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Biomedical subjects

A Philippon

Publications and source records attributed to A Philippon.

At least 91 records · Page 5Linked to original sources
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↗
PubMed1989

In-vitro activity of FCE 22101 and other beta-lactam antibiotics against Enterobacteriaceae resistant to third generation cephalosporins.

The in-vitro activity of FCE 22101 was compared with those of imipenem, aztreonam, cefotaxime, ceftriaxone and latamoxef against 225 Enterobacteriaceae (209 clinical isolates and 16 derivatives of Escherichia coli K12) chosen for their resistance (MIC greater than or equal to 8 mg/l) to third-generation cephalosporins. The beta-lactamases produced by the strains of Enterobacter cloacae, Klebsiella pneumoniae and Esch. coli were identified. The mean MICs of FCE 22101 were 2-8 mg/l for Ent. cloacae, Citrobacter freundii and Morganella morganii. For Ent. cloacae, the MICs were slightly higher for the cephalosporinase non overproducing (5.5-8 mg/l) than for the cephalosporinase overproducing (4.5 mg/l) strains. The mean MIC was 9 mg/l for Serratia spp. but for half of the strains the MICs were greater than or equal to 16 mg/l. The MICs of FCE 22101 were 0.5-1 mg/l for the resistant clinical isolates or isogenic derivatives of K. pneumoniae and Esch. coli producing extended broad-spectrum beta-lactamases (SHV-2, SHV-3 or CTX-1), whether measured in the presence of clavulanate or not, and against the sensitive controls. This showed that the compound was not affected by these new beta-lactamases. The MICs of imipenem, on the average four to five times lower than those of FCE 22101, were found to be very similar for resistant and sensitive strains. The MICs of aztreonam were high (32-128 mg/l) for C. freundii, K. oxytoca and cephalosporinase overproducing strains of Ent. cloacae. There was cross-resistance between the third-generation cephalosporins, but the MICs of latamoxef remained low (1 mg/l) against M. morganii, Klebsiella spp. and Esch. coli.

Carbapenems↗
PubMed1989

Novel carbenicillin-hydrolyzing beta-lactamase (CARB-5) from Acinetobacter calcoaceticus var. anitratus.

A strain of Acinetobacter calcoaceticus var. anitratus highly resistant to ticarcillin but susceptible to ticarcillin in combination with clavulanic acid (2 mg/l) was found to produce a constitutive beta-lactamase. This enzyme was periplasmic with a characteristic substrate profile of a carbenicillin-hydrolyzing enzyme. Enzyme inhibition was detected with antiserum (anti-CARB-3), pCMB, cloxacillin, clavulanic acid and sulbactam. This novel enzyme with a molecular mass of 28,000 resembles other plasmid-mediated carbenicillinases (CARB) but differs in its apparent isoelectric point estimated as 6.3 and has been designated CARB-5 on this basis.

Acinetobacter↗
PubMed1989

Molecular characterization of the gene encoding SHV-3 beta-lactamase responsible for transferable cefotaxime resistance in clinical isolates of Klebsiella pneumoniae.

In Klebsiella pneumoniae 86-4, cefotaxime resistance was due to a transferable broad-spectrum beta-lactamase, SHV-3. The plasmid-borne gene encoding SHV-3 has been cloned, and the primary structure of the enzyme was deduced from its nucleotide sequence. SHV-3 differs from SHV-1 in two positions. The extended substrate profile of SHV-3 probably results from the substitution of Ser-213 for Gly, as in SHV-2, whereas replacement of Arg-180 by Leu resulted in a decrease in the pI from 7.6 to 7.0. The blashv-3 gene is highly homologous (92% DNA sequence identity) with the chromosomal gene coding for LEN-1 beta-lactamase of K. pneumoniae, suggesting that the origin of the SHV-encoding genes now present on many plasmids may be chromosomal.

Base Sequence↗
PubMed1989

[In vitro and in vivo activity of a combination of clavulanic acid and amoxicillin against Klebsiella pneumoniae producing extended broad-spectrum betalactamase (CTX-1, SHV-3, SHV-4)].

In vitro activity of an aminopenicillin (amoxicillin or ampicillin) combined with a betalactamase inhibitor (clavulanic acid or sulbactam, 2 mg/l) was examined against 39 strains of K. pneumoniae producing 3 types of extended broad spectrum betalactamases (CTX-1, SHV-3, SHV-4). Clavulanic acid produces the best synergistic effect. The in vivo activity of Augmentin (amoxicillin + clavulanic acid), 1 g once or twice a day, during 10 +/- 3 days was evaluated on 10 cases urinary tract infections in paraplegic patients. After 3 days, no leucocyturia was observed and bacteria were no more detected. The inhibitory effect of clavulanic acid for the extended broad-spectrum betalactamases shows that such an association could be probably chosen as well for treatment urinary infection.

Amoxicillin↗
PubMed1989

[Broad spectrum beta-lactamases and the API ATB 244 system: the need for detection].

API ATB 24H is an automated system designed to test the sensitivity of bacteria to antibiotics. Using this system we found that it was not fully able to detect acquired resistance to oxy-iminocephalosporins in enterobacteriaceae producing extended broad spectrum betalactamase (CTX-1, SHV-3, SHV-4). However, the frequency of detection varied with the type of API SYSTEM (ATB G-, ATB PSE), the nature of beta lactam antibiotic (cefotaxime, ceftazidime) and the type of beta lactamase produced. Considering the fact that this new mechanism of resistance must be taken into account, we suggest that the most simple method for the detection of oxy-imini beta lactamases is a double disk test of synergy between Augmentin (acid clavulanic + amoxycillin) and 1 disk of oxy-iminocephalosporin.

Cephalosporins↗
PubMed1988

[Plasmid resistance to 3d generation cephalosporins].

Beta-lactamases still play an important part in medical bacteriology, as shown by the emergence, since 1983, of plasmid-mediated beta-lactamases with an enlarged spectrum (SHV-2, CTX-1, etc.). Such enzymes are only produced by enterobacteria and, more specifically, by Klebsiella pneumoniae. This phenomenon, described in Europe and in Africa, is certainly more widespread than it would appear, as some strains are now known to be less sensitive to third generation cephalosporins (MIC 1 to 4 mg/l). Despite differences in behaviour (cefotaximase and ceftazidimase phenotypes), resistance to amino-, carboxy- and ureido-penicillins is associated with reduced sensitivity or resistance to oxyimino beta-lactams (cefotaxime, ceftriaxone, ceftazidime, aztreonam), but cefamycins and imipenem are untouched. Being sensitive to enzyme inhibitors (e.g. clavulanic acid), these beta-lactamases can easily be detected and some infections (notably urinary tract infections) can probably be treated using these inhibitors. These enzymes show modified kinetic constants (better affinity and quicker hydrolysis) against penicillins, third generation aminothiazolimino-cephalosporins and aztreonam. The producing strains are mutants, with aminoacid 1 to 2 substitutions, of those which produce the usual plasmid-borne and transposable beta-lactamases (TEM or SHV). Because these beta-lactamases are plasmid-mediated, enzyme production mechanisms are spreading among enterobacteria species in relation to other resistance markers (tobramycin, netilmicin, amikacin). Strains which produce these new enzymes are mainly isolated from patients treated in intensive care units.

Cell Membrane Permeability↗
PubMed1988

Dissemination in five French hospitals of Klebsiella pneumoniae serotype K25 harbouring a new transferable enzymatic resistance to third generation cephalosporins and aztreonam.

A strain of Klebsiella pneumoniae K25 resistant to newer beta-lactam drugs was isolated in clusters in five hospitals in the Paris area. The MICs of ceftazidime and aztreonam (greater than or equal to 128 mg/l) were higher than that of cefotaxime (16 mg/l) for the strain but, when measured in the presence of clavulanic acid, they were less than or equal to 1 mg/l. The donor strains and derivatives produced a beta-lactamase with a pI of 7.75-7.8 and hydrolysing activity against a wide spectrum of beta-lactams similar to that of SHV-2 and SHV-3, but with significant hydrolysis of ceftazidime. This new enzyme could be designated SHV-4.

Aztreonam↗
PubMed1988

Distribution of beta-lactamases and phenotype analysis in clinical strains of Acinetobacter calcoaceticus.

One hundred clinical strains of Acinetobacter calcoaceticus isolated from 1981 to 1986 were screened for enzymatic resistance to beta-lactam antibiotics. Fourteen beta-lactam antibiotics were tested and four phenotypes were defined on the basis of enzymatic resistance and of susceptibility to the following beta-lactams: ticarcillin, piperacillin, cefotaxime, and ceftazidime. The resistance of A. calcoaceticus to beta-lactam antibiotics was predominantly due to beta-lactamases, which were produced by 81% of the strains. In most (71%) of the beta-lactamase producing strains, a penicillinase of the TEM type was observed; in 9% of the strains, all isolated since 1985, a CARB-type penicillinase with a pI 6.3 was observed. The presence of a cephalosporinase type enzyme was detected in acinetobacter strains isolated since 1981 and its incidence increased in 1986. Multiple beta-lactamases (penicillinase plus cephalosporinase) were observed in 32% of the strains.

Acinetobacter↗