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R Labia

Publications and source records attributed to R Labia.

At least 163 records · Page 9Linked to original sources
PubMed1979

[Activity of cefamandole against enterobacteria resistant to cephalosporins (author's transl)].

Cefamandole is a new cephalosporin active against non beta-lactamase producing enterobacteria, at lower concentrations (mean of MIC: 0.79 mcg/ml) than those of cefalothin taken as a reference amongst current cephalosporins (mean of MIC: 6.84 mcg/ml). This improved activity was also seen against enterobacteria producing extra-chromosomal penicillinase (mean of MIC: 3.59 mcg/ml for cefamandole and 12.76 mcg/ml for cefalothin). These findings would suggest that cefamandole is better able to reach the site of action of beta-lactamines within the bacteria. In contrast to current cephalosporins, cefamandole is active against enterobacteria producing chromosomal cephalosporinase, by virtue of its stability against the hydrolytic activity of this type of enzyme. It thus is the leader of a new generation of cephalosporins.

Cefamandole↗
PubMed1979

["Beta-lactamase enzymogram": an agar adaptation of the iodometric method (author's transl)].

This paper deals with an agar-gel adaptation of the Perret-Novick iodometric titration of degradation products from beta-lactam antibiotics when they are submitted to a beta-lactamase action. Petri dishes containing an agar-gel make up from the classical iodine-iodide-starch system, initially present a dark blue colour. When beta-lactam compounds are opened by beta-lactamases from crude extracts or whole bacteria, the gel is locally destained. Two experimental variants of this procedure are proposed. This semi-quantitative, inexpensive, accurate and simple method is very convenient for routine experiments. Thus with crude extracts or even whole cells, information can be obtained about beta-lactamase specific activities, substrate profils or activity of inhibitors such as cloxacillin or clavulanic acid.

Agar↗
PubMed1978

[Kinetics of beta-lactamase inhibition by clavulanic acid].

The mechanisms of action of 3 R-factors on beta-lactamases (penicillin amido-beta-lactamhydrolase, EC 3.5.2.6) (TEM-1 pI = 5.4, TEM-2 pI = 5.6 and Pitton's type 2 pI = 7.7) have been kinetically analyzed for clavulanic acid inactivation. Clavulanic acid appears as a competitive and irreversible inhibitor (Kcat inhibitor) reacting in two steps: a, formation of a reversible enzyme . inhibitor complex (characterized by a Ki); b, evolution of the reversible complex into a new derivative (covalent, stable and inactive) by monomolecular kinetics characterized by a k6 (or Kcat) related to half-life. The kinetic constants are: TEM-1: Ki = 0.8 micrometer, k6 = 0.027 s-1; TEM-2: Ki = 0.7 micrometer, k6 = 0.03 s-1; type 2: Ki = 0.6 micrometer, k6 = 0.046 s-1. These results justify the 'progressive irreversible' character of the inhibition generally described.

Anti-Bacterial Agents↗
PubMed1978

Beta-lactamases: determination of their isoelectric points.

Important discrepancies in isoelectric points (pI) of beta-lactamases were observed depending on the experimental procedure used for their determination: isoelectric focusing (IEF) in sucrose density gradients or analytical IEF in thin-layer polyacrylamide gels (PA). The variations, negligable in the case of TEM-like beta-lactamases, appeared to be important in the case of cephalosporinases and are related to an artifact which appears in PA-IEF. This has been clearly shown with beta-lactamase preparations from the following bacterial strains: Pseudomonas aeruginosa NCTC 8203 (pI = 8.7), P. aeruginosa NCTC 10701 (pI = 9.4), and Proteus morganii NCTC 235 (pI = 8.3). The data previously obtained by PA-IEF were much lower.

Amidohydrolases↗
PubMed1978

Novel beta-lactamase from Branhamella catarrhalis.

A strain of Branhamella catarrhalis isolated from sputum was shown to be resistant to penicillin and ampicillin. This strain produced a beta-lactamase which has been judged to be a novel enzyme, on the basis of substrat profil, isoelectric point and location of genetic determinant.

Ampicillin↗
PubMed1977

[Problems in the determination of isoelectric points of beta lactamases].

Analytical isoelectric focusing in polyacrylamide gels and preparative electrofocusing in density gradients may give very different pI determination for the same beta lactamase. This difference seems due to a lack of enzyme migration in some parts of the cross-linked polyacrylamide gel. This migration appears easier in density gradient isoelectricfocusing, and thus this technique yields more significant absolute pI values. Analytical isoelectric focusing should only be used for comparison studies.

Amidohydrolases↗
PubMed1977

Beta-lactamases produced by a Pseudomonas aeruginosa strain highly resistant to carbenicillin.

A Pseudomonas aeruginosa strain isolated at Besançon Hospital, France, proved to be highly resistant to carbenicillin and showed a high hydrolytic activity toward this antibiotic. We clearly demonstrated that two beta-lactamases were synthetized: one of them, constitutive, has its enzymatic activity directed mainly toward penicillins, and carbenicillin appears to be its best substrate (higher V(max)); thus, this beta-lactamase is a "carbenicillinase" that differs from the well-known "TEM-like" enzymes. The isoelectric point of this carbenicillinase is 5.30 +/- 0.03. The other one is an inducible cephalosporinase, very similar to the cephalosporinases usually found in these organisms. Its isoelectric point is 8.66 +/- 0.04. These two enzymes have been separated by affinity chromatography and isoelectric focusing. The kinetic constants were measured by computerized microacidimetry.

Amidohydrolases↗
PubMed1977

[Microheterogeneity of R plasmid coded beta-lactamases in analytical isoelectric focusing (author's transl)].

Analytical isoelectric focusing of plasmid-coded beta-lactamases in polyacrylamide gels gives rise to several satellite bands in addition to one major active band (microheterogeneity). When the R plasmids are transferred by conjugation into 4 different bacterial species (Escherichia coli, Klebsiella pneumoniae, Salmonella typhi-murium, Proteus mirabilis) the position of the main band remains constant, but the number and position of the satellite bands are changed. Furthermore, the minimal inhibitory concentrations of several beta-lactamines are also changed when the plasmids are transferred between these different host strains. These facts suggest that the bacterial host might modify the physical structure and the activity of plasmid-determined beta-lactamases. They also suggest that identification of beta-lactamases and comparison of their isoelectric focusing patterns should always be carried out using the same bacterial host strain.

Amidohydrolases↗
PubMed1976

[Multiplicity of beta lactamases: a problem of isoenzymes].

Analytical isoelectric focusing of beta lactamases is a very sensitive and powerful technique which generally shows a number of satellites near the main enzymatic spike. By this technique we studied two bacterial groups known to produce different beta lactamases, but only one by germ. Analytical isoelectric focusing showed that all bacteria from the same group produce the same satellite system which differs only in relative activity.

Amidohydrolases↗
PubMed1976

[Inducible cephalosporinases from Proteus morganii].

It has been shown that two Proteus morganii strains produce an inducible cephalosporinase. No significative difference was shown between them: they present the same isoelectric poit: 8,3 and very similar kinetic constants. The parameter tau, proportional to the half life of antibiotic at low concentration, in presence of beta lactamase, shows that cefamandole is the most stable cephalosporin studied.

Amidohydrolases↗
PubMed1976

[Nature of the inhibition of some cephalosporinases by carbenicillin].

This paper deals with the kinetic inhibition of six cephalosporinases (cephalosporin amido-beta-lactamhydrolase, EC 3.5.2.8) by carbenicillin. In previous cases, the inhibition has appeared usually to be competitive and slowly reversible. This makes it possible to measure the two terms of the ratio Ki=k5/k4;k4 and k5 being respectively the velocity constants of formation and destruction of the enzyme-inhibitor complex. A program was prepared which made it possible to obtain these constants from only one experiment. With ampicillin and cloxacillin, we verified that the reaction is faster, and that only Ki can be measured. These facts suggest that special precautions should be taken in order to obtain signigicant values for the constants governing inhibition.

Amidohydrolases↗
PubMed1976

[Kinetics of a new cephalosporinase from Pseudomonas aeruginosa].

Pseudomonas aeruginosa strain RL 39 produces an inducible cephalosporinase possessing an isoelectric point of 8,66. The kinetic constants have been measured by computerized microacidimetry. The results allow to differenciate this enzyme from the one produced by Ps. aeruginosa GN 918 (Yaginuma et al. (1973) Jap. J. Microbiol., 17, 141-149) showing a similar isoelectric point.

Amidohydrolases↗
PubMed1975

Kinetic studies of a beta-lactamase by a computerized microacidimetric method.

On-line computerized treatment of enzyme kinetic data allows the precise measurement of Michaelis--Menten constants (Km and V) from a single progress curve. This method has been used to determine the kinetic constants of a beta-lactamase extracted from an Escherichia coli strain. In the profile of enzymatic activity there obtained, Km and V are a function of the pH. From these results some information is derived about the mechanism of the enzyme--substrate binding.

Anions↗
PubMed1975

[Identification of the beta lactamase R-TEM of Pseudomonas aeruginosa].

This paper is dealing with the enzymatic problem raised by two strains of Ps. aeruginosa resistant to classical beta lactam antibiotics including carbenicillin. These two strains hydrolyse all these antibiotics. In both cases, we have shown the simultaneous biosynthesis of two enzymes: an inducible and chromosome cephalosporinase frequently found in this germ, and a constitutive beta lactamase, with a penicillinase activity which has been identified with the extrachromosomic beta lactamase R-TEM. These two enzymes have been separated by affinity chromatography, characterized by their kinetic constants given by computerized microacidimetry, and their isoelectric points which are respectively 9.2 for the cephalosporinase and 5.40 for the penicillinase R-TEM. Isoelectric focussing also shows the separation of these two enzymes.

Amidohydrolases↗