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Hypercyst Mutants in Rhodospirillum centenum Identify Regulatory Loci Involved in Cyst Cell Differentiation. James E. Berleman, 2004.Rhodospirillum centenum is a purple photosynthetic bacterium that forms resting cyst cells when starved for nutrients . In this study, we demonstrate that chalcone synthase gene (chsA) expression is developmentally regulated, with expression of chsA increasing up to 86-fold upon induction of the cyst developmental cycle . Screening for mini-Tn5-induced mutants that exhibit elevated chsA::lacZ expression has led to the isolation of a set of R . centenum mutants that display increased chsA gene expression concomitant with constitutive induction of the cyst developmental cycle . These "hypercyst" mutants have lost the ability to regulate cyst cell formation in response to nutrient availability . Sequence analysis indicates that the mini-Tn5-disrupted genes code for a variety of factors, including metabolic enzymes and a large set of potential regulatory factors, including four gene products with homology to histidine sensor kinases and three with homology to response regulators . Several of the disrupted genes also have sequence similarity to che-like signal transduction components . Rapid Direct Detection of Multiple Rifampin and Isoniazid Resistance Mutations in Mycobacterium tuberculosis in Respiratory Samples by Real-Time PCR. Mercedes Marín, 2004.Rapid detection of resistance in Mycobacterium tuberculosis can optimize the efficacy of antituberculous therapy and control the transmission of resistant M . tuberculosis strains . Real-time PCR has minimized the time required to obtain the susceptibility pattern of M . tuberculosis strains, but little effort has been made to adapt this rapid technique to the direct detection of resistance from clinical samples . In this study, we adapted and evaluated a real-time PCR design for direct detection of resistance mutations in clinical respiratory samples . The real-time PCR was evaluated with (i) 11 clinical respiratory samples harboring bacilli resistant to isoniazid (INH) and/or rifampin (RIF), (ii) 10 culture-negative sputa spiked with a set of strains encoding 14 different resistance mutations in 10 independent codons, and (iii) 16 sputa harboring susceptible strains . The results obtained with this real-time PCR design completely agreed with DNA sequencing data . In all sputa harboring resistant M . tuberculosis strains, the mutation encoding resistance was successfully detected . No mutation was detected in any of the susceptible sputa . The test was applied only to smear-positive specimens and succeeded in detecting a bacterial load equivalent to 103 CFU/ml in sputum samples (10 acid-fast bacilli/line) . The analytical specificity of this method was proved with a set of 14 different non-M . tuberculosis bacteria . This real-time PCR design is an adequate method for the specific and rapid detection of RIF and INH resistance in smear-positive clinical respiratory samples .
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