Project description:The identification of multidrug resistant (MDR), extensively and totally drug resistant Mycobacterium tuberculosis (Mtb), in vulnerable sites such as Mumbai, is a grave threat to the control of tuberculosis. The current study aimed at explaining the rapid expression of MDR in Directly Observed Treatment Short Course (DOTS) compliant patients, represents the first study comparing global transcriptional profiles of 3 pairs of clinical Mtb isolates, collected longitudinally at initiation and completion of DOTS. While the isolates were drug susceptible (DS) at onset and MDR at completion of DOTS, they exhibited identical DNA fingerprints at both points of collection. The whole genome transcriptional analysis was performed using total RNA from H37Rv and 3 locally predominant spoligotypes viz. MANU1, CAS and Beijing, hybridized on MTBv3 (BuG@S) microarray, and yielded 36, 98 and 45 differentially expressed genes respectively. Genes encoding transcription factors (sig, rpoB), cell wall biosynthesis (emb genes), protein synthesis (rpl) and additional central metabolic pathways (ppdK, pknH, pfkB) were found to be down regulated in the MDR isolates as compared to the DS isolate of the same genotype. Up regulation of drug efflux pumps, ABC transporters, trans-membrane proteins and stress response transcriptional factors (whiB) in the MDR isolates was observed. The data indicated that Mtb, without specific mutations in drug target genes may persist in the host due to additional mechanisms like drug efflux pumps and lowered rate of metabolism. Furthermore this population of Mtb, which also showed reduced DNA repair activity, would result in selection and stabilization of spontaneous mutations in drug target genes, causing selection of a MDR strain in the presence of drug pressures. Efflux pump such as drrA may play a significant role in increasing fitness of low level drug resistant cells and assist in survival of Mtb till acquisition of drug resistant mutations with least fitness cost. [Data is also available from http://bugs.sgul.ac.uk/E-BUGS-134]
Project description:Bacterial persister cells are phenotypic variants of regular cells that are tolerant to antibiotics. Analysis of clinical isolates of M. tuberculosis showed that strains vary substantially in their tolerance to antibiotics. The level of persisters was very high is some isolates, suggesting that these are hip mutants. We investigated gene expression differences in eight clinical isolates, four of which we characterized as high-persister strains and four as low-persister, or regular, strains. Comparison of gene expression patterns may provide clues as to the genetic mechanisms underlying persister formation.
Project description:While several groups, including our own, have examined variability of M. tuberculosis at the DNA level, this is the first systematic survey of variability in mRNA expression among clinical isolates of M. tuberculosis. Genes whose expression varies among isolates when assayed under a single growth condition may make poor drug targets and vaccine antigens and may affect molecular diagnostics, so they can be used to narrow down lists of candidate molecules. Because the measurement of gene expression is extremely sensitive to environmental conditions, comparison of gene expression is labour intensive. In this study, we surveyed 12 strains. These strains are a subset of those for which we have already published genomic deletion information (Kato-Maeda et al., 2001). In order to ensure maximum reproducibility of the experiments and avoid complications caused by differences in growth conditions, we measured gene expression under well-controlled in vitro conditions. Our aims were to provide an overview of gene expression variability among clinical isolates under a single growth condition and to test whether gene functional classes are related to variability in expression. Set of arrays that are part of repeated experiments Keywords: Biological Replicate