Purification and properties of a constitutive beta-lactamase from Pseudomonas aeruginosa strain Dalgleish

Molecular dynamics of class A β-lactamases-effects of substrate binding

The effects of substrate binding on class A β-lactamase dynamics were studied using molecular dynamics simulations of two model enzymes; 40 100-ns trajectories of the free and substrate-bound forms of TEM-1 (with benzylpenicillin) and PSE-4 (with carbenicillin) were recorded (totaling 4.0 μs). Substrates were parameterized with the CHARMM General Force Field. In both enzymes, the Ω loop exhibits a marked flexibility increase upon substrate binding, supporting the hypothesis of substrate gating. However, specific interactions that are formed or broken in the Ω loop upon binding differ between the two enzymes: dynamics are conserved, but not specific interactions. Substrate binding also has a global structuring effect on TEM-1, but not on PSE-4. Changes in TEM-1's normal modes show long-range effects of substrate binding on enzyme dynamics. Hydrogen bonds observed in the active site are mostly preserved upon substrate binding, and new, transient interactions are also formed. Agreement between NMR relaxation parameters and our theoretical results highlights the dynamic duality of class A β-lactamases: enzymes that are highly structured on the ps-ns timescale, with important flexibility on the μs-ms timescale in regions such as the Ω loop.

Cephalosporins determination with a novel microbial biosensor based on permeabilized Pseudomonas aeruginosa whole cells

A new potentiometric microbial biosensor based on Pseudomonas aeruginosa was developed in this study for detecting the cephalosporin group of antibiotics. Preliminary results with the biosensor indicated that P. aeruginosa cells, when treated with lysozyme, showed more efficiency in detecting cephalosporin C in a wide concentration range of 0.1-11 mM with high sensitivity compared to the normal cells. Optimization of the three important biosensor design parameters permeabilized cell contents, quantities of gelatin, and glutaraldehyde resulted in high performance of the biosensor. The optimized values of the above parameters were cell contents 2.5 mg/cm(2), gelatin 8.5 mg/cm(2), and 0.25% glutaraldehyde. The assay conditions, namely phosphate buffer pH, ionic strength, and temperature, were optimized for best performance of the biosensor. The specificity test of the biosensor towards detecting different beta-lactam antibiotics showed good response only for the cephalosporins. The operational and storage stability in detecting cephalosporin C indicated very good potential of the biosensor in detecting cephalosporins with high accuracy.

Characterization of poxB, a chromosomal-encoded Pseudomonas aeruginosa oxacillinase

Pseudomonas aeruginosa is the major pathogen associated with morbidity and mortality of patients with cystic fibrosis. One of the reasons for the failure of beta-lactam antibiotic regimens appears to be mediated by de-regulation of the ampC gene, encoding the chromosomal Ambler's Class C beta-lactamase. Currently, the AmpC is the only known chromosomal beta-lactamase whose expression is regulated by a transcriptional regulator, AmpR. We generated an ampC mutation in the prototypic P. aeruginosa strain PAO1. The mutation in ampC did not abolish the beta-lactamase activity entirely suggesting the expression of yet another unreported beta-lactamase. Our genomic analysis revealed the presence of an open reading frame encoding a protein with high homology to the Class D beta-lactamases, commonly known as oxacillinases. The gene was named poxB for Pseudomonas oxacillinase. Cloning and expression of poxB in Escherichia coli conferred beta-lactam resistance to the host. We detected the presence of poxB both in clinical and environmental isolates. Our studies show that P. aeruginosa possesses two beta-lactamases, AmpC and PoxB, which contribute to its resistance against a wide spectrum of beta-lactam antibiotics.

Structure of CARB-4 and AER-1 carbenicillin-hydrolyzing beta-lactamases

We determined the nucleotide sequences of blaCARB-4 encoding CARB-4 and deduced a polypeptide of 288 amino acids. The gene was characterized as a variant of group 2c carbenicillin-hydrolyzing beta-lactamases such as PSE-4, PSE-1, and CARB-3. The level of DNA homology between the bla genes for these beta-lactamases varied from 98.7 to 99.9%, while that between these genes and blaCARB-4 encoding CARB-4 was 86.3%. The blaCARB-4 gene was acquired from some other source because it has a G+C content of 39.1%, compared to a G+C content of 67% for typical Pseudomonas aeruginosa genes. DNA sequencing revealed that blaAER-1 shared 60.8% DNA identity with blaPSE-3 encoding PSE-3. The deduced AER-1 beta-lactamase peptide was compared to class A, B, C, and D enzymes and had 57.6% identity with PSE-3, including an STHK tetrad at the active site. For CARB-4 and AER-1, conserved canonical amino acid boxes typical of class A beta-lactamases were identified in a multiple alignment. Analysis of the DNA sequences flanking blaCARB-4 and blaAER-1 confirmed the importance of gene cassettes acquired via integrons in bla gene distribution.

Methods for the Measurement of a Bacterial Enzyme Activity in Cell Lysates and Extracts

The kinetic characteristics and regulation of aspartate carbamoyltransferase activity were studied in lysates and cell extracts of Helicobacter pylori by three diffirent methods. Nuclear magnetic resonance spectroscopy, radioactive tracer analysis, and spectrophotometry were employed in conjunction to identify the properties of the enzyme activity and to validate the results obtained with each assay. NMR spectroscopy was the most direct method to provide proof of ACTase activity; radioactive tracer analysis was the most sensitive technique and a microtitre-based colorimetric assay was the most cost-and time-efficient for large scale analyses. Freeze-thawing was adopted as the preferred method for cell lysis in studying enzyme activity in situ. This study showed the benefits of employing several different complementary methods to investigate bacterial enzyme activity.

Development of test panel of beta-lactamases expressed in a common Escherichia coli host background for evaluation of new beta-lactam antibiotics

A test panel of 35 different beta-lactamases expressed in a common Escherichia coli host was created to compare the effect that each beta-lactamase had on susceptibility to various beta-lactam antibiotics. A comparison of the MICs obtained with this panel generally reflected differences in the substrate profiles of the various beta-lactamases examined. In addition, several strains of the panel were subjected to selection with porin-specific bacteriophages to obtain mutants lacking either the OmpC or OmpF porin protein. A mutation in either OmpC or OmpF did change the susceptibilities of certain strains expressing beta-lactamase to certain beta-lactam antibiotics. However, the loss of a single porin did not predictably alter susceptibility to any given beta-lactam drug. This panel of strains producing various beta-lactamases was found to be a useful tool for comparing the effects of different beta-lactamases and outer membrane permeability upon susceptibility to beta-lactam drugs.

Comparative activities of clavulanic acid, sulbactam, and tazobactam against clinically important beta-lactamases

Clavulanic acid, sulbactam, and tazobactam are inhibitors of a variety of plasmid-mediated beta-lactamases. However, inhibition data for these three inhibitors with a wide range of different plasmid-mediated beta-lactamases have not yet been compared under the same experimental conditions. A number of groups have inferred that clavulanic acid inhibits extended-spectrum TEM and SHV beta-lactamases, but inhibition data have rarely been published. In this study, the 50% inhibitory concentrations of these three beta-lactamase inhibitors for 35 plasmid-mediated beta-lactamases have been determined. Of these 35 beta-lactamases, 20 were extended-spectrum TEM- or SHV-derived beta-lactamases. The other 15 enzymes were conventional-spectrum beta-lactamases such as TEM-1 and SHV-1. Clavulanic acid was a more potent inhibitor than sulbactam for 32 of the 35 plasmid-mediated beta-lactamases tested. In particular, clavulanic acid was 60 and 580 times more potent than sulbactam against TEM-1 and SHV-1, respectively, currently the two most clinically prevalent gram-negative plasmid-mediated beta-lactamases. Statistical analysis of the data of the 50% inhibitory concentrations showed that clavulanic acid was 20 times more active overall than sulbactam against the conventional-spectrum enzymes. In addition, clavulanic acid was 14 times more potent than sulbactam at inhibiting the extended-spectrum enzymes. Tazobactam also showed significantly greater activity than sulbactam against the two groups of beta-lactamases. There were no significant differences between the overall activities of tazobactam and clavulanic acid against the extended-spectrum TEM and SHV enzymes and conventional-spectrum enzymes, although differences in their inhibition profiles were observed.

Sequence and molecular characterization of the ROB-1 beta-lactamase gene from Pasteurella haemolytica

The ROB-1 beta-lactamase-encoding plasmids from eight Pasteurella and two Haemophilus strains were compared by restriction endonuclease and hybridization analyses. Two types of ROB-1-encoding plasmids, which differed in size, were detected. One (4.1 kb) was found only in Pasteurella strains. The other (4.4 kb) was found in both Haemophilus influenzae and in one of the eight Pasteurella strains examined. These two plasmids shared multiple homologous fragments, suggesting that one was derived from the other. The ROB-1-encoding gene from Pasteurella haemolytica LNPB 51 was cloned and sequenced. An open reading frame of 915 nucleotides was found; it encoded a 305-amino-acid protein. Analysis of this amino acid sequence confirmed that the enzyme was found; it encoded a 305-amino-acid protein. Analysis of this amino acid sequence confirmed that the enzyme is a class A beta-lactamase. It had 32 to 48% homology with other class A enzymes and exhibited several common features of the gram-positive beta-lactamases. The ROB-1 mature protein, however, contained only one cysteine residue at position 123. These results suggest that ROB-1 is a link between beta-lactamases of gram-negative and gram-positive bacteria. An internal 230-bp DraI fragment from ROB-1 hybridized only with plasmid DNA from ROB-1-producing strains. This specific probe could be useful in epidemiological studies.

OHIO-1 beta-lactamase is part of the SHV-1 family

The OHIO-1 beta-lactamase gene was subcloned in a 1.16-kilobase TaqI fragment in the 2.4-kilobase chimeric plasmid pSK04. After directional subcloning into M13, the DNA sequence of this fragment was determined. The results showed an open reading frame of 858 base pairs (bp) encoding a protein of 286 amino acids. The structural gene showed 95, 87, and 60% DNA sequence identity with SHV-1, LEN-1, and TEM-1, respectively, and 93, 85, and 62% predicted amino acid sequence identity, respectively. The 87 bp upstream of the OHIO-1 structural gene had 96% identity with the upstream flanking sequence of SHV-1, including the -35 and -10 consensus sequences and the putative ribosomal binding site. A 223-bp DNA probe derived from a PstI-HaeII fragment in the C-terminal sequence of OHIO-1 had predicted 96, 88, and 61% sequence identity with SHV-1, LEN-1, and TEM-1, respectively. This probe hybridized to SHV-1 and poorly to LEN-1, but not to TEM-1 or a variety of other plasmid-mediated beta-lactamase genes, under stringent conditions. Screening of plasmid DNA derived from 40 ampicillin-resistant clinical isolates by Southern hybridization with the 223-bp probe uncovered no strains encoding OHIO-1. Isoelectric focusing of the same collection did identify two strains producing enzymes resembling SHV-1, however. We have also performed a kinetic comparison of OHIO-1, SHV-1, and TEM-1. OHIO-1 and SHV-1 were indistinguishable from each other but could be distinguished from TEM-1. These data clearly place OHIO-1 within the SHV-1 family of beta-lactamases.

Antibiotic resistance in the tropics. 1. The genetics of bacterial ampicillin resistance in tropical areas

Ampicillin and its derivatives are the most widely used beta-lactam antibiotics throughout the world. Ampicillin resistance in Gram-negative bacteria is usually manifested by plasmid-encoded beta-lactamases, which hydrolyse the beta-lactam ring of the antibiotic. There are at least 30 different plasmid-encoded beta-lactamases but almost all of them are found very infrequently. The one exception is the TEM-1 beta-lactamase which is found wherever transferable ampicillin resistance emerges and accounts for over 50% of all plasmid encoded ampicillin resistance. In India, the incidence of ampicillin resistance is high (82%) and, amongst Escherichia coli, a significant proportion of the plasmid-encoded beta-lactamases are different from those found in the United Kingdom. Although many Gram-negative species are able to accept the TEM-1 beta-lactamase, certain species have a pre-disposition to their own plasmid beta-lactamase types.

Novel plasmid-mediated beta-lactamase in members of the family Enterobacteriaceae from Ohio

Epidemiologic studies of plasmid-mediated resistance at the Cleveland Veterans Administration Medical Center revealed that related plasmids had disseminated among members of the family Enterobacteriaceae. We studied the beta-lactamases encoded by these plasmids in Escherichia coli C600 transformants or transconjugants. Substrate and inhibition profiles of the enzymes determined by two of these plasmids suggested an activity resembling TEM-1; however, isoelectric focusing revealed a pI of 7.0. These two plasmids were originally found in a Serratia marcescens (pDS076) and an Enterobacter cloacae (pDS075) strain isolated from the same sink in the medical intensive care unit and later, in an Enterobacter cloacae (pDS142 identical to pDS076) isolate colonizing a patient in the same unit. The plasmids also carried the aminoglycoside resistance determinant, 2"-aminoglycoside nucleotidyl transferase. A 2-kilobase AvaI restriction endonuclease digestion fragment of pSD075 known to carry the beta-lactamase determinant was used as a molecular probe. This probe did not recognize sequences of any plasmid-mediated beta-lactamase tested including the recently described determinants ROB-1, TLE-1, and OXA-4-7. A TEM-1 probe derived from the 0.7-kilobase PstI-EcoRI fragment of pBR322 failed to recognize the new beta-lactamase gene. Four additional Enterobacter cloacae and two Enterobacter aerogenes strains isolated in Columbus, Ohio, have been shown to produce a pI 7.0 beta-lactamase and to carry plasmids recognized by the 2-kilobase probe. These data suggest dissemination of a novel plasmid-mediated beta-lactamase among members of the family Enterobacteriaceae in Ohio and demonstrate the development and utility of a molecular probe for the new determinant. We suggest that the novel beta-lactamase be named OHIO-1.

Genetic and biochemical properties of AER-1, a novel carbenicillin-hydrolyzing beta-lactamase from Aeromonas hydrophila

A novel carbenicillin-hydrolyzing beta-lactamase has been discovered in a blood isolate of Aeromonas hydrophila. The enzyme resembles plasmid-determined carbenicillinases in substrate profile but differs in isoelectric point (pI 5.9) and molecular weight (22,000) and has been termed AER-1. No evidence for a plasmid location could be obtained in A. hydrophila, but the AER-1 gene and resistance to chloramphenicol, streptomycin, and sulfonamide could be transferred by mobilization with IncP plasmids to Escherichia coli, where the gene cluster inserted at a unique chromosomal site. The linked resistances are similar to those found on multiresistance beta-lactamase transposons, but since insertion of the A. hydrophila gene cluster was site specific and recA+ dependent, the cluster is not a functional transposon.

beta-Lactamase inhibitors

In summary, Table XVI shows the inhibition profiles of representative beta-lactamases from each major class of Richmond and Sykes. Either resistance (R) or sensitivity (S) is given as a general guide to the type of compounds likely to inhibit each class. Thus the (qualitative) statements regarding the effectiveness of clavulanic acid can be taken to represent those for the penam sulfones and similarly for MM4550 and the other olivanic acids, carpetimycins, PS series, and asparenomycins. This can also be said of cloxacillin and the other aromatic carboxamido penicillins. Compounds are also included which are specifically or particularly inhibitory to certain beta-lactamases.

Comparison of polyacrylamide and agarose gel thin-layer isoelectric focusing for the characterization of beta-lactamases

Plasmid-mediated beta-lactamases from strains of Escherichia coli and Pseudomonas aeruginosa were separated by isoelectric focusing on a 0.8-mm thin-layer agarose gel with a pH gradient of 3.5 to 9.5. Their banding patterns and isoelectric points were compared with those obtained with a 2.0-mm polyacrylamide gel as the support medium. The agarose method produced banding patterns and isoelectric points which corresponded to the polyacrylamide gel data for most samples. Differences were observed for HMS-1 and PSE-1 beta-lactamases. The HMS-1 sample produced two highly resolvable enzyme bands in agarose gels rather than the single faint enzyme band observed on polyacrylamide gels. The PSE-1 sample showed an isoelectric point shift of 0.2 pH unit between polyacrylamide and agarose gel (pI 5.7 and 5.5, respectively). The short focusing time, lack of toxic hazard, and ease of formulation make agarose a practical medium for the characterization of beta-lactamases.

Types of beta-lactamase determined by plasmids in gram-negative bacteria

Two species of beta-lactamase determined by plasmids in enteric bacteria that show some resemblance to TEM enzymes are described. Both are distinct from all other plasmid-mediated beta-lactamases and differ from the TEM beta-lactamases in ability to hydrolyze some substrates, in isoelectric point, in immunological specificity, and in susceptibility to inhibition. One of the enzyme species, mediated by plasmid p453, has been briefly described previously. We have discovered that this beta-lactamase, designated SHV-1, is unique in its response to inhibition by the sulfhydryl group reagent p-chloromercuribenzoate, because the hydrolysis of cephaloridine but not that of benzylpenicillin is affected. This enzyme is found in a variety of plasmid types which were transferred from several bacterial species collected from a wide geographic range. The other enzyme species is novel; only a single plasmid determining this kind of beta-lactamase (designated HMS-1) has been detected.

Properties of the beta-lactamase specified by the Pseudomonas plasmid RPL11

The Pseudomonas plasmid RPL11 specifies a beta-lactamase that has properties distinguishing it from other plasmid-mediated beta-lactamases so far described, although it closely resembles plasmid Rms139 beta-lactamase.

[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.

A specific cephalosporin-binding protein of Citrobacter freundii

1. A cephalosporin-binding protein obtained from a strain of Citrobacter freundii was purified to the extent of a single band in analytical and sodium dodecyl sulfate-containing disc electrophoresis. 2. The molecular weight determined by disc electrophoresis was 53 000. 3. The binding protein did not show any beta-lactamase activity at substrate concentrations examined: 6 mM to 100 muM of penicillins and 12 mM to 100 muM of cephalosporins. 4. In gel filtration, [14C]benzylpenicillin was found not to bind to the binding protein. 5. In fluorescence titration, all cephalosporins tested quenched the fluorescence. Association constants of cephalosporins were in the range of 0.8-12-103 M-1, and one binding site was calculated for all cephalosporins tested.