Bacteriological and Molecular Analysis of Rifampin-Resistant Mycobacterium tuberculosis Strains Isolated in Australia

Abstract

To develop a better understanding of the epidemiology and molecular biology of rifampin-resistant Mycobacterium tuberculosisstrains in Australia, 50 clinical isolates (33 rifampin-resistant and 17 rifampin-sensitive strains) cultured between 1990 and 1997 were analyzed by a number of bacteriological and molecular techniques. Examination of the drug resistance profiles of the 33 rifampin-resistant isolates revealed that 91% were resistant to rifampin in combination with resistance to isoniazid, 88% were resistant to rifampin on first isolation, and 81% showed cross-resistance with rifabutin. On the basis of the demographic data provided for the patients infected with the rifampin-resistant strains, 90% of the patients were born overseas. Of these patients, 64% developed clinical symptoms within 5 years of residence in Australia. On a molecular level, analysis of the rpoB gene revealed that 97% of the rifampin-resistant isolates had missense mutations within a conserved region of the gene, and eight types of missense mutations were detected. Of the 31 rifampin-resistant isolates that were typed by restriction fragment length polymorphism (RFLP) analysis, 28 distinct patterns were obtained by RFLP analysis with IS6110, and three clusters of genetically related isolates were identified. All isolates within the clusters were from patients who were born overseas and who had the same country of origin. The results from this study provide an overview of the current situation of rifampin resistance in Australia and can serve as a basis for continued monitoring of drug-resistant M. tuberculosis strains isolated within the country.

Association of specific mutations in katG, rpoB, rpsL and rrs genes with spoligotypes of multidrug-resistant Mycobacterium tuberculosis isolates in Russia

“…The frequencies of mutations in rpoB codons 516 (5.4%), 526 (15%) and 531 (71%) of the Beijing family isolates are similar to those reported for isolates in the north-west region of Russia [13] and the Archangel region [17]. The mutation 531TTG in rpoB is the most commonly observed mutation in rifampicin-resistant isolates in many parts of the world, e.g., in Brazil (54%) [24], the USA (35%) [25], India (38.7%) [26], Germany (65%) [27] and Australia (52%) [28]. The predominance of mutations in rpoB codon 531 of the rifampicin-resistant isolates belonging to the Beijing family is in good agreement with frequencies of mutations in codons of the rpoB gene and rates of growth of spontaneous rifampicin-resistant mutants of M. tuberculosis strain H37Rv [29], and Mycobacterium leprae, Mycobacterium africanum and Mycobacterium avium strains [30].…”

In-vitro activity of rifabutin against rifampicin-resistant Mycobacterium tuberculosis isolates with known rpoB mutations

“…Although different susceptibility testing methods have been used, and some discrepancies have been reported, such studies have generally revealed a strong correlation between certain rpoB mutations and the MICs of rifampicin and rifabutin. According to these previous studies, all rifampicin-resistant isolates with Asp516Val or Asp516Tyr substitutions were susceptible to rifabutin, with the exception of two isolates reported by Yuen et al [14] with MICs of > 1 mg ⁄ L. In the present study, three isolates with Asp516Val or Asp516Tyr substitutions were also found to be rifabutin-susceptible. Rifampicinresistant isolates with His526Tyr, His526Asp, His526Arg or His526Pro substitutions and mutations at codons 513 and 531 were almost always resistant to rifabutin.…”

“…Rifampicinresistant isolates with His526Tyr, His526Asp, His526Arg or His526Pro substitutions and mutations at codons 513 and 531 were almost always resistant to rifabutin. However, two isolates with a Ser531Leu mutation were reported as rifabutinsusceptible by Yang et al [13] and Yuen et al [14]. In the present study, all isolates with the mutations mentioned above were resistant to rifabutin.…”

“…Although minor discrepancies have been reported [13,14], in general a correlation exists between the MICs of rifampicin and rifabutin. Isolates with In the present study, a clear correlation was also determined between high-level resistance to rifampicin and resistance to rifabutin.…”

Rapid detection of resistance in Mycobacterium tuberculosis: a review discussing molecular approaches

“…Nevertheless, DNA sequencing is the technique of choice according to several studies on the genotypic detection of resistant TB strains. It has been applied to isolates from a wide variety of geographic origins, in the search for mutations in multiple loci of: MDR strains [23], RIF-r in rpoB [8,9,[24][25][26], RIF-r outside the RRDR core [27], INH in ndh [28], and katG [29], and EMB-r [17,30,31].…”