Frequency of inhibitor-resistant TEM beta-lactamases in Escherichia coli isolates from urinary tract infections in France

Over a six-month period in 1993, 2972 non-duplicated isolates of Escherichia coli causing urinary tract infections were collected in a French teaching hospital (n = 785) and in three private laboratories (n = 2187). The resistance rate to amoxycillin-clavulanate combination (MIC > 16 mg/l) was 25.0% in the hospital isolates and 10.0% in the community isolates. Respectively, 27.5% and 45.0% of hospital and community isolates resistant to amoxycillin-clavulanate exhibited an unusual beta-lactam resistance pattern, suggesting inhibitor-resistant TEM (IRT) beta-lactamase production. These isolates were highly resistant to amoxycillin-clavulanate (MIC90 > 1024 mg/L), but were susceptible to cephalosporins (MIC < 32 mg/L). Enzyme extracts of these IRT-producing strains focused at pI 5.2 (n = 100) or 5.4 (n = 53). DNA-DNA hybridization confirmed that the beta-lactamases involved in this resistance mechanism were TEM-1 derived and contained variations in the altered positions described in IRT enzymes. This study shows a total frequency of 4.9% of IRT-producing isolates among E. coli isolated from urine specimens.

[Molecular mechanisms of bacterial resistance]

There is a great variety of resistance mechanisms observed in bacteria. Several mechanisms can operate simultaneously against a single antibiotic, and there are no species-specific mechanisms described so far. In many cases, resistance is mediated by mobile genetic elements (plasmids, phages and transposons), spreading among different bacterial genera, carrying in many instances multiresistant determinants. Administration of one type of antimicrobial agent can select resistance to other groups of antimicrobials. In summary, more details are found every day on these molecular processes. All this constitute an important tool for the design of new antimicrobials with broad specificity and higher efficacy in an attempt to control bacterial resistance. More important yet, this knowledge has a necessary implication which translates into a rational and adequate use of antimicrobial agents in the fight against bacterial infections.

A sensitive ELISA for 6 beta-hydroxycortisol in urine using enzyme penicillinase (beta-lactamase)

A sensitive and specific, enzyme labelled immunosorbent assay (ELISA) for 6 beta-hydroxycortisol in diluted urine using penicillinase was developed. 6 beta-Hydroxycortisol-21-hemisuccinate was conjugated with enzyme penicillinase. Antibody immobilized on a polyvinylchloride ELISA plate (Dynatech) was used for separation of bound from free ligand. The sensitivity of the assay was between 2.0-3.0 pg per well and recovery of 6 beta-hydroxycortisol from urine ranged between 85.0-108.0%. The assay is simple, rapid and precise.

[Extended spectrum beta-lactamases]

At least 30 extended-spectrum beta-lactamases (ESB) have emerged responsible for resistance to indigestible beta-lactams (C3G) since their discovery in West Germany in 1983. Most of them are produced by enterobacteria and essentially K. pneumoniae which appeared susceptible to oxyimino-beta-lactams. A double-disk test was useful to detect such nosocomial isolates of enterobacteria (urines, blood, wound, sputum cultures) mostly recovered from patients in intensive care units. These have spread through hospital and outbreaks were described. Because plasmid-encoded this resistance mechanism was spreading among enterobacteria with other resistance markers (e.g. netilmicin, amikacin). It seems highly likely that the use of newer antibiotics favors the appearance of ESB obtained by selection of mutated genes coding for penicillinases (TEM, SHV). Treatment including a beta-lactam is still possible because of the stability of some beta-lactams e.g. cefamycins, carbapenems and the sensitivity to beta-lactam inhibitors. Digestive selective decontamination may overcome outbreak.

[Acute pharyngo-tonsillitis. Penicillin, yes or no?]

Acute tonsillitis and acute pharyngitis show a high incidence in the healthy population. Recent microbiological studies have demonstrated changes in the frequency with which different microorganisms promote such infections. This fac, together with the variations in sensibility or resistance of germs to the diverse therapeutic agents, have led to the conclusion that penicillin must not be considered as the solo drug of choice in these infections.

Determination of a new cephalosporin, SCE-2787, in serum and urine by high-performance liquid chromatography

A high-performance liquid chromatographic method for the determination of a new-broad spectrum cephalosporin (I, SCE-2787) has been developed. The analyte was extracted from serum by precipitation of serum proteins with acetonitrile. Acetonitrile was extracted from the protein-free supernatant by dichloromethane. Urine was simply diluted with mobile phase. Separation was performed by ion-pair chromatography on a reversed-phase column (Nucleosil 5C18; 125 mm x 4.0 mm I.D.; 5 microns average particle size). The guard column was Perisorb RP18 (30 mm x 4.0 mm I.D.; 30-40 microns particle size). The mobile phase was acetonitrile-buffer solution containing 15 mM heptanesulphonic acid (pH 3.2) (4.5:95.5, v/v). Detection was performed at 235 nm with a diode-array detector, which also served to record ultraviolet spectra. The assay was sensitive, precise, accurate and fast. Specificity was controlled by on-line recording the ultraviolet spectrum of I and also by enzymic degradation with beta-lactamase. No interferences were observed during the analysis of serum and urine of healthy volunteers in pharmacokinetic studies.

[Multifactorial analysis of the phenotypes for beta-lactams of 1044 Escherichia coli strains]

1,044 E. coli strains were randomly collected by the beginning of 1992. Their susceptibility for seven beta-lactam antibiotics: amoxycillin, augmentin, ticarcillin, claventin, cephalothin, cefoxitin and cefotaxime, was studied routinely by the agar diffusion method. The datas were analyzed by the CERIB multifactorial analysis package which yields to homogeneous populations. This analysis showed four well defined populations: 1) 588 strains (56.4%) susceptible to all antibiotics; 2) 410 strains (39.3%) present a penicillinase phenotype; 3) 11 strains (1.05%) are cephalosporinase producer; 4) 7 strains (0.67%) were identified as producing an extended-spectrum beta-lactamase. The remaining strains: 28 (2.68%) had a reduced susceptibility to all antibiotics, which suggests the combination of few resistance mechanisms or other hypothesis.

Detection of penicillin tolerance in Streptococcus pyogenes

Three traditional assays were used to determine the minimal bactericidal concentration (MBC) and minimal inhibitory concentration (MIC) for Streptococcus pyogenes (group A streptococci) in two phases of growth and the time taken to kill the organisms. Three other methods were used for the determination of penicillin tolerance: a cell-lysis assay, the beta-lactamase disk method and the replication method. Twenty strains, comprising penicillin-tolerant clinical isolates and two laboratory mutants, were used to evaluate the six tests. Results indicated that two groups of S. pyogenes can be distinguished--four highly tolerant and three moderately tolerant strains. The moderately tolerant strains were not recognised when rapidly growing instead of stationary cultures were used for the MBC and MIC determinations. The MBC/MIC ratio for tolerant strains was > 100. Tolerance percentage ranged from 0.30 to 1.07 and 0.29 to 3.96 for cultures in the mid-logarithmic and stationary phases of growth, respectively. The cell-lysis assay, the beta-lactamase disk method and the replication method may be used to screen for tolerance. Detection of high or moderate tolerance by determining the MBC/MIC ratio for mid-logarithmic or stationary cultures is recommended.

Cefoxitin-induced antibiotic resistance in Enterobacter species in the community hospital

The aim of this study was to determine whether beta-lactamases could be induced by cefoxitin in the community hospital, since this problem of antibiotic resistance has been shown to exist at the tertiary care level. One hundred sixty-six Enterobacter species isolated from patients in two community hospitals in Dayton, Ohio, were tested for cefoxitin induction of beta-lactamase production by a disk-approximation method. Piperacillin and cefoxitin disks were placed in approximation to each other on Mueller-Hinton plates inoculated with Enterobacter species with appropriate controls. Three Enterobacter strains (1.8%) showed truncation of the zone of inhibition (indicating beta-lactamase induction) with sensitivity to both cefoxitin and piperacillin. However, 84 strains (50.6%) showed truncation around the piperacillin disk with resistance to cefoxitin. One hundred fifty (90.0%) strains showed resistance to cefoxitin. These data indicate that cefoxitin induction of beta-lactamases in Enterobacter species is indeed a potential problem in incurring antibiotic resistance in the community hospital.

Ten-year review of otitis media pathogens

Data collected from 1980 to 1989 by investigators at the Pittsburgh Otitis Media Research Center were examined to detect changes over time in the prevalence of bacteria isolated from middle ear effusions in patients with otitis media. The organisms isolated most commonly from the 7396 effusions cultured at the center were Streptococcus pneumoniae and Haemophilus influenzae. S. pneumoniae predominated in the subgroup of patients with acute otitis media, whereas H. influenzae was isolated most frequently from patients with otitis media with effusion. The most notable changes to occur during the 10-year period were a statistically significant increase in the prevalence of S. pneumoniae in patients with acute otitis media and a progressive rise in the percentage of beta-lactamase-producing strains of H. influenzae and Moraxella (Branhamella) catarrhalis. The latter finding suggests the need for therapeutic alternatives to amoxicillin, which is not active against beta-lactamase-producing organisms, when these organisms are suspected or cultured from the middle ear.

Antibacterial activity of the investigational oral and parenteral cephalosporin BK-218

BK-218 is a novel cephalosporin with a dual route of administration and spectrum of activity most similar to that of second-generation cephalosporins. BK-218 was active against Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis but strains resistant to penicillins had higher MICs. BK-218 had greater activity (8-fold) than cefuroxime or cefaclor against oxacillin-susceptible Staphylococcus spp. Moderate BK-218 activity was observed against Neisseria gonorrhoeae and commonly isolated Enterobacteriaceae such as Escherichia coli (MIC90, 1 mg/l), Klebsiella spp. (MIC90, 2 mg/l), and Proteus mirabilis (MIC90, 2 mg/l). The following organisms were generally BK-218-resistant (MIC90, greater than 16 mg/l): Bacteroides fragilis, Pseudomonas spp., Acinetobacter spp., Xanthomonas maltophilia, Citrobacter spp., Enterobacter spp., indole-positive Proteus, Serratia spp., enterococci and oxacillin-resistant staphylococci.

Use of multiple markers for investigation of an epidemic of Shigella sonnei infections in Monroe County, New York

Antibiotic susceptibility patterns, plasmid profiles, and endonuclease restriction analysis of plasmid DNA were used in the investigation of an epidemic of Shigella sonnei infections in Monroe County, New York, in 1988 and 1989. The epidemic peaked during the winter, included the simultaneous transmission of the disease from person to person and from common food sources, and especially affected inhabitants of the poor, inner-city neighborhoods, young children of both sexes, and women. Resistance to ampicillin, tetracycline, or trimethoprim-sulfamethoxazole, encoded in a 70-MDa plasmid, was found in most of the examined isolates. Unexpectedly, isolates from patients involved in a food-borne outbreak exhibited three different antibiotic susceptibility patterns, suggesting deletion of antibiotic resistance determinants in some strains. Antibiograms clearly separated food-borne outbreak-related and non-foodborne outbreak-related strains, distinguished more strains than did the plasmid profiles, and were useful in tracing the dissemination of individual isolates in the community. Restriction endonuclease analysis substantially increased the discriminatory value of plasmid profiles and validated the antibiogram results. The present study illustrates the complexity of epidemics of S. sonnei infections and shows the value of combining different biological markers in the investigation.

A simple ELISA procedure for HIV-1 based on the enzyme beta-lactamase

The enzyme beta-lactamase (penicillin-amido-beta-lactam-hydrolase, EC 3.5.2.6.) has been shown to be suitable for use in ELISA procedures. The assay proposed requires a conjugate containing a beta-lactam-hydrolase as the enzymatic component, penicillin or one of its derivatives as substrate and an iodic complex (an iodine-starch or an iodine-polyvinylic alcohol complex) as the chromogenic component. Binding of conjugate molecules results in the transition of the iodic complex from dark blue to colourless. The transition is readily visualized without the aid of an EIA reader. The decolorization occurs specifically giving a clear-cut yes/no decision without a cut-off value. The rate of the colour transition strongly depends on the amount of bound conjugate. beta-lactamase-based ELISA techniques are of potential use in the immunological diagnosis of some virus diseases. The sensitivity and specificity of the assay were assessed on a panel of 670 negative and 141 positive HIV-1 sera, giving values of 100% and 99.85%, respectively.

Identification and DNA sequence of a new Bacteroides fragilis insertion sequence-like element

A new Bacteroides fragilis insertion sequence (IS)-like element has been identified, cloned, and sequenced. The element is 1598 base pairs in length. It is flanked by a 15-base pair imperfect inverted repeat and contains a large open reading frame which could encode a 430 amino acid protein. There is an 8-base pair duplication of genomic DNA sequences at the site of integration. One copy of the IS-like element is integrated within the 5' upstream sequence of the metallo-beta-lactamase gene ccrA, cloned from B. fragilis TAL3636. The IS-like element is integrated 19 bp upstream of the predicted initiation codon and, therefore, probably provides the transcriptional start signals for the CcrA gene.

Remarks on the screening of antibiotics for antibacterial activity

The general principles of screening antibiotics for antimicrobial activity are similar to those for screening for other pharmacological effects. The system should be adapted to the specific character of the test substance and the objectives of the program. In the screening of beta-lactams, standard tests, such as determination of the MICs, effects of inoculum size or activity against systemic infection in mice, should be supplemented by less conventional studies on for instance activity against dormant bacteria or, in the case of penems or carbapenems, stability in the presence of kidney and lung dehydropeptidases.

TnA transposons can be introduced and maintained in Neisseria gonorrhoeae

In Neisseria gonorrhoeae, all penicillinase-specifying plasmids isolated so far share homology with each other and carry a 60% deleted sequence of TnA. Plasmid pHD131, an element isolated from Haemophilus ducreyi and carrying an intact copy of the ampicillin resistance transposable element, was introduced from Escherichia coli into N. gonorrhoeae by both transformation and conjugative mobilization. Plasmids were recovered with no detectable deletion. After their transfer back into E. coli, transposition assays onto phage-lambda DNA demonstrated that the TnA elements were still functional. Plasmid pHD131 could be stably maintained in N. gonorrhoeae with or without the presence of penicillin. These results support the hypothesis that the absence in N. gonorrhoeae of plasmids carrying entire and functional TnA transposons cannot be ascribed to incompatibility between the genetic element and the host, but rather to a barrier to introduction of foreign DNA into gonococcus.

Antimicrobial activity and stability to beta-lactamase of BMY-28271, a new oral cephalosporin ester

BMY-28271, the acetoxyethyl ester of BMY-28232, 7-[(Z)-2-(2-aminothiazol-4-yl)-2-hydroxyiminoacetamido]-3(Z) -propen-1-yl-3- cephem-4-carboxylic acid, is a new oral cephalosporin. BMY-28232 has a widely expanded spectrum with high activity against gram-positive and gram-negative bacteria. BMY-28232 is far more active than cefixime or cefteram against Staphylococcus aureus and Staphylococcus epidermidis. Against gram-negative bacteria, the activity of BMY-28232 was comparable to or somewhat weaker than that of cefixime or cefteram. BMY-28232 was a poor substrate for various beta-lactamases. Orally administered BMY-28271 had a good therapeutic effect on systemic infections with S. aureus and some gram-negative bacteria in mice. Oral BMY-28271 was efficacious against S. aureus Smith infection: the efficacy of BMY-28271 was 80 to 90 times higher than that of cefixime or cefteram.

Failure of cephalosporins to prevent Staphylococcus aureus surgical wound infections

Approximately 35,000 Staphylococcus aureus surgical wound infections occur annually in the United States. To investigate why S aureus causes infection despite the perioperative administration of cephalosporins, we compared 35 methicillin-susceptible isolates recovered from deep wound infections that complicated cefazolin prophylaxis (18 of 1650 patients) and cefamandole prophylaxis (17 of 3702 patients) with 64 colonizing isolates from presurgical patients. Compared with both colonizing and cefamandole-associated isolates, S aureus isolates from cefazolin-associated infections were more resistant to cefazolin by specialized assays. Staphylococcus aureus isolates that produced the A and C variants of staphylococcal beta-lactamase were associated with infections following cefazolin and cefamandole prophylaxis, respectively. These isolates hydrolyze the respective cephalosporins rapidly, suggesting that staphylococcal survival after perioperative prophylaxis may be mediated by in vivo degradation of the prophylactically administered cephalosporin. These data indicate that some S aureus wound infections occur because of deficiencies in antimicrobial effectiveness that are not detectable by routine susceptibility tests. This finding has important implications for the therapy and prevention of S aureus infection.

[In vitro effect of cefixime against 200 strains of Branhamella catarrhalis. Comparison with cefotaxime]

The in vitro activity of cefixime was tested against 200 strains of Branhamella catarrhalis. Of these strains, 146 had been collected during 1987 from 15 different "Centres hospitaliers généraux", through a multicenter collaborative investigation organized by the "Collège de Bactériologie-Virologie-Hygiène des hôpitaux généraux". The remaining 54 strains were isolated at the "Centre hospitalier", of Aix-en-Provence. The strains originated from: bronchopulmonary collections: 80.2 per cent, sinusitis: 5.6 per cent, conjunctivitis: 4.6 per cent, otitis: 3.5 per cent, blood cultures: 0.5 per cent, miscellaneous: 5.6 per cent. Seventy-three per cent of the strains produced beta-lactamases. MIC determination was performed according to the agar dilution procedure on non-enriched Mueller-Hinton agar (30 hours incubation at 37 degrees C without CO2). The inoculum was 10(5) CFU per spot. Non beta-lactamase producing strains displayed the following MIC 50 and MIC 90 values (mg/l): amoxicillin: 0.03 - 0.125; cefotaxime: 0.06 - 1; cefixime: 0.06 - 0.5. Beta-lactamase producing strains were generally more resistant: amoxicillin: 32 - 128; cefotaxime: 1 - 2, and cefixime: 0.5 - 1.

[In vitro effect of cefixime against Haemophilus influenzae]

Cefixime activity has been determined against Haemophilus influenzae strains producing or not beta-lactamase, or resistant to ampicillin by non-enzymatic mechanism. All strains are inhibited by a concentration of 1 mg/l of cefixime independently of beta-lactamase secretion. Ampicillin-resistant non beta-lactamase producing strains are inhibited by concentrations of 0.12 - 1 mg/l. MIC50 and MIC90 were, respectively, 0.06 and 0.12 mg/l for ampicillin-susceptible strains and 0.12 and 0.12 mg/l for ampicillin-resistant strains. The activity of cefixime against Haemophilus influenzae was superior to that of other orally administered antibiotics tested in this study: amoxicillin, amoxicillin-clavulanic acid, cefaclor and cefuroxime.

In vitro antibacterial activity and beta-lactamase stability of the new carbapenem SM-7338

The in vitro activity of the new carbapenem SM-7338 was tested in comparison with imipenem, ceftazidime, cefotaxime, flomoxef, cefuzonam and cefmetazole against 2850 clinical bacterial isolates. SM-7338 showed good activity against a broad spectrum of gram-positive and gram-negative bacteria. SM-7338 was very active against gram-negative bacteria, inhibiting all Enterobacteriaceae, except 25% of Serratia marcescens isolates, at a concentration of 0.78 mg/l. SM-7338 inhibited the majority of Pseudomonas spp. at concentrations of less than or equal to 3.13 mg/l, its activity being twofold higher than that of imipenem. However, the activity of SM-7338 against gram-positive cocci was about one-fourth that of imipenem. Against anaerobes, SM-7338 also had the best activity of the beta-lactams tested. The compound was inactive against methicillin-resistant staphylococci, Enterococcus faecium, Xanthomonas maltophilia and Flavobacterium spp., as were the other beta-lactams. SM-7338 was quite stable in the presence of various types of beta-lactamase, but was hydrolyzed by Xanthomonas maltophilia beta-lactamase, as was imipenem. This high degree of stability was responsible for the potent activity of SM-7388 against beta-lactamase-producing species such as Enterobacter cloacae, Citrobacter freundii and Proteus vulgaris. SM-7338 also showed bactericidal activity against clinical isolates at the MIC or at concentrations slightly above the MIC.

[An immunoenzyme method of isolation of foot-and-mouth disease virus by using beta-lactamase conjugate with virus-specific antibodies]

It was shown that in was feasible to use conjugates of virus-specific antibodies and beta-lactamase from Bacillus licheniformis 749/c to identify aphthosa virus antigens. The antigen titers determined by enzyme immunoassay (EIA) using a beta-lactamase conjugate were 5-64 times higher than the analogous indices of the complement fixation test. Unlike EIA, that by using the antibody conjugates with peroxidase or alkaline phosphatase there were observed no "background" responses.

[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.

A general method for site-specific incorporation of unnatural amino acids into proteins

A new method has been developed that makes it possible to site-specifically incorporate unnatural amino acids into proteins. Synthetic amino acids were incorporated into the enzyme beta-lactamase by the use of a chemically acylated suppressor transfer RNA that inserted the amino acid in response to a stop codon substituted for the codon encoding residue of interest. Peptide mapping localized the inserted amino acid to a single peptide, and enough enzyme could be generated for purification to homogeneity. The catalytic properties of several mutants at the conserved Phe66 were characterized. The ability to selectively replace amino acids in a protein with a wide variety of structural and electronic variants should provide a more detailed understanding of protein structure and function.

Location of enzymatic and DNA-binding domains on E. coli protease La

Escherichia coli protease La is an ATP-dependent enzyme that has a DNA-binding site. The locations of the enzymatic and DNA-binding sites are not known. We report that a 75-residue segment at the carboxy-terminus of the protease La is similar to part of Bacillus licheniformis beta-lactamase, a serine enzyme. The comparison score is 8.2 standard deviations higher than that obtained with 10,000 comparisons of randomized sequences of these segments. The probability of obtaining such a score by chance is 1.2 x 10(-16). We also find that a 107-residue segment in the amino-terminus half of protease La is similar to part of the sopB protein, a DNA-binding protein of the plasmid F of E. coli. The comparison score for these segments is 8 standard deviations (P = 6 x 10(-16)). These strong amino acid sequence similarities suggest the locations of the catalytic serine and the DNA-binding domains of protease La.

Chemical modification of the RTEM-1 thiol beta-lactamase by thiol-selective reagents: evidence for activation of the primary nucleophile of the beta-lactamase active site by adjacent functional groups

The RTEM-1 thiol beta-lactamase (Sigal, I.S., Harwood, B.G., Arentzen, R., Proc. Natl. Acad. Sci. U.S.A. 79:7157-7160, 1982) is inactivated by thiol-selective reagents such as iodoacetamide, methyl methanethiosulfonate, and 4,4'-dipyridyldisulfide, which modify the active site thiol group. The pH-rate profiles of these inactivation reactions show that there are two nucleophilic forms of the enzyme, EH2 and EH, both of which, by analogy with the situation with cysteine proteinases, probably contain the active site nucleophile in the thiolate form. The pKa of the active site thiol is therefore shown by the data to be below 4.0. This low pKa is thought to reflect the presence of adjacent functionality which stabilizes the thiolate anion. The low nucleophilicity of the thiolate in both EH2 and EH, with respect to that of cysteine proteinases and model compounds, suggests that the thiolate of the thiol beta-lactamase is stabilized by two hydrogen-bond donors. One of these, of pKa greater than 9.0, is suggested to be the conserved and essential Lys-73 ammonium group, while the identity of the other group, of pKa around 6.7, is less clear, but may be the conserved Glu-166 carboxylic acid. beta-Lactamase activity is associated with the EH2 form, and thus the beta-lactamase active site is proposed to contain one basic or nucleophilic group (the thiolate in the thiol beta-lactamase) and two acidic (hydrogen-bond donor) groups (one of which is likely to be the above-mentioned lysine ammonium group).

In vitro activity of E-1040, a novel cephalosporin with potent activity against Pseudomonas aeruginosa

The in vitro activity of E-1040 [(6R,7R)-3-[(4-carbamoyl-1-quinuclidinio)methyl]-7-[2-(5-amino-1,2 ,4- thiadiazol-3-yl)-(Z)-2-methoxyiminoacetoamido]-8-oxo-5-thia- 1- azabicyclo(4,2,0)oct-2-ene-2-carboxylate], a novel cephalosporin, was compared with that of ceftazidime, cefpirome, cefepime, imipenem, and gentamicin. E-1040 inhibited 50% of members of the family Enterobacteriaceae, Pseudomonas aeruginosa, and Haemophilus and Neisseria species at less than or equal to 0.25 microgram/ml, and the MIC for 90% of strains tested ranged from 0.06 to 2 micrograms/ml. It was two- to fourfold more active than ceftazidime and similar in activity to cefepime and cefpirome. It inhibited Enterobacter, Citrobacter, Serratia, and Morganella species that were resistant to ceftazidime. E-1040 inhibited imipenem-, piperacillin-, aztreonam-, and tobramycin-resistant P. aeruginosa. It was less active against Xanthomonas maltophilia and P. cepacia but inhibited other Pseudomonas species. The activity of E-1040 against staphylococci and hemolytic streptococci was similar to that of ceftazidime, but E-1040 was less active than cefepime and cefpirome. It did not inhibit Bacteroides spp. There was no inoculum effect or medium effect, and MBCs were within a dilution of MICs. Plasmid beta-lactamases TEM-1, TEM-2, TEM-3 (CTX-1), SHV-1, Staphylococcus aureus, PSE, and CARB did not hydrolyze E-1040. Chromosomal beta-lactamases P99 and K-1 did not hydrolyze E-1040; E-1040 had poor affinity for these enzymes, with a Ki of greater than 100 microM.

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.

The active-site-serine penicillin-recognizing enzymes as members of the Streptomyces R61 DD-peptidase family

Homology searches and amino acid alignments, using the Streptomyces R61 DD-peptidase/penicillin-binding protein as reference, have been applied to the beta-lactamases of classes A and C, the Oxa-2 beta-lactamase (considered as the first known member of an additional class D), the low-Mr DD-peptidases/penicillin-binding proteins (protein no. 5 of Escherichia coli and Bacillus subtilis) and penicillin-binding domains of the high-Mr penicillin-binding proteins (PBP1A, PBP1B, PBP2 and PBP3 of E. coli). Though the evolutionary distance may vary considerably, all these penicillin-interactive proteins and domains appear to be members of a single superfamily of active-site-serine enzymes distinct from the classical trypsin or subtilisin families. The amino acid alignments reveal several conserved boxes that consist of strict identities or homologous amino acids. The significance of these boxes is highlighted by the known results of X-ray crystallography, chemical derivatization and site-directed-mutagenesis experiments.

An X-ray-crystallographic study of beta-lactamase II from Bacillus cereus at 0.35 nm resolution

Crystals of beta-lactamase II (EC 3.5.2.6., 'penicillinase') from Bacillus cereus were grown with Cd(II) in place of the natural Zn(II) cofactor and stabilized by cross-linking with glutaraldehyde. Their space group is C2, the cell dimensions are a = 5.44 nm, b = 6.38 nm, c = 7.09 nm and beta = 93.6 degrees, and there is one molecule in the asymmetric unit. Diffraction data were collected from cross-linked crystals of the Cd(II)-enzyme, the apoenzyme and six heavy-atom derivatives. The electron-density map calculated at 0.35 nm resolution reveals the essential Cd(II) ion surrounded by three histidine residues and one cysteine residue. The position of a glutamic acid residue, modification of which destroys activity [Little, Emanuel, Gagnon & Waley (1986) Biochem. J. 233, 465-469], suggests the probable location of the active site of the enzyme. Two minor Cd(II) sites not essential for activity were also located. The structure of the apoenzyme at this resolution appears to differ from that of the Cd(II)-enzyme only in the orientation of two of the histidine residues and the cysteine residue that surround the metal ion.

Inactivation of the thiol RTEM-1 beta-lactamase by 6-beta-bromopenicillanic acid. Identity of the primary active-site nucleophile

The thiol RTEM-1 beta-lactamase [Sigal, Harwood & Arentzen (1982) Proc. Natl. Acad. Sci. U.S.A. 79, 7157-7160] is inactivated by 6-beta-bromopenicillanic acid with formation of a characteristic chromophore, absorbing maximally at 350 nm, which is covalently bound to the enzyme. Model studies suggest that the chromophore is that of a 6-carboxylate thiol ester of 2,3-dihydro-2,2-dimethyl-1,4-thiazine-3,6-dicarboxylate, which can arise by rearrangement of the thiol-penicilloate obtained by thiolysis of the beta-lactam of 6-beta-bromopenicillanate. Loss of activity of the enzyme is also concerted with disappearance of its single (cysteine) thiol group. These results indicate that the thiol group of this enzyme is indeed a nucleophilic catalyst in beta-lactam turnover. The thiol beta-lactamase is also inactivated by clavulanic acid with formation of a chromophore, presumably a 3-aminoacrylate thiol ester, at 308 nm. Both 6-beta-bromopenicillanate and clavulanate are hydrolysed more slowly by the thiol enzyme than by the native serine beta-lactamase, but, probably as a consequence of this, both compounds inactivate the former enzyme more efficiently. Cefoxitin, a poor substrate of the native enzyme, does not appear to interact covalently with the thiol beta-lactamase.

[Determination of antibodies to the AIDS virus and the viral antigen by an immunoenzyme method using peroxidase and beta-lactamase]

The ELISA test using beta-lactamase for the detection of anti-AIDS virus antibodies and virus antigen in serum is described. The properties of this test system are compared with those of the system based on horseradish peroxidase conjugates.

[Immunoenzyme method of determining Pseudomonas aeruginosa exotoxin A by using a conjugate of beta-lactamase with specific antibodies]

Specific antibodies for immunoenzymatic assay of P. aeruginosa exotoxin A were isolated with affinity chromatography on exotoxin A-Sepharose 4B. A conjugate of the antibodies to exotoxin A with beta-lactamase from Bacillus licheniformis 749/c was prepared by linking glutaric aldehydes. The conjugate showed high immunospecific and enzymatic activity and was used for competitive solid phase immunoenzymatic assay. Sensitivity of the assay provided determination of exotoxin A in concentration of 20 ng/ml. It was used for determining P. aeruginosa exotoxin A in culture fluids.

[Immunoenzyme demonstration of viruses and virus-specific antibodies by using conjugates based on gene engineering-produced beta-lactamase]

Enzyme immunoassays for the detection of viral antigens and virus-specific antibodies in biological samples have been described. Molecular complexes of antibodies and beta-lactamase (penicillinase) have been used as anti-specific conjugates. To synthesize the conjugate, the enzyme obtained with the aid of genetic engineering has been used. Enzyme immunoassays have been tested for the indication of the influenza virus and virus-induced specific antibodies. Enzyme immunoassays were shown to possess certain advantages (e.g., the use of simple and nontoxic substrate) along with the sensitivity identical to that of other methods, employing peroxidase-based conjugates.

[Solid-phase immunoenzyme analysis of insulin using Bacillus licheniformis 749/c beta-lactamase and horseradish peroxidase as markers]

Two modifications of solid phase enzyme immunoassay (EIAA) for insulin with the use of beta-lactamase from B. licheniformis 749/c and horse radish peroxidase as the markers were developed. beta-Lactamase and peroxidase conjugates with insulin were prepared with the glutaric aldehyde and periodate methods respectively. Both the conjugates were stable and preserved high immunospecific and enzymatic activity. Sensitivity of EIAA with the use of the beta-lactamase or peroxidase as the markers was the same and amounted to 15 ng/ml of insulin. However, with the use of the beta-lactamase in EIAA not only spectrophotometric recording but also visual registration of the results was possible.

[Field trial of an immunoenzyme method using beta-lactamase as the monoclonal antibody marker for the capsular antigen of the plague microbe]

Beta-lactamase (penicillinase) has been used as a marker of monoclonal antibodies in the enzyme immunoassay made with a view to the detection of Y. pestis capsular antigen and antibodies to it. The trial of the enzyme immunoassay with the use of the beta-lactamase conjugate in laboratories and under field conditions has revealed the advantage of this assay over hemagglutination tests commonly used for this purpose.

Influence of technical factor variations on serum inhibition and bactericidal titers

The influence of technical factor variations on serum bactericidal and serum inhibitory titers was studied by using Staphylococcus aureus clinical isolates versus oxacillin-spiked human serum. Parallel tests, both with and without the use of beta-lactamase in count plates to inactivate oxacillin carryover, were performed with a conventional macrodilution approach, a carefully controlled macrodilution procedure, and a standard microdilution method. Careful control of technical factor variations diminished the incidence of low serum bactericidal titers and decreased the dispersion of results, a finding corollary to the known influence of technical factor variations on the measurement of MBCs. The incorporation of beta-lactamase into count plates resulted in a shift of serum bactericidal titers to lower values. The microdilution method appeared to be least influenced by technical variations and, with the addition of beta-lactamase to count plates, provided the best results.

Tertiary structural similarity between a class A beta-lactamase and a penicillin-sensitive D-alanyl carboxypeptidase-transpeptidase

beta-Lactam antibiotics--the penicillins, cephalosporins and related compounds--act by inhibiting enzymes that catalyse the final stages of the synthesis of bacterial cell walls. Recent crystallographic studies of representative enzymes are beginning to reveal the structural bases of antibiotic specificity and mechanism of action, while intensive efforts are being made to understand the beta-lactamase enzymes that are largely responsible for bacterial resistance to these antibiotics. It has been suggested that the beta-lactamases and beta-lactam target enzymes may be evolutionarily related and some similarity of amino-acid sequence around a common active-site serine residue supports this idea. We present here the first evidence from a comparison of three-dimensional structures in support of this hypothesis: the structure of beta-lactamase I from Bacillus cereus is similar to that of the penicillin-sensitive D-alanyl-D-alanine carboxypeptidase-transpeptidase from Streptomyces R61.

[Use of beta-lactamase from Bacillus licheniformis 749/C for solid-phase immunoenzyme analysis]

beta-Lactamase from Bacillus licheniformis 749/c was used as a marker for ELISA. Conjugates of the beta-lactamase with the capsule antigen of the plague causative agent and with the monoclonal antibodies to it were prepared by glutaric aldehyde "linking". The conjugates preserved high immunospecific and beta-lactamase activity. High sensitivity of the modification of ELISA allowed detecting up to 8 ng/ml of the capsule antigen of the plague causative agent. The enzymatic activity of the beta-lactamase was determined microiodometrically which provided visual recording of the results of ELISA.

Effects of sulphate and urea on the stability and reversible unfolding of beta-lactamase from Staphylococcus aureus. Implications for the folding pathway of beta-lactamase

The reversible denaturation by urea of beta-lactamase from Staphylococcus aureus was followed in the presence and absence of ammonium sulphate by circular dichroism studies, difference absorption spectroscopy and measurement of enzyme activity. The multiple unfolding and refolding transitions demonstrate the existence of a thermodynamically stable state of intermediate conformation in equilibrium with the native (N) and fully unfolded (U) states. Its physical properties show that it is identical to the state H found on denaturation by guanidinium chloride. State H is 10.1 (+/-1.5) kJ mol-1 less stable than the native state and 10.1 (+/-1.6) kJ mol-1 more stable than the unfolded state. Ammonium sulphate shifts both the N in equilibrium H and H in equilibrium U transitions to concentrations of urea higher by 5.3 M per mole of sulphate. It has markedly different effects on the thermodynamic stabilities of states N and H, making delta G'N-H, O and delta G'H-U, O more negative by 41 kJ mol and 20 kJ mole, respectively, per mole of ammonium sulphate. The change in equilibrium constant for the N-H transition is reflected almost exclusively in a dramatic change of the unfolding rate constant, which is decreased by a factor of 10(11) on addition of 1.4 M-sulphate. The presence of the substrate benzyl penicillin has little effect on the equilibria or kinetics of the N-H transition. The results are discussed in terms of the nature of the N-H transition and of the ordering of intermediate states on the folding pathway.

An enzymatic assay for monitoring serum, cerebrospinal fluid, and urine concentration of beta-lactam antibiotics

August 29/October 24, 1984 An enzymatic assay for the determination of the concentrations of various beta-lactam antibiotics in serum, urine, and cerebrospinal fluid samples is described. Recently developed beta-lactam derivatives are used as competitive inhibitors of the breakdown of the labile coloured beta-lactam compound PADAC, which serves as the substrate for the various beta-lactamases. Under the conditions of the assay, there is effectively no interference due to the matrix. Moreover, the assay is not influenced by other antibiotics such as aminoglycosides, macrolides, ansamycines, tetracyclines, fusidic acid or fosfomycin. The C.V.s for within-run precision ranged from 3.7% to 4.4%, depending on the beta-lactam derivative. The sensitivity of the assay is at least comparable with that of conventional procedures. Excellent correlations were observed between the enzymatic and the microbiological procedures; correlation coefficients: r = 0.988 for 22 imipenem samples, r = 0.968 for 16 cefotaxime samples, and r = 0.989 for 16 piperacillin samples routinely sent to our laboratory.

Characterization of clinical isolates of Haemophilus influenzae type b for heterogeneous populations of susceptibility to ampicillin

In this study 80 clinical isolates of Haemophilus influenzae type b from 60 patients were used to analyze if heterogeneous populations of ampicillin resistant and sensitive cells were simultaneously present within each strain and to determine how common this phenomenon was among clinical isolates. A total of 50 ampicillin sensitive clinical isolates were screened for resistance to this antibiotic. It was observed that 32 ampicillin sensitive strains did not contain resistant subpopulations. Furthermore, even with the inducement of resistant subgroups to proliferate under antibiotic-mediated selection using maximum subinhibitory concentrations of ampicillin, no subpopulations of resistant cells were discovered among 18 additional strains. In order to determine whether ampicillin resistance was stable in beta-lactamase-producing H. influenzae clinical isolates, 20 strains from 16 patients were examined. No tendency to segregate into a heterogeneous population of sensitive and resistant clones was found. Furthermore, ampicillin resistance was still uniformly expressed after the treatment of ten strains with the curing agent acridine orange. These results suggest that after extensive evaluation no heterogeneous populations existed with ampicillin resistant and sensitive H. influenzae clinical isolates, indicating that this phenomenon is not a prevalent one.

A coupled enzyme assay for isopenicillin N synthetase

The development of a coupled enzyme assay for the determination of isopenicillin N synthetase activity in purified extracts from Cephalosporium acremonium was described. Isopenicillin N formed from its precursor, delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine (ACV), by the synthetase was hydrolyzed by beta-lactamase I to the corresponding penicilloic acid. Automatic titration of the acid with standard sodium hydroxide delivered by a pH-stat gave a continuous plot of product formed vs time. This assay has been used in kinetic studies and to determine the effects of pH, ionic strength, and temperature on the enzyme's activity.

Crystallization and preliminary X-ray data for the exocellular beta-lactamase of Bacillus licheniformis 749/C

The exocellular beta-lactamase from Bacillus licheniformis 749/C has been crystallized from polyethylene glycol solution at pH 5.5. An X-ray examination of the monoclinic crystals shows the space group is P21, with unit cell dimensions a = 66.77 A, b = 93.77 A, c = 43.57 A and beta = 104.5 degrees. The asymmetric unit consists of two molecules of 28,500 Mr each. The crystals are suitable for structure analysis to at least 2 A resolution.