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S Iyobe

Publications and source records attributed to S Iyobe.

At least 19 recordsLinked to original sources
PubMed2005

Prevalence of Streptococcus pneumoniae isolates bearing macrolide resistance genes in association with integrase genes of conjugative transposons in Japan.

The relationship between susceptibility to macrolides and tetracycline, and the distribution of the resistance genes erm(B), mef(A) and tet(M) and the integrase gene of the conjugative transposon, Int-Tn, was examined in 43 isolates of Streptococcus pneumoniae from Gunma Prefecture, Japan. Thirty-five isolates were resistant to both macrolides and tetracycline and carried tet(M); erm(B) and mef(A) were detected in 19 and 16, respectively, of these isolates. Sixteen mef(A)-positive isolates were all identified as mef(E) variants. Int-Tn of Tn1545 was associated with 17 erm(B)- and 14 mef(A)-bearing isolates, and Int-Tn of Tn5252 was found in the remaining two mef(A)-carrying isolates. Pneumococcal strains with resistance to macrolides conferred by erm(B) or mef(A) in association with the integrase gene of conjugative transposon Tn1545 or Tn5252 appear to be prevalent in Japan.

Bacterial Proteins↗
PubMed2001

[Metallo-beta-lactamase producing bacteria].

Metallo-beta-lactamases are the carbapenemases belonging to the class B beta-lactamases on a molecular level. Two types of the metallo-beta-lactamase, IMP-1 and VIM-1, which have been detected mainly from Pseudomonas aeruginosa, respectively, in Japan and in Europe are especially important, because of the broad substrate specificity. These enzymes confer resistance to not only the carbapenems but also almost all beta-lactam antibiotics expect for monobactams. Clinical strains producing IMP-1 type enzymes are easily detectable by the PCR method or by the double-disk method using the enzyme inhibitor of mercapto-compound and the substrate antibiotic such as imipenem or ceftazidime. The gene blaIMP is frequently identified as a cassette inserted in the integron structure on the transmissible plasmids, disseminating among various gram-negative bacteria.

Bacteria↗
PubMed2000

Amino acid substitutions in a variant of IMP-1 metallo-beta-lactamase.

In the course of surveying for the carbapenem-hydrolyzing metallo-beta-lactamase gene bla(IMP) in pathogenic bacteria by the PCR method, we detected a gene encoding a variant metallo-beta-lactamase, designated IMP-3, which differed from IMP-1 by having low hydrolyzing activity for penicillins and carbapenems. PCR product direct sequencing of a 2.2-kb segment revealed that the gene bla(IMP-3) was located on a cassette inserted within a class I integron in the pMS390 plasmid. The 741-bp nucleotide sequence of bla(IMP-3) was identical to that of bla(IMP-1), except for seven base substitutions. Among these were two, at nucleotide positions 314 and 640, which caused amino acid alterations. Hybrid bla genes were constructed from bla(IMP-3) and bla(IMP-1) by recombinant DNA techniques, and beta-lactamases encoded by these genes were compared with those of the parents IMP-3 and IMP-1 under the same experimental conditions. The kinetic parameters indicated that the inefficient hydrolysis of benzylpenicillin, ampicillin, imipenem, and ceftazidime by IMP-3 was due to the substitution of glycine for serine at amino acid residue 196 in the mature enzyme. This alteration corresponded to the presence of guanine instead of an adenine at nucleotide position 640 of the bla(IMP-3) gene. This indicated that extension of the substrate profile in the metallo-beta-lactamase IMP-1 compared to IMP-3 is the result of a one-step single-base mutation, suggesting that the gene bla(IMP-3) is an ancestor of bla(IMP-1).

Amino Acid Substitution↗
PubMed2000

Detection of carbapenemase-producing Acinetobacter baumannii in a hospital.

Acinetobacter baumannii strains resistant to both imipenem (IPM) and ceftazidime (CAZ) were isolated from 1994 through 1996 at Gunma University Hospital. Nine isolates from different inpatients were examined for carbapenem-hydrolyzing activity and for the carbapemase gene bla(IMP) by the PCR method. All nine isolates were carbapenemase-producing strains that hydrolyzed IPM and that harbored bla(IMP). The bla(IMP) gene was transmissible by conjugation to an IPM-susceptible recipient strain of A. baumannii and conferred resistance to IPM, CAZ, cefotaxime (CTX), ampicillin (AMP), and piperacillin (PIP). Either intermediate or high-level resistance to amikacin (AMK) was transferred from two and five strains, respectively, concomitantly with bla(IMP), and gentamicin (GEN) resistance was also transferred in one instance of high-level AMK resistance. Comparative examination of clinical isolates for resistance patterns to nine drugs, IPM, CAZ, CTX, aztreonam, AMP, PIP, AMK, GEN, and norfloxacin, in addition to pulsed-field gel electrophoresis patterns with NotI-digested genomic DNA, confirmed nosocomial transmission of infections involving carbapenemase-producing A. baumannii strains.

Acinetobacter↗
PubMed1999

Role of permeability in the activities of beta-lactams against gram-negative bacteria which produce a group 3 beta-lactamase.

The production of a group 3 beta-lactamase permitted Escherichia coli to raise the MICs of ceftazidime, cefpirome, and meropenem greatly but those of imipenem and piperacillin only slightly. The ratios of maximum rate of hydrolysis to K(m) of ceftazidime, cefpirome, and piperacillin were lower than those of meropenem and imipenem for the group 3 beta-lactamase. The permeability coefficients for piperacillin and meropenem were higher than those for ceftazidime and cefpirome. Imipenem had the highest permeability coefficient.

Anti-Bacterial Agents↗
PubMed1998

Novel metallo beta-lactamase mediated by a Shigella flexneri plasmid.

Novel carbapenem-hydrolyzing beta-lactamase (newly named MET-1) encoded on a transferable plasmid pMS390 from Shigella flexneri JS19622 was purified. The molecular weight was 28,000 by SDS-PAGE and the isoelectric point was higher than 9.3. This beta-lactamase favorably hydrolyzed classical cephalosporins and oxyimino-cephalosporins rather than penicillins and carbapenems, but did not hydrolyze monobactams. The enzymatic activity was inhibited by EDTA, and the enzyme was found to contain two moles of zinc per mole of enzyme protein by means of atomic absorption spectrophotometry. These results indicated that the enzyme is a zinc beta-lactamase which differs from known metallo beta-lactamases, especially in its cephalosporinase-type substrate profile.

Bacterial Proteins↗
PubMed1998

An effective method for isolating alginate lyase-producing Bacillus sp. ATB-1015 strain and purification and characterization of the lyase.

A new alginate lyase-producing micro-organism, designated as Bacillus sp. strain ATB-1015, was effectively isolated from soil samples pretreated for 3 months with a substrate of the enzyme, sodium alginate. Alginate lyase activity was assayed by the degrading activity of biofilm of Teflon sheet discs, which was formed by a mucoid strain of Pseudomonas aeruginosa PAM3 selected from clinical isolates. The extracellular alginate lyase was precipitated with ammonium sulphate from the culture broth, and purified by gel filtration and anion exchange chromatography. The molecular weight of the lyase was estimated to be 41 kDa by SDS polyacrylamide gel electrophoresis and Sephacryl S-200 HR column chromatography. The optimum pH and temperature for the enzyme activity were around 7.5 and 37 degrees C, respectively, and the Km value was 0.17% with the substrate, sodium alginate. The lyase activity was completely inhibited by treatment with 1 mmol l-1 of EDTA and the decreased activity was almost completely recovered by the addition of 2 mmol l-1 of CaCl2. The activity was not affected by treatment with the protein denaturants, 0.01 mol l-1 of SDS or 1 mmol l-1 of urea. The lyase had substrate specificity for both the poly-guluronate and poly-mannuronate units in the alginate molecule.

Alginates↗
PubMed1997

[Mechanism of acquiring drug-resistance genes in pathogenic bacteria].

Pathogenic bacteria acquire resistance to chemotherapeutic agents by mutational events in the intrinsic genes or by incorporating foreign resistance genes. The resistance genes to various drugs were transferred among bacteria by transformation with free DNA, phage-mediated transduction, or cell to cell conjugation. Plasmids are capable of self-replication and self-transfer by conjugation. Drug-resistance genes are incorporated into plasmids by transposable elements, transposons. Several kinds of transposons carrying resistance genes to various drugs, or some transposons carrying multiresistance genes, are mobile among genetic elements and confer multiresistance on pathogenic bacteria. There is a specific element, integron, on transposons or plasmids. The integron has the gene and the site for incorporating resistance genes as cassettes and allows expression of the genes.

Bacteria↗
PubMed1997

[Appearance of extended-spectrum beta-lactamases].

Extended-spectrum beta-lactamases (ESBLs) are enzymes which hydrolyze broad-spectrum beta-lactam antibiotics by expanding the substrate spectra into the so-called anti-beta-lactamase beta-lactams such as oxyimino-cephalosporins, cephamycins, oxacephems, carbapenems and monobactams, conferring resistance to many kinds of beta-lactams on pathogenic bacteria. Recently, ESBLs have been demonstrated from various types of beta-lactamases phylogenetically belonging to the molecular class, A, B, C, or D. The genes coding for ESBLs are chromosome- or plasmid-mediated and some of them have developed by point or insertion mutations in the parental genes coding for the narrow-spectrum beta-lactamase. If the genes are plasmid-mediated, the dissemination among various species of pathogenic bacteria would cause hospital-acquired infections by ESBL-producing bacteria.

Anti-Bacterial Agents↗
PubMed1996

Imipenem and cephem resistant Pseudomonas aeruginosa carrying plasmids coding for class B beta-lactamase.

From October 1988 to January 1992, nine isolates of Pseudomonas aeruginosa carrying transferable plasmids encoding imipenem-hydrolyzing beta-lactamase (pI = c. 9.5) were recovered from nine different patients in a neurosurgical ward of a hospital in Japan. The beta-lactamase activities of the sonicated extracts from the transconjugants were inhibited by EDTA and this was partially reversible by the addition of zinc cation. The substrate specificity and pI of the beta-lactamase were similar to those of the metallo beta-lactamases from P. aeruginosa and Serratia marcescens TN9106. All strains were resistant to imipenem, carbenicillin and antipseudomonal cephems including ceftazidime, cefsulodin, cefpirome, while four and five strains were susceptible to piperacillin and aztreonam, respectively. Both low level imipenem resistance and high level cephem resistance were co-transferred with the production of metallo beta-lactamase, while resistance to piperacillin, aztreonam, and high level imipenem-resistance were not selected. Production of chromosomal cephalosporinase in piperacillin resistant strains was derepressed, and production of outer membrane protein of D2 was diminished in highly imipenem resistant strains. Six strains were isolated in 1991, and the amounts of antipseudomonal agents, especially imipenem, used in the neurosurgical ward increased markedly in this year. Only three of the nine isolates had the same serotype, pyocin type and phage type. Our results suggest that the repeated isolation of imipenem and cephem-resistant P. aeruginosa producing metallo beta-lactamase was related to the high usage of antipseudomonal beta-lactam antibiotics such as imipenem, and was exacerbated by the dissemination of a plasmid.

Anti-Infective Agents↗
PubMed1995

In vitro antibacterial activity of DU-6859a, a new fluoroquinolone.

The in vitro antibacterial activity of DU-6859a, a new fluoroquinolone, against a wide variety of clinical isolates was evaluated and compared with those of tosufloxacin, ofloxacin, ciprofloxacin, and sparfloxacin. DU-6859a showed potent broad-spectrum activity against gram-positive, gram-negative, and anaerobic bacteria, and its activity was greater than those of the control quinolones. By comparison of MICs at which 90% of strains are inhibited, DU-6859a had potent activity against bacteria resistant to the control quinolones. The time-killing curves of quinolones showed that the number of viable cells decreased rapidly during 2 to 4 of incubation, and regrowth was not seen even after 8 h incubation. At a concentration of four times the MIC, the frequencies of appearance of spontaneous mutants of Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa resistant to DU-6859a were < or = 4.0 x 10(-9) to 1.9 x 10(-8). The 50% inhibitory concentrations of DU-6859a were 0.86 and 1.05 micrograms/ml for the supercoiling activities of DNA gyrases isolated from E. coli and P. aeruginosa, respectively. The rank order of the 50% inhibitory concentrations observed for both DNA gyrases roughly paralleled the MICs.

Anti-Infective Agents↗
PubMed1995

nfxC-type quinolone resistance in a clinical isolate of Pseudomonas aeruginosa.

Quinolone resistance gene nqr-T91 in a clinical isolate of Pseudomonas aeruginosa P1481 was cotransducible with catA1 in P. aeruginosa PAO. The nqr-T91 transductant, PKH-T91, was resistant to norfloxacin, imipenem, and chloramphenicol and showed less norfloxacin accumulation than the parent strain did. Loss of the 46-kDa outer membrane protein (D2) and an increase in the 50-kDa outer membrane protein in PKH-T91 were observed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Lipopolysaccharides in the transductant were also changed. These alterations were considered to be related to lower levels of norfloxacin accumulation in PKH-T91. These genetic and biochemical properties suggested that an nfxC type of quinolone-resistant mutation occurred in a clinical isolate of P. aeruginosa P1481.

4-Quinolones↗
PubMed1995

[Postantibiotic effects (PAE's) of macrolide antibiotics evaluated using Bioscreen C method].

Postantibiotic effects (PAE's) of macrolide antibiotics were determined for Staphylococcus aureus and Enterococcus faecalis using viable counting and Bioscreen C method and the two methods were compared. No major differences between the two methods were observed. The Bioscreen C method was less laborious than the viable counting. The durations of PAE for S. aureus following exposures to erythromycin (EM), josamycin (JM) and rokitamycin (RKM) for 2 hours at twice the MICs were in ranges of 0.85 to 1.45, 2.36 to 3.48 and 1.93 to 5.45 hours, respectively. A definite PAE of 1.0 to 5.8 hours was also observed in E. faecalis strains exposed for 2 hours to EM, JM and RKM at twice the MICs.

Anti-Bacterial Agents↗
PubMed1994

Cloning and expression in Enterobacteriaceae of the extended-spectrum beta-lactamase gene from a Pseudomonas aeruginosa plasmid.

An extended-spectrum beta-lactamase, the gene for which is located on plasmid pMS350 in Pseudomonas aeruginosa strains, hydrolyzes carbapenems and other extended-spectrum beta-lactam antibiotics. We cloned the pMS350 beta-lactamase gene in an Escherichia coli K-12 strain using the vector plasmid pHSG398, and subcloned it into pMS360, a plasmid with a wide host-range. This resulted in the formation of the recombinant plasmid, pMS363, containing a 4.1-kb DNA insert that includes the extended-spectrum beta-lactamase gene. Plasmid pMS363 was introduced into the P. aeruginosa PAO strain or into six species of Enterobacteriaceae, and the specific activities of the beta-lactamase and MICs of various beta-lactam antibiotics were estimated. The cloned gene was capable of expression in these strains and caused resistance to carbapenem, penem and other beta-lactam antibiotics, with the exception of aztreonam.

Cloning, Molecular↗