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G Vedel

Publications and source records attributed to G Vedel.

At least 19 recordsLinked to original sources
PubMed2005

Simple method to determine beta-lactam resistance phenotypes in Pseudomonas aeruginosa using the disc agar diffusion test.

BACKGROUND: Pseudomonas aeruginosa is a major opportunistic bacterial pathogen in nosocomial infections because of the increasing prevalence of resistance to many of the commonly used antibiotics. To ensure optimal efficiency of antibiotic treatment against this species, antibiotic susceptibility tests must be interpreted with caution. Most microbiologists now consider it essential to characterize the antibiotic resistance expressed by isolates. Particular resistance mechanisms may be suspected when the bacterium is resistant to several antibiotics in the same family (for example beta-lactam agents). METHODS: Using the disc agar diffusion test, a simple method was developed to distinguish between the common beta-lactam resistance phenotypes of P. aeruginosa and, consequently, the possible resistance mechanism(s). Over a period of 5 years, we analysed 6300 P. aeruginosa strains isolated from various pathological specimens collected from different wards of Cochin Port-Royal Hospital, and reference and collection strains. Each strain had the wild-type phenotype or an acquired resistance phenotype. Eight anti-pseudomonal beta-lactams (ticarcillin, cefotaxime or moxalactam, cefepime or cefpirome, imipenem, ceftazidime, aztreonam, cefsulodin and ticarcillin + clavulanic acid) were used as phenotypic markers. RESULTS: The following markers were sufficient to distinguish between the wild-type phenotype and the various acquired resistance phenotypes: beta-lactamase synthesis, reduced cell wall permeability and/or increased expression of efflux transporters (active efflux). Detection of resistance phenotypes allows 'interpretive reading' of antibiotic susceptibility tests. CONCLUSIONS: Clearly, improved interpretation of antibiotic susceptibility tests is important for a better appreciation of the effect of antimicrobial agents on bacteria such as P. aeruginosa.

Anti-Bacterial Agents↗
PubMed2001

Catalytic and structural properties of IRT-21 beta-lactamase (TEM-77) from a co-amoxiclav-resistant Proteus mirabilis isolate.

Proteus mirabilis strain MAG1, a clinical isolate that is resistant to broad-spectrum penicillins and co-amoxiclav, produces inhibitor-resistant TEM (IRT)-21, a novel mutant of TEM beta-lactamase. This enzyme has a pI of 5.2 and is derived from the bla(TEM-1a) gene ancestor. It contains two major amino acid substitutions specific for co-amoxiclav resistance (Leu-69 for Met and Ser-244 for Arg) that have never been found together previously. The dramatic loss of sensitivity to clavulanic acid, the enhancement of K(m) for all beta-lactams and markedly for ticarcillin, and the decrease in the catalytic efficiency makes IRT-21 comparable to the other IRTs with substitutions at position 244 or double substitutions.

Amoxicillin-Potassium Clavulanate Combination↗
PubMed1996

Evaluation of an expert system linked to a rapid antibiotic susceptibility testing system for the detection of beta-lactam resistance phenotypes.

Interpretive reading of antibiotic disc agar diffusion tests indicates the resistance mechanisms, if any, expressed by a bacterium. An expert system for determining resistance mechanisms using rapid automated antibiotic susceptibility tests has been developed. The beta-lactam susceptibility of each of 300 strains of clinically significant species of enterobacteria, displaying natural and acquired resistance mechanisms, was determined by disc agar diffusion and by a rapid automated method of susceptibility testing associated with an expert system. For every strain, the conclusion of the expert analysis of the automated test was compared with the commonly accepted interpretation of disc agar diffusion tests. Of the 300 strains studied, 275 were similarly interpreted (91.7% agreement). The susceptible and naturally beta-lactam-resistant phenotypes (wild phenotypes) were equally recognized by both methods. Similarly, the results of the two methods concurred for most of the acquired resistance phenotypes. However, for 25 strains (8.3%) the results diverged. The expert system proposed an erroneous phenotype (5 strains), several phenotypes including the correct one (17 strains), or no phenotype (1 strain). For 2 strains the natural resistance mechanism was not detected at first by the automated method but was subsequently deduced by the expert analysis according to bacterial identification. These results demonstrate that satisfactory interpretive reading of automated antibiotic susceptibility tests is possible in 4 to 5 hours but requires careful selection of the antibiotics tested as phenotypic markers.

Anti-Bacterial Agents↗
PubMed1996

In-vitro activity of cephalosporins alone and combined with sulbactam against various strains of Acinetobacter baumannii with different antibiotic resistance profiles.

The beta-lactamases of six strains of Acinetobacter baumannii were investigated using analytical isoelectric focusing, and the MIC values for 16 beta-lactam antibiotics determined against the strains. Three strains produced a chromosomal cephalosporinase (pI > 8.5), one strain a CARB-5 beta-lactamase (pI = 6.35), one strain a TEM-1 penicillinase (pI = 5.4) as well as a cephalosporinase (pI > 8.5), and one carbapenem-resistant strain a beta-lactamase with a pI > 8.5. Ceftazidime, cefepime, cefpirome, imipenem and meropenem were found to be the most effective beta-lactams against five strains. Sulbactam was active against four of the strains at 1-4 mg/L and showed enhanced killing effects with cefpirome.

Acinetobacter↗
PubMed1996

In-vitro bactericidal activity of cefpirome in combination with vancomycin against Staphylococcus aureus and coagulase-negative staphylococci.

In an in-vitro study of the bactericidal activity of cefpirome in combination with vancomycin against 11 clinical isolates of staphylococci, cefpirome at a concentration of 0.25 times the MIC acted synergistically with vancomycin (at a concentration of 0.5, 1 or 2 times the MIC) against Staphylococcus aureus and coagulase-negative staphylococci susceptible or resistant to methicillin. Moreover, increasing the cefpirome concentration to 0.5 or 1 times the MIC combined with vancomycin at the same concentration (0.5 or 1 times the MIC) improved the bacterial killing rate; a bactericidal effect was obtained in 9 or 24 h instead of in 24 or 48 h, respectively.

Anti-Bacterial Agents↗
PubMed1995

Acinetobacter baumannii outbreak isolates characterized by three typing methods.

Forty-two strains of Acinetobacter baumannii were isolated from 15 patients hospitalized in a French intensive care unit. An epidemiological study based on the typing of these isolates was carried out using biotyping, antibiotyping, and ribotyping to recognize the transmission of multiresistant strains by transfer of a patient from one hospital to another. Fifteen strains from the outbreak (1 strain for each patient), five Acinetobacter baumannii strains isolated before the outbreak in Bellevue Hospital (St. Etienne), and five strains isolated in Cochin Hospital (Paris) were included. The three methods gave a good correlation: the epidemic strains had the same antibiotic resistance pattern, the same biotype, and the same ribotypes obtained with three different endonucleases.

Acinetobacter↗
PubMed1994

Nucleotide sequences of the genes coding for the TEM-like beta-lactamases IRT-1 and IRT-2 (formerly called TRI-1 and TRI-2).

Two blaTEM-like genes were characterized that encoded IRT beta-lactamases (previously called TRI) in clinical isolates of Escherichia coli resistant to amoxycillin alone and to combinations of amoxycillin with beta-lactamase inhibitors. Plasmids carrying this resistance were isolated from E. coli K 12 transconjugants and the genes were sequenced after amplification of defined fragments, using TEM-1-specific primers. The gene for IRT-1 beta-lactamase resembled the blaTEM-1B gene, and that for IRT-2 resembled blaTEM-2. However, both IRT enzymes have a glutamine residue at position 37, which is characteristic of TEM-1. The unique nucleotide difference with parental genes corresponding to amino acid variation was observed at nucleotide position 929. The consequence of C to T transition in the blaIRT-1 gene and C to A transversion in the blaIRT-2 gene was the substitution of arginine 241 in the native protein by cysteine and serine, respectively, in the mutants. Thus, the nature of amino acid 241 is critical in conferring resistance or susceptibility to beta-lactamase inhibitors. Furthermore, these basic to neutral amino acid replacements explain the more acidic pI (pI = 5.2) of these IRT enzymes compared to that of TEM-1 (pI = 5.4). The presence of cysteine-241 in IRT-1 also explains the selective sensitivity of this beta-lactamase to inhibition by p-chloromercuribenzoate.

Amoxicillin↗
PubMed1992

Two variants of transferrable extended-spectrum TEM-beta-lactamase successively isolated from a clinical Escherichia coli isolate.

In a leukaemic patient presenting a septicaemia treated with ceftazidime and amikacin, two clinical Escherichia coli isolates distinguished by their level of resistance to oxyimino-beta-lactams were isolated at an interval of 24 h. The isolates were identified by biotyping and esterase electrophoretic typing and the two host strains were shown to be identical. However, each of these strains exhibited a different transferrable extended-spectrum beta-lactamase. These enzymes had different pI values (5.25 and 5.58), but were both blaTEM-1 mutants. The enzyme with pI 5.25 was identical to TEM-101 (TEM-12) (serine 162 substitution). The enzyme with pI 5.58 showed an additional amino acid substitution (lysine residue instead of an arginine at position 237) and was denominated TEM-23. These data indicate that point-mutations can be successively cumulated in vivo by blaTEM mutants, leading to expression of beta-lactamases with increased hydrolysis rates.

Bacterial Typing Techniques↗
PubMed1992

Clinical isolates of Escherichia coli producing TRI beta-lactamases: novel TEM-enzymes conferring resistance to beta-lactamase inhibitors.

Two different strains of Escherichia coli exhibiting unusual patterns of resistance to beta-lactam antibiotics were isolated from patients at Cochin Hospital. Both isolates showed a low level of resistance to amoxycillin, ticarcillin and ureidopenicillins but were susceptible to cephalosporins, aztreonam and imipenem; beta-lactamase inhibitors potentiated the activities of the beta-lactams to only a limited extent. All resistance characteristics of the strains were transferable by conjugation to E. coli K12. Resistance was shown to be due to beta-lactamases of pI 5.20 and relative molecular masses of 24,000. The hydrolytic and inhibition profiles of these enzymes were similar to each other but differed from those of broad-spectrum beta-lactamases (TEM-1). The rates of hydrolysis (Vmax) of amoxycillin (c. 200%) were higher than that for TEM-1 (84%). Ticarcillin, ureidopenicillins and cephaloridine were hydrolyzed slowly. However, as for TEM-1, no hydrolysis was observed with cefoxitin, third generation cephalosporins, aztreonam and imipenem. The high Km values demonstrated the poor affinity of these enzymes for their substrates. Unlike TEM-1, they were poorly inhibited by beta-lactamase inhibitors. These two enzymes differed from each other as follows: (i) the concentrations of clavulanic acid required for 50% beta-lactamase inhibition were 31 mumol/L for one enzyme (E-SAL) and 9.4 mumol/L for the other (E-GUER); (ii) p-chloromercuribenzoate was a more active inhibitor of E-SAL then E-GUER. The titration curve method and DNA-DNA hybridization studies demonstrated that both enzymes were structurally related to TEM-1. The novel plasmid-encoded enzymes produced by the two isolates of E. coli appeared to be almost identical and to be derived from TEM-enzymes. On the basis of their presumed phylogeny and their biological properties, we propose that these beta-lactamases be given the generic name TRI (TEM Resistant to beta-lactamase Inhibitors).

Anti-Bacterial Agents↗
PubMed1992

Clostridium perfringens septicemia during the course of leukemia.

Clostridium perfringens (CP) is an infrequent cause of septicemia in neutropenic patients. We report the case of a 17 year old man treated for acute lymphoblastic leukaemia in whom a strain of CP was isolated from blood cultures. The clinical spectrum and evolution of CP septicemia in neutropenic patients are discussed.

Adolescent↗
PubMed1990

Failure of teicoplanin therapy in two neutropenic patients with staphylococcal septicemia who recovered after administration of vancomycin.

A report is given on two neutropenic patients with staphylococcal septicemia caused by Staphylococcus haemolyticus and Staphylococcus aureus (both strains methicillin-resistant) who failed to respond to therapy with teicoplanin. Both strains were resistant to teicoplanin (MIC 16 and 8 mg/l respectively), but remained sensitive to vancomycin (MIC 2 and 4 mg/l respectively). Replacement of teicoplanin with vancomycin led to full recovery of both patients and their discharge from hospital. These two cases emphasize the importance of clinical and microbiological monitoring of patients with staphylococcal septicemia, even when glycopeptides are used for treatment.

Adult↗
PubMed1990

Prevalence of Staphylococcus aureus and coagulase-negative staphylococci with decreased sensitivity to glycopeptides as assessed by determination of MICs.

The prevalence of staphylococci with decreased sensitivity to glycopeptides was assessed at a Paris hospital by determination of the MICs. The values obtained using the MIC method were compared to those obtained using the routine disk agar diffusion method. One hundred independently isolated strains were tested including 57 Staphylococcus aureus isolates and 43 coagulase-negative staphylococci (CNS). For all strains vancomycin MICs were less than or equal to 4 mg/l but for 5.3% of the Staphylococcus aureus isolates and 25.6% of the CNS isolates teicoplanin MICs were high (greater than or equal to 8 mg/l). Moreover, teicoplanin MICs did not correlate well with zone sizes. The MIC method is therefore recommended for evaluating the susceptibility of staphylococci to teicoplanin.

Anti-Bacterial Agents↗
PubMed1989

Biochemical, immunological and physicochemical comparisons between OHIO-1 and four SHV-type beta-lactamases.

The biochemical, immunological and physicochemical properties of the beta-lactamase OHIO-1 were compared to those of four beta-lactamases commonly found in Klebsiella pneumoniae: SHV-1, SHV-3 and the beta-lactamases of strains GN 11-03 and GN 422. The substrate profile of SHV-1, OHIO-1 and of the beta-lactamases GN 11-03 and GN 422 were similar, while that of SHV-3 appeared comparable to that of the extended spectrum SHV-2. Moreover, anti-TEM-1 serum inactivated OHIO-1 as well as SHV-1 and the beta-lactamases of strains GN 11-03 and GN 422. Analysis of the electrophoretic mobilities, isoelectric points and titration curves demonstrated that OHIO-1 and the 4 other beta-lactamases examined were closely related variants. From these findings it appears that OHIO-1 could be classified among the SHV-type beta-lactamases.

Electrophoresis↗
PubMed1989

The analysis of five carbenicillin-hydrolysing enzymes by electrophoretic methods.

Five carbenicillin-hydrolysing enzymes (carbenicillinases, or CARB), PSE-4 (CARB-1), PSE-1 (CARB-2), CARB-3, CARB-4 and CARB-5, and the beta-lactamase PSE-2 were compared by analysing their isoelectric points (pI), electrophoretic mobilities (mR) and titration curves (pH gradient electrophoresis). The pI determined by isoelectric focusing were 4.3 (CARB-4), 5.3 (PSE-4/CARB-1), 5.7 (PSE-1/CARB-2), 5.75 (CARB-3), 6.1 (PSE-2) and 6.35 (CARB-5). Their mR were estimated by zone electrophoresis as congruent to 26 for PSE-1 (CARB-2), CARB-3 and CARB-5, congruent to 30 for PSE-2, congruent to 33 for PSE-4 (CARB-1) and congruent to 61 for CARB-4. Titration curve analyses indicated that (1) PSE-4 (CARB-1), PSE-1 (CARB-2), CARB-3 and CARB-5 are closely related variants differing by a few amino acid substitutions; (2) the qualitative titration curve of CARB-4 is different from those of PSE-4 (CARB-1), PSE-1 (CARB-2), CARB-3 and CARB-5, although their patterns are somewhat similar; and (3) PSE-2 has no structural relationship with any of the other carbenicillin-hydrolysing enzymes or carbenicillinases (CARB) studied. Electrophoretic methods, and in particular titration curve determination combined with other physicochemical and enzymatic data, allowed a rapid comparison of the molecular structures of the beta-lactamases, and hence their classification.

Acinetobacter↗
PubMed1989

Analysis of the molecular relatedness of four extended spectrum beta-lactamases (SHV-2, SHV-3, SHV-4 and SHV-5) by comparative protein titration curves.

Six beta-lactamases from Klebsiella pneumoniae, five of which (SHV-1, SHV-2, SHV-3, SHV-4 and SHV-5) were plasmid-encoded and one which (beta 1a GN 11-03) was chromosomally-encoded, were compared by analysis of their isoelectric points (pI), electrophoresis mobilities (MF) and titration curves or pH gradient electrophoresis. Four groups were defined by their pI and MF, namely SHV-1 and SHV-2 (pI = 7.6, MF approximately 14), SHV-3 and beta 1a GN 11-03 (pI = 7.0, MF approximately 20), SHV-4 (pI = 7.8 MF approximately 12) and SHV-5 (pI = 8.2, MF approximately 5). The titration curves of SHV-1 and SHV-2 enzymes on the one hand, and SHV-3 and beta 1a GN 11-03 on the other were completely superimposable for the whole of the pH gradient (3.5-10), indicating strongly similarity. Conservative amino-acid substitutions could account for the differences in the substrate spectra of the purified enzymes. The differences observed between the titration curves of the enzymes SHV-1/SHV-3, SHV-1/beta 1a GN 11-03, SHV-2/SHV-3 and SHV-5/SHV-4 pairs were consistent with the replacement of a basic amino-acid residue in the former enzyme of each pair by an acidic residue in the latter. Similarly, the titration curves of SHV-1/SHV-4 and of SHV-2/SHV-4 pairs may suggest the replacement of an acidic amino-acid in the former beta-lactamases by a neutral amino-acid in the latter of each pair. However, the presence of several self-cancelling or neutral substitutions is also possible. In contrast, when SHV-1 and TEM-1 (pI = 5.4 MF approximately 45) were titrated together, no structural relationship could be inferred.

Chromosomes, Bacterial↗