Beat note stabilization in dual-polarization DFB fiber lasers by an optical phase-locked loop.

A fully fibered microwave-optical source at 1.5 µm is studied experimentally. It is shown that the beat note between two orthogonally polarized modes of a distributed-feedback fiber laser can be efficiently stabilized using an optical phase-locked loop. The pump-power-induced birefringence serves as the actuator. Beat notes at 1 GHz and 10 GHz are successfully stabilized to a reference synthesizer, passing from the 3 kHz free-running linewidth to a stabilized sub-Hz linewidth, with a phase noise as low as -75 dBc/Hz at 100 Hz offset from the carrier. Such dual-frequency stabilized lasers could provide compact integrated components for RF and microwave photonics applications.

Beta-lactamase stability of imipenem.

The beta-lactamase stability and interactions of imipenem were analysed in comparison with those of cefazolin, cefuroxime, cefoxitin, cefotaxime, ceftazidime, mezlocillin, piperacillin and penicillin G for a set of representative beta-lactamases. These enzymes included penicillinases such as those obtained from Staphylococcus aureus, Escherichia coli and other Enterobacteriaceae (TEM-1 and similar enzymes) (group A); cephalosporinases produced by Esch. coli (Amp C type), Serratia liquefaciens, Enterobacter cloacae, Pseudomonas aeruginosa (group B); and beta-lactamases produced by Klebsiella spp., Proteus vulgaris and Bacteroides fragilis and with a high hydrolytic activity for the newer cephalosporins (group C). Enzymes of group A were demonstrated to be highly active against penicillins and also against the early cephalosporins; enzymes of group B showed hydrolytic activity for all other tested compounds, including the newer cephalosporins and cephamycins, but not imipenem, whereas enzymes of group C were highly active against the new cephalosporins but not against cephamycins and imipenem. In conclusion, imipenem shows a moderate affinity for all these enzymes but no detectable hydrolysis.

[Klebsiella oxytoca beta-lactamases: study of their action on 3d-generation cephalosporins]. / Bêtalactamases de Klebsiella oxytoca: étude de leur action sur les céphalosporines de troisième génération.

Indole-positive Klebsiella pneumoniae or K. oxytoca are usually resistant to penicillins as a result of the production of a chromosomally-mediated beta-lactamase with a low level of synthesis (specific activity approximately 50 to 100 mU/mg). Although most strains are susceptible to the majority of cephalosporins, some strains exhibit resistance to cephalosporins including third-generation drugs. These resistant strains produce a chromosomally-mediated beta-lactamase with a high level of synthesis (specific activity approximately 5,000 mU/mg or higher). Four beta-lactamases have been identified on the basis of their isoelectric points: pI = 5.5, 5.7, 6.0 and 6.3; nevertheless they have similar kinetic constants, and are inhibited by clavulanic acid. These enzymes hydrolyze most third-generation cephalosporins, in the following order of decreasing velocities: cefoperazone, ceftriaxone, cefotaxime, cefodizime, cefpirome; ceftazidime, and cefoxitin, cefotetan, latamoxef, cephamycins which are totally resistant to these enzymes.

[Epidemiologic study of intestinal and urinary bilharziasis in the Tala Mokolo region (Mandara Mountains, North Cameroon)]. / Etude épidemiologique des bilharzioses intestinale et urinaire dans la région de Tala Mokolo (Monts Mandara, Nord Cameroun).

In the Mandara Mountains, where small dams have been erected, people living in the Tala Mokolo district eliminate some S. haematobium eggs in 31,4% of urines samples, and some S. mansoni eggs in 38,1% of stools samples. Evaluated from hemagglutination test, bilharziosis prevalence reaches 55,7%. Male subjects are more frequently affected than female subjects, particularly as for as intestinal bilharziosis is concerned. Urinary bilharziosis prevalence or intestinal bilharziosis prevalence are subject to proximity of small water reservoirs mostly infested either by Bulinus globosus or Biomphalaria pfeifferi. These small water reservoirs are mainly "mayo" head-bays.

[Affinity of N-formimidoyl-thienamycin (MK-0787) for beta-lactamases, analysis by a statistical method: correspondence analysis]. / Affinité de la N-formimidoyl-thiénamycine (MK-0787) pour les bêta-lactamases, étude par une méthode statistique: analyse des correspondances.

N-formimidoyl-thienamycin (MK-0787) is not subject to beta-lactamase hydrolysis. Nevertheless, this compound does show some affinity for the TEM-type penicillinases, cephalosporinases and a few other beta-lactamases. Surprisingly no affinity was found for the penicillinases of the CARB-type. The results thus obtained for affinity constants Ki and Km were submitted to a statistical analysis treatment, i.e. correspondence analysis and hierarchic ascendent classification. This confirms the fact that MK-0787 presents an unusual behaviour towards beta-lactamases.

Semi-quantification of a microbiological method using beta-lactamases in detecting the hydrolysis of beta-lactam antibiotics.

The so-called "double disc" technique of Masuda et al. for detecting the hydrolysis of beta-lactams by beta-lactamases was semi-quantified. This semi-quantification consisted of using beta-lactamase preparations progressively diluted by a factor of ten. The last dilution producing a detectable hydrolysis of the antibiotic was thus noted. By using the species Escherichia coli (potentially cephalosporinase producer) as a model, we studied the possible applications of this method. Due to its great sensitivity it was possible to analyse and appreciate the degradation of some cephalosporins reputedly resistant to beta-lactamases, such as cefoxitin, cefuroxime, cefamandole and cefotaxime. The carboxy-penicillins (carbenicillin and ticarcillin) were the most stable beta-lactams towards the cephalosporinase of E. coli 0002.

Behaviour of ceftazidime towards beta-lactamases.

from Escherichia coli, Enterobacter cloacae, Proteus morganii and Pseudomonas aeruginosa, but the geometric mean of the inhibition constant Ki used to measure this interaction was 120 and almost 700 times higher with ceftazidime than with cefotaxime and cefuroxime, respectively. Two other beta-lactamases isolated from Pr. vulgaris and Klebsiella oxytoca also showed little or no interaction with ceftazidime. A complementary microbiological technique, the "double-disc" technique, indicated that ceftazidime was more stable than cefotaxime to all beta-lactamases tested. Moxalactam, however, appeared to have slightly greater stability.

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.

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.

[Inducible cephalosporinases from Proteus morganii]. / Céphalosporinases inductibles de 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.

[Kinetics of a new cephalosporinase from Pseudomonas aeruginosa]. / Etude cinétique d'une nouvelle céphalosporinase de 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.