|
|
|
|
|
|
Nosocomial Spread of Ceftazidime-Resistant Klebsiella pneumoniae Strains Producing a Novel Class A ß-Lactamase, GES-3, in a Neonatal Intensive Care Unit in Japan. Jun-ichi Wachino, 2004.Klebsiella pneumoniae strain KG525, which showed high-level resistance to broad-spectrum cephalosporins, was isolated from the neonatal intensive care unit (NICU) of a Japanese hospital in March 2002 . The ceftazidime resistance of strain KG525 was transferable to Escherichia coli CSH-2 by conjugation . Cloning and sequence analysis revealed that production of a novel extended-spectrum class A ß-lactamase (pI 7.0), designated GES-3, which had two amino acid substitutions of M62T and E104K on the basis of the sequence of GES-1, was responsible for resistance in strain KG525 and its transconjugant . The blaGES-3 gene was located as the first gene cassette in a class 1 integron that also contained an aacA1-orfG fused gene cassette and one unique cassette that has not been described in other class 1 integrons and ended with a truncated 3' conserved segment by insertion of IS26 . Another five ceftazidime-resistant K . pneumoniae strains, strains KG914, KG1116, KG545, KG502, and KG827, which were isolated from different neonates during a 1-year period in the same NICU where strain KG525 had been isolated, were also positive for GES-type ß-lactamase genes by PCR . Pulsed-field gel electrophoresis and enterobacterial repetitive intergenic consensus-PCR analyses displayed genetic relatedness among the six K . pneumoniae strains . Southern hybridization analysis with a GES-type ß-lactamase gene-specific probe showed that the locations of blaGES were multiple and diverse among the six strains . These findings suggest that within the NICU setting genetically related K . pneumoniae strains carrying the blaGES gene were ambushed with genetic rearrangements that caused the multiplication and translocation of the blaGES gene . Regulation of Fumonisin Biosynthesis in Fusarium verticillioides by a Zinc Binuclear Cluster-Type Gene, ZFR1. Joseph E. Flaherty, 2004.Fusarium verticillioides, a pathogen of maize, produces a class of mycotoxins called fumonisins in infected kernels . In this study, a candidate regulatory gene, ZFR1, was identified in an expressed sequence tag library enriched for transcripts expressed by F . verticillioides during fumonisin B1 (FB1) biosynthesis . ZFR1 deletion mutants exhibited normal growth and development on maize kernels, but fumonisin production was reduced to less than 10% of that of the wild-type strain . ZFR1 encodes a putative protein of 705 amino acids with sequence similarity to the Zn(II)2Cys6 binuclear cluster family that are regulators of both primary and secondary metabolism in fungi . Expression of ZFR1 in colonized germ and degermed kernel tissues correlated with FB1 levels . Overexpression of ZFR1 in zfr1 mutants restored FB1 production to wild-type levels; however, FB1 was not restored in an fcc1 (Fusarium C-type cyclin) mutant by overexpression of ZFR1 . The results of this study indicate that ZFR1 is a positive regulator of FB1 biosynthesis in F . verticillioides and suggest that FCC1 is required for ZFR1 function . Lactococcal Plasmid pNP40 Encodes a Novel, Temperature-Sensitive Restriction-Modification System. Jonathan O'Driscoll, 2004.A novel restriction-modification system, designated LlaJI, was identified on pNP40, a naturally occurring 65-kb plasmid from Lactococcus lactis . The system comprises four adjacent similarly oriented genes that are predicted to encode two m5C methylases and two restriction endonucleases . The LlaJI system, when cloned into a low-copy-number vector, was shown to confer resistance against representatives of the three most common lactococcal phage species . This phage resistance phenotype was found to be strongly temperature dependent, being most effective at 19°C . A functional analysis confirmed that the predicted methylase-encoding genes, llaJIM1 and llaJIM2, were both required to mediate complete methylation, while the assumed restriction enzymes, specified by llaJIR1 and llaJIR2, were both necessary for the complete restriction phenotype . A Northern blot analysis revealed that the four LlaJI genes are part of a 6-kb operon and that the relative abundance of the LlaJI-specific mRNA in the cells does not appear to contribute to the observed temperature-sensitive profile . This was substantiated by use of a LlaJI promoter-lacZ fusion, which further revealed that the LlaJI operon appears to be subject to transcriptional regulation by an as yet unidentified element(s) encoded by pNP40 . The Global Regulatory hns Gene Negatively Affects Adhesion to Solid Surfaces by Anaerobically Grown Escherichia coli by Modulating Expression of Flagellar Genes and Lipopolysaccharide Production. Paolo Landini, 2002.The initial binding of bacterial cells to a solid surface is a critical and essential step in biofilm formation . In this report we show that stationary-phase cultures of Escherichia coli W3100 (a K-12 strain) can efficiently attach to sand columns when they are grown in Luria broth medium at 28°C in fully aerobic conditions . In contrast, growth in oxygen-limited conditions results in a sharp decrease in adhesion to hydrophilic substrates . We show that the production of lipopolysaccharide (LPS) and of flagella, as well as the transcription of the fliC gene, encoding the major flagellar subunit, increases under oxygen-limited conditions . Inactivation of the global regulatory hns gene counteracts increased production of LPS and flagella in response to anoxia and allows E . coli W3100 to attach to sand columns even when it is grown under oxygen-limited conditions . We propose that increased production of the FliC protein and of LPS in response to oxygen limitation results in the loss of the ability of E . coli W3100 to adhere to hydrophilic surfaces . Indeed, overexpression of the fliC gene results in a decreased adhesion to sand even when W3100 is grown in fully aerobic conditions . Our observations strongly suggest that anoxia is a negative environmental signal for adhesion in E . coli . Glutathione and Catalase Provide Overlapping Defenses for Protection against Respiration-Generated Hydrogen Peroxide in Haemophilus influenzae. Bjorn Vergauwen, 2003.Glutathione is an abundant and ubiquitous low-molecular-weight thiol that may play a role in many cellular processes, including protection against the deleterious effects of reactive oxygen species . We address here the role of glutathione in protection against hydrogen peroxide (H2O2) in Haemophilus influenzae and show that glutathione and catalase provide overlapping defense systems . H . influenzae is naturally glutathione deficient and imports glutathione from the growth medium . Mutant H . influenzae lacking catalase and cultured in glutathione-deficient minimal medium is completely devoid of H2O2 scavenging activity and, accordingly, substantial amounts of H2O2 accumulate in the growth medium . H . influenzae generates H2O2 at rates similar to those reported for Escherichia coli, but the toxicity of this harmful metabolite is averted by glutathione-based H2O2 removal, which appears to be the primary system for protection against H2O2 endogenously generated during aerobic respiration . When H2O2 concentrations exceed low micromolar levels, the hktE gene-encoded catalase becomes the predominant scavenger . The requirement for glutathione in protection against oxidative stress is analogous to that in higher and lower eukaryotes but is unlike the situation in other bacteria in which glutathione is dispensable for aerobic growth during both normal and oxidative stress conditions . Complement Resistance Is Essential for Colonization of the Digestive Tract of Hirudo medicinalis by Aeromonas Strains. Thomas R. Braschler, 2003.From the crop of the medicinal leech, Hirudo medicinalis, only Aeromonas veronii bv . sobria can be cultured consistently . Serum-sensitive A . veronii mutants were unable to colonize H . medicinalis, indicating the importance of the mammalian complement system for this unusual simplicity . Complementation of one selected mutant restored its ability to colonize . Serum-sensitive mutants are the first mutant class with a colonization defect for this symbiosis .
|
© 2005
Transgalactic Ltd (manufacturer of Bioscreen C software) |
Privacy Statement | P.O. Box
1393, 00101 Helsinki, Finland,
Last modified: May 25, 2005
| ||||||
