|
|
|
|
|
|
Genes of Bacillus cereus and Bacillus anthracis Encoding Proteins of the Exosporium. Sarah J. Todd, 2003.The exosporium is the outermost layer of spores of Bacillus cereus and its close relatives Bacillus anthracis and Bacillus thuringiensis . For these pathogens, it represents the surface layer that makes initial contact with the host . To date, only the BclA glycoprotein has been described as a component of the exosporium; this paper defines 10 more tightly associated proteins from the exosporium of B . cereus ATCC 10876, identified by N-terminal sequencing of proteins from purified, washed exosporium . Likely coding sequences were identified from the incomplete genome sequence of B . anthracis or B . cereus ATCC 14579, and the precise corresponding sequence from B . cereus ATCC 10876 was defined by PCR and sequencing . Eight genes encode likely structural components (exsB, exsC, exsD, exsE, exsF, exsG, exsJ, and cotE) . Several proteins of the exosporium are related to morphogenetic and outer spore coat proteins of B . subtilis, but most do not have homologues in B . subtilis . ExsE is processed from a larger precursor, and the CotE homologue appears to have been C-terminally truncated . ExsJ contains a domain of GXX collagen-like repeats, like the BclA exosporium protein of B . anthracis . Although most of the exosporium genes are scattered on the genome, bclA and exsF are clustered in a region flanking the rhamnose biosynthesis operon; rhamnose is part of the sugar moiety of spore glycoproteins . Two enzymes, alanine racemase and nucleoside hydrolase, are tightly adsorbed to the exosporium layer; they could metabolize small molecule germinants and may reduce the sensitivity of spores to these, limiting premature germination . Effects of Amoxicillin Subinhibitory Concentrations on the Cross-Protection Developed by Pneumococcal Antibodies in Mouse Sepsis Caused by an Amoxicillin-Resistant Serotype 6B Streptococcus pneumoniae Strain. D. Tarragó, 2004.A model of mouse sepsis caused by a serotype 6B Streptococcus pneumoniae strain (amoxicillin MIC of 8 µg/ml) was developed to investigate the therapeutic effect of an amoxicillin dose (3.12 mg/kg of body weight three times daily for 48 h) producing, over the whole treatment period, subinhibitory concentrations in serum (peak concentration [Cmax]: 6.1 µg/ml) in animals that prior to infection had been passively immunized with a 6B or 23F hyperimmune serum (obtained by immunization with a whole-cell heat-inactivated inoculum and diluted to produce no protective effect by itself) . Mortality in nonimmunized animals treated with antibiotic (3.12 mg/kg) was 90%, and mortality in animals immunized but not treated with the antibiotic was 100% . Antibiotic treatment in immunized animals produced mortality rates  20% when the hyperimmune serum was used, thus showing cross-protection and synergism (defined as the situation in which there is no response to the single agents [no differences versus placebo] while the combination exhibits significant activity) with subinhibitory concentrations of the antibiotic . The presence of antipneumococcal antibodies allowed antibiotic efficacy with negligible values of pharmacodynamic parameters (Cmax/MIC ratio of <1 and thus a null value for the time that serum levels exceed the MIC) . This in vivo synergism offers a potential therapeutic strategy against resistant strains .
T2182C Mutation in 23S rRNA Is Associated with Clarithromycin Resistance in Helicobacter pylori Isolates Obtained in Bangladesh. Rasel Khan, 2004.Twelve clarithromycin-resistant (MIC,  1 µg/ml) Helicobacter pylori isolates were analyzed for point mutations in the 23S rRNA gene . Sequence analysis of all of the resistant isolates revealed a T-to-C transition mutation at position 2182 . Transformation experiments confirmed that a single T-to-C transition mutation at position 2182 is associated with clarithromycin resistance .
Recombinant Environmental Libraries Provide Access to Microbial Diversity for Drug Discovery from Natural Products. Sophie Courtois, 2003.To further explore possible avenues for accessing microbial biodiversity for drug discovery from natural products, we constructed and screened a 5,000-clone "shotgun" environmental DNA library by using an Escherichia coli-Streptomyces lividans shuttle cosmid vector and DNA inserts from microbes derived directly (without cultivation) from soil . The library was analyzed by several means to assess diversity, genetic content, and expression of heterologous genes in both expression hosts . We found that the phylogenetic content of the DNA library was extremely diverse, representing mostly microorganisms that have not been described previously . The library was screened by PCR for sequences similar to parts of type I polyketide synthase genes and tested for the expression of new molecules by screening of live colonies and cell extracts . The results revealed new polyketide synthase genes in at least eight clones . In addition, at least five additional clones were confirmed by high-pressure liquid chromatography analysis and/or biological activity to produce heterologous molecules . These data reinforce the idea that exploiting previously unknown or uncultivated microorganisms for the discovery of novel natural products has potential value and, most importantly, suggest a strategy for developing this technology into a realistic and effective drug discovery tool .
|
© 2005
Transgalactic Ltd (manufacturer of Bioscreen C software) |
Privacy Statement | P.O. Box
1393, 00101 Helsinki, Finland,
Last modified: May 25, 2005
| ||||||
