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Necessity of Meningococcal  -Glutamyl
Aminopeptidase for Neisseria meningitidis Growth in Rat Cerebrospinal
Fluid (CSF) and CSF-Like Medium.Hideyuki Takahashi, 2004.The growth of a -glutamyl
aminopeptidase (GGT)-deficient Neisseria meningitidis strain
was much slower than that of the parent strain in rat cerebrospinal
fluid (CSF) and in a synthetic CSF-mimicking medium, and the growth
failure was suppressed by the addition of cysteine . These results
suggested that, in the environment of cysteine shortage,
meningococcal GGT provided an advantage for meningococcal
multiplication by supplying cysteine from environmental
-glutamyl-cysteinyl
peptides .
Inhibitor-Sensitive AmpC ß-Lactamase Variant Produced by an Escherichia coli Clinical Isolate Resistant to Oxyiminocephalosporins and Cephamycins. Yohei Doi, 2004.Escherichia coli HKY28, a ceftazidime-resistant strain isolated from a urine specimen in Japan, produced an inhibitor-sensitive AmpC ß-lactamase variant . The deduced amino acid sequence of the enzyme contained a number of substitutions and a tripeptide deletion (Gly286-Ser287-Asp288) compared with the sequence of native AmpC of E . coli . When the deletion was reverted by a 9-base insertion at the relevant site of ampC in the clone, the typical inhibitor-resistant phenotype of AmpC was restored, while at the same time the levels of resistance to ceftazidime, cefpirome, and cefepime were reduced eightfold or more . Molecular modeling studies indicated that a structural change took place in the H-10 helix as a result of the deletion, and this change caused an alteration of the substrate binding site, leading to a unique phenotype analogous to that of inhibitor-sensitive class A extended-spectrum ß-lactamases . The degree of inhibition was greater with sulbactam and tazobactam than with clavulanic acid . To our knowledge, this is the first report to have characterized an E . coli ampC that encodes chromosomal AmpC ß-lactamase sensitive to the available ß-lactamase inhibitors . Construction and Characterization of Transposon Insertion Mutations in Corynebacterium diphtheriae That Affect Expression of the Diphtheria Toxin Repressor (DtxR). Diana Marra Oram, 2002.Transcription of the bacteriophage-borne diphtheria toxin gene tox is negatively regulated, in response to intracellular Fe2+ concentration, by the chromosomally encoded diphtheria toxin repressor (DtxR) . Due to a scarcity of tools, genetic analysis of Corynebacterium diphtheriae has primarily relied on analysis of chemically induced and spontaneously occurring mutants and on the results of experiments with C . diphtheriae genes cloned in Escherichia coli or analyzed in vitro . We modified a Tn5-based mutagenesis technique for use with C . diphtheriae, and we used it to construct the first transposon insertion libraries in the chromosome of this gram-positive pathogen . We isolated two insertions that affected expression of DtxR, one 121 bp upstream of dtxR and the other within an essential region of the dtxR coding sequence, indicating for the first time that dtxR is a dispensable gene in C . diphtheriae . Both mutant strains secrete diphtheria toxin when grown in medium containing sufficient iron to repress secretion of diphtheria toxin by wild-type C . diphtheriae . The upstream insertion mutant still produces DtxR in decreased amounts and regulates siderophore secretion in response to iron in a manner similar to its wild-type parent . The mutant containing the transposon insertion within dtxR does not produce DtxR and overproduces siderophore in the presence of iron . Differences in the ability of the two mutant strains to survive oxidative stress also indicated that the upstream insertion retained slight DtxR activity, whereas the insertion within dtxR abolished DtxR activity . This is the first evidence that DtxR plays a role in protecting the cell from oxidative stress .
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