Clinical and bacteriological characteristics associated with clustering of multidrug-resistant tuberculosis.

SETTING: The impact of the genetic characteristics of Mycobacterium tuberculosis on the clustering of multidrug-resistant tuberculosis (MDR-TB) has not been analyzed together with clinical and demographic characteristics. OBJECTIVE: To determine factors associated with genotypic clustering of MDR-TB in a community-based study. DESIGN: We measured the proportion of clustered cases among MDR-TB patients and determined the impact of clinical and demographic characteristics and that of three M. tuberculosis genetic characteristics: lineage, drug resistance-associated mutations, and rpoA and rpoC compensatory mutations. RESULTS: Of 174 patients from California and Texas included in the study, the number infected by East-Asian, Euro-American, Indo-Oceanic and East-African-Indian M. tuberculosis lineages were respectively 70 (40.2%), 69 (39.7%), 33 (19.0%) and 2 (1.1%). The most common mutations associated with isoniazid and rifampin resistance were respectively katG S315T and rpoB S531L. Potential compensatory mutations in rpoA and rpoC were found in 35 isolates (20.1%). Hispanic ethnicity (OR 26.50, 95%CI 3.73-386.80), infection with an East-Asian M. tuberculosis lineage (OR 30.00, 95%CI 4.20-462.40) and rpoB mutation S531L (OR 4.03, 95%CI 1.05-23.10) were independent factors associated with genotypic clustering. CONCLUSION: Among the bacterial factors studied, East-Asian lineage and rpoB S531L mutation were independently associated with genotypic clustering, suggesting that bacterial factors have an impact on the ability of M. tuberculosis to cause secondary cases.

Predicting differential rifamycin resistance in clinical Mycobacterium tuberculosis isolates by specific rpoB mutations.

SETTING: Rifampin (RMP) resistant Mycobacterium tuberculosis is usually assumed to be resistant to all rifamycins. Increasing evidence indicates, however, that some rpoB mutations, detectable by rapid molecular diagnostics, confer resistance to RMP but not to rifabutin (RBT), suggesting that RBT may be effective for the treatment of M. tuberculosis with these mutations. OBJECTIVE: To determine if specific rpoB mutations reliably predict differential phenotypic resistance to RMP and RBT. DESIGN: We selected 60 clinical M. tuberculosis isolates from a repository of multinational multidrug-resistant tuberculosis isolates and stratified them into two groups: 1) those with rpoB mutations suspected to confer differential resistance to RMP and RBT, and 2) those expected to be cross-resistant to RMP and RBT. These assumptions were tested by comparing the phenotypic susceptibilities of RMP/RBT with those predicted by mutations in the rpoB gene. RESULTS: Of 20 suspected RMP-resistant/RBT-susceptible isolates, 15 were RMP-resistant but RBT-susceptible, 3 were RMP- and RBT-susceptible, and 2 were cross-resistant to both RMP and RBT. In comparison, 40 of 40 suspected cross-resistant isolates were both RMP- and RBT-resistant. CONCLUSION: Our data support the association between specific rpoB mutations and differential resistance of M. tuberculosis to RMP and RBT. Clinical studies are required to investigate the efficacy of RBT in the treatment of M. tuberculosis harboring these mutations.

Phenotypic and genotypic diversity in a multinational sample of drug-resistant Mycobacterium tuberculosis isolates.

OBJECTIVE: To develop and evaluate rapid, molecular-based drug susceptibility testing (DST) for extensively drug-resistant tuberculosis (XDR-TB), we assembled a phenotypically and genotypically diverse collection of Mycobacterium tuberculosis isolates from patients evaluated for drug resistance in four high-burden countries. METHODS: M. tuberculosis isolates from India (n = 111), Moldova (n = 90), the Philippines (n = 96), and South Africa (n = 103) were selected from existing regional and national repositories to maximize phenotypic diversity for resistance to isoniazid, rifampin (RMP), moxifloxacin, ofloxacin, amikacin, kanamycin, and capreomycin. MGIT™ 960 was performed on viable isolates in one laboratory using standardized procedures and drug concentrations. Genetic diversity within drug resistance phenotypes was assessed. RESULTS: Nineteen distinct phenotypes were observed among 400 isolates with complete DST results. Diversity was greatest in the Philippines (14 phenotypes), and least in South Africa (9 phenotypes). Nearly all phenotypes included multiple genotypes. All sites provided isolates resistant to injectables but susceptible to fluoroquinolones. Many patients were taking drugs to which their disease was resistant. DISCUSSION: Diverse phenotypes for XDR-TB-defining drugs, including resistance to fluoroquinolones and/or injectable drugs in RMP-susceptible isolates, indicate that RMP susceptibility does not ensure effectiveness of a standard four-drug regimen. Rapid, low-cost DST assays for first- and second-line drugs are thus needed.

First documentation of isoniazid reversion in Mycobacterium tuberculosis.

BACKGROUND: Drug-resistant strains of Mycobacterium tuberculosis are increasing worldwide and pose a major threat to global health. However, it remains unsettled whether drug-resistant mutants are fixed in the bacterial population or if they would revert in the absence of drug pressure. OBJECTIVE: To document the occurrence of isoniazid (INH) reversion in a patient with multidrug-resistant tuberculosis (TB) and investigate its association with fitness cost. DESIGN: Genotypic and phenotypic assays were used to characterize the reversion of INH resistance in isolates from a patient with pulmonary TB. The pre-reversion katG mutation was reconstructed in a pan-susceptible laboratory strain (H37Rv DeltakatG::katG W300G) and tested for susceptibility to INH and oxidative stress. RESULTS: Genotyping and drug susceptibility testing showed that an isogenic strain of M. tuberculosis reverted from an INH-resistant to a susceptible phenotype in the absence of INH therapy. The genotypic basis of this reversion was mapped to the katG codon 300 which reverted from GGG (glycine, G) to a wild-type codon, TGG (tryptophan, W). The H37Rv DeltakatG::katG W300G mutant was resistant to INH, but also showed a deficiency in coping with oxidative stress. CONCLUSION: This study confirms that, in the absence of INH pressure, some INH-resistant mutants will revert to a drug-susceptible phenotype. This finding may have broader implications for INH-resistant strains and for the clinically useful lifespan of INH.