson, Sparks, Md.), as reported earlier [15]. All mycobacterial strains used in this study were cultured in Middlebrook 7H9 broth supplemented with OADC (albumin-dextrose-sodium chloride) and with kanamycin (25 μg/ml), or hygromycin (10 μg/ml), when required. Mycobacterial transformants were selected on Middlebrook 7H10 agar plates enriched with OADC containing kanamycin (Km) or hygromycin (Hyg). Gene cloning strategies Standard molecular biology protocols were used for all cloning procedures [16].