The global threat posed by drug-resistant strains of Mycobacterium tuberculosis demands a greater understanding of the genetic basis and molecular mechanisms that govern how such strains develop resistance against various antituberculous drugs. In this report, we examine a new genetic basis for resistance to one of the oldest and most widely used second-line drugs employed in tuberculosis therapy, streptomycin (SM). This marker for SM resistance was first discovered on the basis of genomic data obtained from drug-resistant M. tuberculosis strains collected in Japan, wherein an association was observed between SM resistance and a mutation in gidB, a putative 16S rRNA methyltransferase. By evaluating an isogenic ⌬gidB mutant strain constructed from strain H37Rv, we demonstrate the causal role of gidB in conferring a low-level SM-resistant phenotype in M. tuberculosis with a 16-fold increase in the MIC over the parent strain. Among clinical isolates, the modest increase in SM resistance conferred by a gidB mutation leads to an MIC distribution of gidB mutation-containing strains that spans the recommended SM breakpoint concentration currently used in drug susceptibility testing protocols. As such, some gidB mutation-containing isolates are found to be SM sensitive, while others are SM resistant. On the basis of a pharmacodynamic analysis and Monte Carlo simulation, those isolates that are found to be SM sensitive should still respond favorably to SM treatment, while nearly half of those found to be SM resistant will likely respond poorly. This report provides the first microbiological evidence for the contribution of gidB in streptomycin resistance and examines the clinical implications of mutations in the gidB gene.The World Health Organization (WHO) 2010 report estimates that 440,000 cases of multidrug-resistant (MDR) tuberculosis (TB) emerged in 2008, with 5.4% of these cases being extensively drug resistant (XDR) TB (36). The strains responsible for producing these forms of TB incur far greater mortality and morbidity to TB patients than drug-sensitive strains (12, 13). If left undetected, these drug-resistant strains can further propagate throughout a community with the potential to cause an epidemic of untreatable, drug-resistant TB. Yet if the patients receive a proper diagnosis and are properly cared for, the success of treatment of MDR-TB can be as high as 60% (36). Therefore, there is an urgent need for faster, more accurate diagnostic alternatives to the current, culture-based drug susceptibility test (DST) methods, which require at least 6 to 9 weeks to determine the resistance pattern of the organism. Fortunately, molecular-based diagnostic methods have already begun to emerge as a viable alternative (2, 23, 38). The most successful of these are based on detecting genotypic polymorphisms associated with drug resistance. In order for these improved methods to supplant culture-based methods, the molecular mechanisms and genetic bases that underlie drug resistance must be understood.In many parts of the w...

Background: We have previously reported that TNF-α levels correlate to total mycobacterial burden in tuberculosis (TB) patients. Objective: To characterize the dynamics of cytokine responses in TB patients during chemotherapy to identify potential surrogate markers for effective treatment. Methods: Following induction by culture filtrate proteins in whole blood, production patterns of TNF-α, IL-10, IFN-γ and IL-12 were measured in 23 non-multidrug-resistant (MDR)-TB and 16 MDR-TB patients and in 31 healthy controls. Rates of mycobacterial clearance from the sputum were then measured and compared. Results: Prior to the initiation of chemotherapy, TNF-α and IL-10 levels were significantly higher in TB patients than in healthy controls while IFN-γ and IL-12 levels were similar. During chemotherapy, the levels of all 4 cytokines increased. We evaluated these responses separately in patients that did and did not clear their sputum culture at 2 and 6 months. At 2 months, decreases in both IFN-γ and IL-12 correlated strongly with a successful early response, while after 6 months of therapy, when half (7/14) of MDR-TB patients were still sputum culture positive, downregulation of TNF-α was uniquely correlated with sputum conversion between the groups. Conclusion: Our findings suggest the possibility that the regulation of TNF-α production in whole blood may be a more specific indicator of sputum conversion at 6 months than IFN-γ, IL-12 or IL-10 in MDR-TB patients.

pncA mutation in M. tuberculosis is a major mechanism of PZA resistance in MDR isolates from patients in South Korea. The patterns of mutation might be more scattered and diverse. DNA-based diagnosis of PZA resistance has potential for the rapid detection of drug resistance.

We evaluated the utility of the "QuantiFERON®-TB Gold in tube" (QuantiFERON®) test that uses TB-specific antigens for the diagnosis of latent infection in such individuals. We also examined the correlation between the IFN-γ response to these antigens and the exposure risk to TB by evaluating antigen-specific IFN-γ release in comparison with IFN-γ release in response to PPD in three groups; medical students, nurses in a TB hospital, and TB patients. All nurses and TB patients responded to PPD whereas 79.2 % (p=0.04) and 52 % (p<0.0001) responded to QuantiFERON®, respectively. In the medical students, only 10.4 % responded to QuantiFERON® while 85.2 % were positive to PPD (p < 0.0001). There was also a significant correlation between the levels of IFN-γ production and the duration of employment in the group of nurses at the TB hospital suggesting on-going exposure in this high risk group. Thus these results demonstrate that Mycobacterium tuberculosis-specific IFN-γ release assay accurately discriminates low and high risk healthy subjects and might therefore be a useful diagnostic tool for the diagnosis of latent infection in BCG-vaccinated individuals.