Pyrazinamide (PZA) plays a crucial role in first-line tuberculosis drug therapy. Unlike other antimicrobial agents, PZA is active against Mycobacterium tuberculosis only at low pH. The basis for this conditional drug susceptibility remains undefined. In this study, we utilized a genome-wide approach to interrogate potentiation of PZA action. We found that mutations in numerous genes involved in central metabolism as well as cell envelope maintenance and stress response are associated with PZA resistance. Further, we demonstrate that constitutive activation of the cell envelope stress response can drive PZA susceptibility independent of environmental pH. Consequently, exposure to peptidoglycan synthesis inhibitors, such as beta-lactams and d-cycloserine, potentiate PZA action through triggering this response. These findings illuminate a regulatory mechanism for conditional PZA susceptibility and reveal new avenues for enhancing potency of this important drug through targeting activation of the cell envelope stress response.
Proton nuclear magnetic resonance (1H-NMR) is a widely used tool for chemical structural analysis. However, 1H-NMR spectra suffer from natural aberrations that render computer-assisted automated identification of these spectra difficult, and at times impossible. Previous efforts have successfully implemented instrument dependent or conditional identification of these spectra. In this paper, we report the first instrument independent computer-assisted automated identification system for a group of complex carbohydrates known as the xyloglucan oligosaccharides. The developed system is also implemented on the world wide web (http://www.ccrc.uga.edu) as part of an identification package called the CCRC-Net and is intended to recognize any submitted 1H-NMR spectrum of these structures with reasonable signal-to-noise ratio, recorded on any 500 MHz NMR instrument. The system uses Artificial Neural Networks (ANNs) technology and is insensitive to the instrument and environment-dependent variations in 1H-NMR spectroscopy. In this paper, comparative results of the ANN engine versus a multidimensional Bayes' classifier is also presented.
Abstract The genetic basis of virulence in Mycobacterium tuberculosis has been investigated through genome comparisons of its virulent (H37Rv) and attenuated (H37Ra) sister strains. Such analysis, however, relies heavily on the accuracy of the sequences. While the H37Rv reference genome has had several corrections to date, that of H37Ra is unmodified since its original publication. Here, we report the assembly and finishing of the H37Ra genome from single-molecule, real-time (SMRT) sequencing. Our assembly reveals that the number of H37Ra-specific variants is less than half of what the Sanger-based H37Ra reference sequence indicates, undermining and, in some cases, invalidating the conclusions of several studies. PE_PPE family genes, which are intractable to commonly-used sequencing platforms because of their repetitive and GC-rich nature, are overrepresented in the set of genes in which all reported H37Ra-specific variants are contradicted. We discuss how our results change the picture of virulence attenuation and the power of SMRT sequencing for producing high-quality reference genomes.
The PNS module is discussed as the building block for the synthesis of parallel, self-organizing, hierarchical, neural networks (PSHNN). The P- and NS-units are fractile in nature, meaning that each such unit may itself consist of a number of parallel PNS modules. Through a mechanism of statistical acceptance or rejection of input vectors for classification, the sample space is divided into a number of subspaces. The input vectors belonging to each subspace are classified by a dedicated set of PNS modules. This strategy results in considerably higher accuracy of classification and better generalization as compared to previous neural network models.< >
Abstract Point mutations in the rrs gene and eis promoter are known to confer resistance to second-line injectable drugs (SLIDs) amikacin (AMK), capreomycin (CAP), and kanamycin (KAN). While mutations in these canonical genes confer a majority of SLID-resistance, alternative mechanisms of resistance are not uncommon and threaten effective treatment decisions when using conventional molecular diagnostics. In total, 1184 clinical M. tuberculosis isolates from 7 countries were studied for genomic markers associated with phenotypic resistance. The markers rrs: A1401G and rrs: G1484T were associated with resistance to all three SLIDs, and three known markers in the eis promoter ( eis :G-10A, eis :C-12T, and eis :C-14T) were similarly associated with kanamycin resistance (KAN-R). Among 325, 324, 270 AMK-R, CAP-R, and KAN-R isolates, 264 (81.2%), 250 (77.2%), and 249 (92.3%) harbored canonical mutations, respectively. Thirteen isolates harbored more than one canonical mutation. Canonical mutations did not account for 111 of the phenotypically resistant isolates. A gene-wise method identified three genes and promoters with mutations that, on aggregate, associated with unexplained resistance to at least one SLID. Our analysis associated whiB7 promoter mutations with KAN resistance, supporting clinical relevance for the previously demonstrated role of whiB7 overexpression in KAN resistance. We also provide evidence for the novel association of ppe51 (a gene previously associated with various antimicrobial compounds) with AMK resistance, and for the novel association of thrB with AMK and CAP resistance. The use of gene-wise association can provide additional insight, and therefore is recommended for identification of rare mechanisms of resistance when individual mutations carry insufficient statistical power.
Abstract Background Rifampicin (RIF) is a key first-line drug used to treat tuberculosis, a pulmonary disease caused by Mycobacterium tuberculosis . However antibiotic resistance to RIF is prevalent despite an apparent fitness cost. RIF resistance is primarily caused by mutations in the RIF resistance determining region in the rpoB gene, at the cost of slower growth in rich media. Compensatory mutations in the genes rpoA and rpoC have been shown to alleviate this fitness cost. These compensatory mutations may explain how RIF resistant strains have spread so rapidly. However, the effect of compensation on transmission is still unclear, partly because of uncertainty over which rpoABC mutations compensate for which RIF resistance markers. Objectives We performed an association study on a globally representative set of 4309 whole genome sequenced clinical M. tuberculosis isolates to identify novel putative compensatory mutations, determine the prevalence of known and previously reported putative compensatory mutations, and determine which RIF resistance markers associate with these compensatory mutations. Results and Conclusions Only 20.0% (216/1079) of RIF resistant isolates carried previously reported high-probability compensatory mutations, suggesting existence of other compensatory mutations. Using a strict phylogenetic approach, we identified 18 novel putative compensatory mutations in rpoC, rpoB , and rpoA . Novel and previously reported compensatory mutations were strongly associated with the RIF R marker rpoB :S450L, suggesting compensation may be specific to particular RIF R markers. These findings will aid identification of RIF-resistant M. tuberculosis strains with restored fitness. Such strains pose a greater risk of causing resistant outbreaks.
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