PubMed Health⌕ Search

Biomedical subjects

R Labia

Publications and source records attributed to R Labia.

At least 109 records · Page 6Linked to original sources
PubMed1989

Comparative study of five plasmid-mediated ceftazidimases isolated in Klebsiella pneumoniae.

Five plasmid-mediated beta-lactamases conferring a high level of resistance to ceftazidime were isolated from Klebsiella pneumoniae strains. These ceftazidimases (CAZ) differed in their isoelectric point (from 5.3 to 8.2) and were encoded by large self-transferable plasmids of 85 kb (CAZ-2, CAZ-3) or greater than or equal to 150 kb (CAZ-1, CAZ-4, CAZ-5). The 85 kb plasmids seemed closely related to pCFF04 encoding CTX-1 enzyme and belonged to the same incompatibility group 7 or M. These beta-lactamases hydrolysed all beta-lactams with the exception of cephamycins and carbapenems. For CAZ-1, CAZ-2 and CAZ-3 producers, MICs of ceftazidime (32-256 mg/l) were higher than MICs of cefotaxime (0.12-2 mg/l) and aztreonam (1-16 mg/l). For the strains producing the beta-lactamases CAZ-4 and CAZ-5, MICs of aztreonam were the highest (greater than or equal to 256 mg/l). The impaired activities of cephalosporins and monobactams were restored equally well by 2 mg/l of clavulanate, sulbactam and CL-298741 for CAZ-2 producing strains (wild type and transconjugant). Sulbactam (2 mg/l) had a lower protective effect than other inhibitors on ceftazidime for CAZ-1 and CAZ-3 producing K. pneumoniae. The protective effect of sulbactam (2 mg/l) was lower than that of the other inhibitors on all beta-lactams for CAZ-4 and CAZ-5 producers. The enzymes CAZ-1, CAZ-2 and CAZ-3 derived from TEM beta-lactamase whereas CAZ-4 and CAZ-5 derived from SHV-1 enzyme.

Autoradiography↗
PubMed1989

Interactions of meropenem, with beta-lactamases, including enzymes with extended-spectrum activity against third-generation cephalosporins.

The interactions of a meropenem were studied with a set of beta-lactamases including the new TEM- and SHV-related plasmid-mediated enzymes that have extended-spectrum activity against third-generation cephalosporins ('cefotaximases' and 'ceftazidimases'). Meropenem and imipenem were highly resistant to the hydrolytic activity of all the TEM and SHV related beta-lactamases, and to the OXA enzymes, as were the cephamycins: cefoxitin and cefotetan. The two carbapenems were also highly stable to Class C beta-lactamases (chromosomal cephalosporinases) whereas third-generation cephalosporins and cephamycins were slowly hydrolyzed. Both carbapenems demonstrated quite similar affinities for all the enzymes studied. In some instances, and particularly with Class A (TEM- and SHV-derived) enzymes, meropenem inactivated the beta-lactamase activity. Imipenem appeared less reactive in this respect.

Acylation↗
PubMed1989

Multiplicity of TEM-derived beta-lactamases from Klebsiella pneumoniae strains isolated at the same hospital and relationships between the responsible plasmids.

Five plasmid-mediated beta-lactamases conferring high-level resistance to ceftazidime were isolated from Klebsiella pneumoniae strains in the same hospital. These enzymes had isoelectric points ranging from 5.3 to 6.5 (CAZ-1, 5.55; CAZ-2, 6.0; CAZ-3, 5.3; CAZ-6, 6.5; and CAZ-7, 6.3). All isolates and their Escherichia coli transconjugants were highly resistant to amoxicillin (MICs, greater than 4,096 micrograms/ml), piperacillin (64 to 256 micrograms/ml), cephalothin (32 to 256 micrograms/ml), and ceftazidime (32 to 512 micrograms/ml) but remained moderately susceptible to cefotaxime (0.5 to 8 micrograms/ml). Only CAZ-6- and CAZ-7-producing strains were highly resistant to aztreonam (64 to 128 micrograms/ml). All the isolates remained susceptible to moxalactam and imipenem. The reduced activity of piperacillin, cefotaxime, ceftazidime, or aztreonam was restored by 2 micrograms of clavulanate, sulbactam, tazobactam, or brobactam per ml for E. coli producing CAZ-2, CAZ-3, and CAZ-7. Sulbactam had a lower protective effect than other inhibitors for E. coli harboring CAZ-1 and especially CAZ-6. Except for CAZ-1, which was mediated by a 150-kilobase (kb) plasmid (pCFF14), the other ceftazidimases were mediated by plasmids of 85 kb with EcoRI digestion patterns similar to that of pCFF04 encoding CTX-1 beta-lactamase. A TEM probe hybridized with a 19-kb EcoRI fragment of all these closely related plasmids.

Conjugation, Genetic↗
PubMed1989

Structural features related to hydrolytic activity against ceftazidime of plasmid-mediated SHV-type CAZ-5 beta-lactamase.

Tryptic peptides of the novel ceftazidimase CAZ-5 were sequenced by manual Edman degradation and aligned according to strong homology (more than 98%) with SHV-1 and SHV-2 beta-lactamase sequences. CAZ-5 differed from SHV-1 by five amino acid substitutions. Unusually high activity of CAZ-5 towards ceftazidime was imputed to substitution of a Lys for a Glu at position 214 of the mature protein.

Amino Acid Sequence↗
PubMed1989

Characterization of a plasmid coding for resistance to broad-spectrum cephalosporins in Salmonella typhimurium.

Five strains of Salmonella typhimurium isolated from faeces of infants hospitalized at Trousseau Hospital in Paris have been found to be resistant to third-generation cephalosporins. This resistance is by a transferable plasmid-mediated mechanism. The beta-lactamase gene which encodes for an enzyme similar to SHV-2 has been cloned into plasmid pBR322 and expressed in Escherichia coli RR1.

Cefotaxime↗
PubMed1989

The kinetics of CAZ-5, a novel SHV-related plasmid-mediated beta-lactamase with enhanced hydrolytic activity against ceftazidime.

The kinetic constants for "CAZ-5", a novel plasmid-mediated beta-lactamase with noticeable activity against third-generation cephalosporins and particularly ceftazidime have been determined. Two closely-related plasmid-mediated beta-lactamases have also been studied: SHV-2 and PIT-2 (also known as SHV-1). These enzymes were synthesized constitutively; they were highly sensitive to the action of the inhibitors clavulanic acid and sulbactam and they lacked activity against the cephamycins and imipenem. PIT-2/SHV-1 had poor hydrolytic activity against the third-generation cephalosporins, SHV-2 was markedly active against cefotaxime and related compounds, whereas the new enzyme, which was also active against these cephalosporins, had a noticeably greater activity against ceftazidime. Aztreonam was slowly hydrolysed by CAZ-5 beta-lactamase, but demonstrated an unusually high affinity for this enzyme.

Ceftazidime↗
PubMed1988

[Behavior of ceftazidime in regard to different classes of beta-lactamases. The situation in 1988].

Following Ambler's observations, B-lactamases can be divided in four classes, probably derived from a very small number of ancestral genes. Class A includes the TEM-type beta-lactamases (TEM-1, TEM-2), PIT-2/SHV-1 and others which do not hydrolyse ceftazidime and other third-generation cephalosporins. The new plasmid-mediated beta-lactamases markedly active against third-generation cephalosporins also belong to class A and the primary structures of few of them are known. All the class A beta-lactamases are highly susceptible to the action of beta-lactamase inhibitors: clavulanic acid, sulbactam, YTR-830, and are devoid of any hydrolytic properties for cephamycins and imipenem. Third-generation cephalosporins are slowly hydrolyzed by the class C beta-lactamases: the inducible cephalosporinases. Thus only organisms which produce derepressed cephalosporinases are resistant to third-generation cephalosporins, but individual variations are known.

Ceftazidime↗
PubMed1988

Single amino acid substitution between SHV-1 beta-lactamase and cefotaxime-hydrolyzing SHV-2 enzyme.

SHV-2 beta-lactamase was purified from an overproducing variant of a clinical isolate of Escherichia coli resistant to cefotaxime. Pure protein was digested by trypsin and Lys-C endoproteinase. Proteolytic peptides, isolated by reverse-phase HPLC, were submitted to manual Edman degradation and aligned by homology with the sequence of SHV-1 beta-lactamase. A putative amino acid sequence was deduced. Structural comparison revealed that SHV-2 differed from SHV-1 by only one amino acid, Gly----Ser, at position 213 of the mature protein.

Amino Acid Sequence↗
PubMed1988

Complete amino acid sequence of p453-plasmid-mediated PIT-2 beta-lactamase (SHV-1).

The complete amino acid sequence of the p453-plasmid-mediated PIT-2 beta-lactamase (SHV-1) was determined. The protein contains 265 residues. Peptides resulting from digestions with trypsin, Staphylococcus aureus V8 proteinase, chymotrypsin and Lys-C proteinase and cleavage with CNBr were separated and purified by using reverse-phase h.p.l.c. The amino acid sequence of each peptide was manually determined with the dimethylaminoazobenzene isothiocyanate/phenyl isothiocyanate double-coupling method. The primary structure of PIT-2 beta-lactamase was compared with those of two closely related enzymes, namely TEM-1 beta-lactamase and the beta-lactamase of Klebsiella pneumoniae strain LEN-1. The PIT-2 beta-lactamase amino acid sequence was strongly retained, with respectively 68% and 88% homology. Thus PIT-2 enzyme could represent an evolutionary step between a chromosomally encoded beta-lactamase and the plasmid-mediated TEM beta-lactamases.

Amino Acid Sequence↗
PubMed1988

N-aryl 3-halogenated azetidin-2-ones and benzocarbacephems, inhibitors of beta-lactamases.

N-(3-Carboxy-6-methylphenyl)-3-fluoroazetidin-2-one and a series of related N-aryl-3-halo- and -3,3-dihaloazetidinones 3, in which the halo substituent is a fluorine or a bromine atom, were prepared by using the Wasserman procedure of cyclization of beta-bromopropionamides as a key step. Their affinities for the TEM-1 beta-lactamase were determined and compared with those of a series of tricyclic azetidinones, the benzocarbacephems 2, and known beta-lactamase inhibitors. The beta-lactams 2 and 3 behave as competitive inhibitors and not as substrates of the enzyme; neither halogen substitution (series 3) nor ring strain (series 2) induces enzymatic hydrolysis.

Azetidines↗