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Transcriptional Profiling of Caulobacter crescentus during Growth on Complex and Minimal Media. Alison K. Hottes, 2004.Microarray analysis was used to examine gene expression in the freshwater oligotrophic bacterium Caulobacter crescentus during growth on three standard laboratory media, including peptone-yeast extract medium [PYE] and minimal salts medium with glucose or xylose as the carbon source . Nearly 400 genes [approximately10% of the genome] varied significantly in expression betweenat least two of these media . The differentially expressed genesincluded many encoding transport systems, most notably diverseTonB-dependent outer membrane channels of unknown substratespecificity . Amino acid degradation pathways constituted thelargest class of genes induced in PYE . In contrast, many ofthe genes upregulated in minimal media encoded enzymes for synthesisof amino acids, including incorporation of ammonia and sulfateinto glutamate and cysteine . Glucose availability induced expressionof genes encoding enzymes of the Entner-Doudoroff pathway, whichwas demonstrated here through mutational analysis to be essentialin C . crescentus for growth on glucose . Xylose induced expressionof genes encoding several hydrolytic exoenzymes as well as anoperon that may encode a novel pathway for xylose catabolism.A conserved DNA motif upstream of many xylose-induced geneswas identified and shown to confer xylose-specific expression.Xylose is an abundant component of xylan in plant cell walls,and the microarray data suggest that in addition to servingas a carbon source for growth of C . crescentus, this pentosemay be interpreted as a signal to produce enzymes associatedwith plant polymer degradation. Synergy of Daptomycin with Oxacillin and Other ß-Lactams against Methicillin-Resistant Staphylococcus aureus. Kenneth H. Rand, 2004.We previously observed marked synergy between daptomycin and both rifampin and ampicillin against vancomycin-resistant enterococci (VRE) . Because the synergy between daptomycin and ampicillin was observed for 100% of VRE strains with high-level ampicillin resistance (ampicillin MIC of  128 µg/ml), we looked for synergy between daptomycin and other ß-lactams against 18 strains of methicillin-resistant Staphylococcus aureus (MRSA) by employing a time-kill method using Mueller-Hinton broth supplemented to 50 mg of Ca2+/liter . All strains were resistant to oxacillin (16 of 18 strains were resistant at drug concentrations of
256 µg/ml), and all strains were susceptible to daptomycin (the MIC at which 90% of the tested isolates were inhibited was 1 µg/ml) . Daptomycin was tested at concentrations of 2, 1, 0.5, 0.25, 0.125, and 0.0625 µg/ml alone or in combination with oxacillin at a fixed concentration of 32 µg/ml . Synergy was found for all 18 strains with daptomycin at one-half the MIC in combination with 32 µg of oxacillin/ml, and synergy was found for 11 of 18 strains (61%) with daptomycin at one-fourth the MIC or less in combination with oxacillin . At 24 h, the daptomycin-oxacillin combination with daptomycin at one-half the MIC showed bactericidal activity against all 18 strains, and the combination with one-fourth the daptomycin MIC showed bactericidal activity against 9 of 18 strains . We also used a novel screening method to look for synergy between daptomycin and other ß-lactams . In this approach, daptomycin was incorporated into Ca2+-supplemented Mueller-Hinton agar at subinhibitory concentrations, and synergy was screened by comparing test antibiotic Kirby-Bauer disks on agar with and without daptomycin . By this method, daptomycin with ampicillin-sulbactam, ticarcillin-clavulanate, or piperacillin-tazobactam showed synergy comparable to or greater than daptomycin with oxacillin . For seven of the eight strains tested, time-kill studies confirmed synergy between daptomycin and ampicillin-sulbactam with ampicillin in the range of 2 to 8 µg/ml . The combination of daptomycin and ß-lactams may be useful for the treatment of MRSA infection, but further studies are needed to elucidate the mechanisms and to determine the in vivo efficacy of the combination .
Prophage Contribution to Bacterial Population Dynamics. Lionello Bossi, 2003.Cocultures of Salmonella strains carrying or lacking specific prophages undergo swift composition changes as a result of phage-mediated killing of sensitive bacteria and lysogenic conversion of survivors . Thus, spontaneous prophage induction in a few lysogenic cells enhances the competitive fitness of the lysogen population as a whole, setting a selection regime that forces maintenance and spread of viral DNA . This is likely to account for the profusion of prophage sequences in bacterial genomes and may contribute to the evolutionary success of certain phylogenetic lineages . Virus Succession Observed during an Emiliania huxleyi Bloom. Declan C. Schroeder, 2003.Denaturing gradient gel electrophoresis was used as a molecular tool to determine the diversity and to monitor population dynamics of viruses that infect the globally important coccolithophorid Emiliania huxleyi . We exploited variations in the major capsid protein gene from E . huxleyi-specific viruses to monitor their genetic diversity during an E . huxleyi bloom in a mesocosm experiment off western Norway . We reveal that, despite the presence of several virus genotypes at the start of an E . huxleyi bloom, only a few virus genotypes eventually go on to kill the bloom . Waterborne Outbreak of Gastroenteritis Associated with a Norovirus. Sandhya U. Parshionikar, 2003.The Wyoming Department of Health investigated an outbreak of acute gastroenteritis among persons who dined at a tourist saloon in central Wyoming during October 2001 . Human caliciviruses (HuCVs) were suspected as the etiological agent of the outbreak based on the incubation period, duration of illness, and symptoms observed in ill patrons . A retrospective cohort study demonstrated that ill patrons were 4.5 times more likely to have exposure to drinking water and/or ice than nonill patrons . No food items were associated with illness . An environmental investigation gave evidence that the saloon's groundwater was contaminated with sewage . Water from the saloon's only well was processed for viruses . The processed water sample and stool samples collected from three ill patrons were analyzed by reverse transcription-PCR (RT-PCR) for the presence of HuCV . All positive RT-PCR results were confirmed by sequence and phylogenetic analyses of cloned RT-PCR products . A genogroup I, subtype 3, HuCV stain was found to be present in the well water sample and two stool samples . In addition, a genogroup II, subtype 6, strain was detected in one stool sample . The identification of the same HuCV strain in both the well water and stool samples strongly suggests a link between exposure to well water and the outbreak of gastroenteritis . The presence of a genogroup II, subtype 6, strain in one of the stool samples suggests that multiple HuCV strains may have been involved in this outbreak . The laboratory isolation of HuCV strains from outbreak-associated drinking water is relatively novel in the United States . This investigation outlines the procedure for virus isolation and illustrates the utility of RT-PCR for the identification of HuCV in large volumes of water and stool samples obtained during outbreaks of acute nonbacterial gastroenteritis .
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