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PubMed1987

beta-Lactamase production in experimental endocarditis due to aminoglycoside-resistant Streptococcus faecalis.

We used a beta-lactamase-producing (beta L+) strain of Streptococcus faecalis that also had high levels of resistance to all aminoglycosides to induce experimental endocarditis in rats. The rats were treated for five or 10 days with procaine penicillin, vancomycin, gentamicin, rifampin, or ciprofloxacin (alone or in various combinations), or with penicillin plus clavulanic acid. The levels of penicillin in serum and vegetations declined rapidly in the beta L+-infected rats treated with procaine penicillin alone, unlike the sustained levels of penicillin in either beta L- -infected rats treated with procaine penicillin or beta L+-infected rats treated with penicillin plus clavulanic acid. For the beta L+-infected rats, the enterococcal counts in vegetations were significantly reduced (greater than 3 log10 cfu/g) only by vancomycin and by penicillin plus clavulanic acid. The efficacy of the latter regimen probably resulted from the inhibition of penicillin inactivation by clavulanic acid in vegetations infected with the beta L+ strain. Our in vivo findings document the biologic significance of beta-lactamase production.

Aminoglycosides↗
PubMed1995

Diversity of methicillin-resistant Staphylococcus aureus isolated in a Canadian hospital.

Three neonates and three other patients located elsewhere in the hospital became infected with Staphylococcus aureus. Initial automated microdilution susceptibility testing with oxacillin and disk diffusion testing with amoxicillin-clavulanic acid indicated the isolates had borderline oxacillin resistance (MICs 4 micrograms/ml), presumably due to hyperproduction of beta-lactamase. Chromosomal DNA restriction fingerprinting and phage typing revealed the neonatal isolates to be identical; whereas, the other patients were infected with three different strains. Further analysis of the four strains by Southern hybridization with a mecA specific oligoprobe and a quantitative beta-lactamase assay demonstrated that two strains carried the mecA gene (coding for low affinity penicillin-binding protein 2a), and two strains were hyperproducers of beta-lactamase, including one which was mecA gene positive. One strain neither carried the mecA gene nor hyperproduced beta-lactamase. The two mecA gene positive strains displayed oxacillin MICs of 16 micrograms/ml on dilution susceptibility testing in 4% NaCl supplemented Mueller-Hinton agar. Hence, they were considered intrinsically methicillin-resistant Staphylococcus aureus. Both oxacillin and amoxicillin-clavulanic acid MICs were increased on NaCl supplementation. Results of amoxicillin-clavulanic acid disk diffusion susceptibility testing did not correlate with quantitative beta-lactamase production. It is recommended that clinical laboratories do not use amoxicillin-clavulanic acid disk diffusion assays to differentiate suspected borderline resistance due to beta-lactamase hyperproduction from mecA gene expression of PBP-2a since additional mechanisms may account for resistance.

Adult↗
PubMed2000

Expanded-spectrum antibiotics with preterm premature rupture of membranes.

OBJECTIVE: To compare maternal infection rates, neonatal sepsis rates, and bacterial resistance patterns in cases of neonatal sepsis for three antibiotic protocols for women with preterm premature rupture of membranes (PROM). METHODS: From January 1, 1988 to February 28, 1998, women with preterm PROM not requiring immediate delivery were treated according to one of three antibiotic protocols. During three distinct periods, patients received no antibiotics, intravenous ampicillin for 48 hours followed by oral amoxicillin, or intravenous ticarcillin-clavulanic acid for 48 hours followed by oral amoxicillin-clavulanic acid. Rates of chorioamnionitis, endometritis, and neonatal sepsis were compared, as were antimicrobial resistance patterns. Statistical analysis was done using chi(2) analysis, Fisher exact test, and the log-likelihood ratio test. The Bonferroni correction was used for multiple comparisons. RESULTS: During the three periods, preterm PROM was diagnosed in 1695 women. The incidence of endometritis was lower during the third (5.3%) compared with the first (15.1%, P <.001) and second (11.6%, P <.001) protocols. Chorioamnionitis rates were 13.6%, 12.7%, and 15.6% (P =.34) for the first, second, and third periods, respectively, and neonatal sepsis rates were 2.2%, 0.6%, and 1.1% (P =.08), respectively. Neonatal sepsis with gram-negative (P =.02) and ampicillin-resistant (P =.04) organisms was more likely when mothers received antepartum ampicillin or ticarcillin-clavulanic acid. CONCLUSION: Antibiotic therapy for patients with preterm PROM was associated with a decrease in the rate of endometritis and a trend toward less neonatal sepsis but an increase in the proportion of gram-negative and ampicillin-resistant organisms causing neonatal sepsis.

Adult↗
PubMed1988

Beta-lactamase inhibitors from laboratory to clinic.

beta-Lactamases constitute the major defense mechanism of pathogenic bacteria against beta-lactam antibiotics. When the beta-lactam ring of this antibiotic class is hydrolyzed, antimicrobial activity is destroyed. Although beta-lactamases have been identified with clinical failures for over 40 years, enzymes with various abilities to hydrolyze specific penicillins or cephalosporins are appearing more frequently in clinical isolates. One approach to counteracting this resistance mechanism has been through the development of beta-lactamase inactivators. beta-Lactamase inhibitors include clavulanic acid and sulbactam, molecules with minimal antibiotic activity. However, when combined with safe and efficacious penicillins or cephalosporins, these inhibitors can serve to protect the familiar beta-lactam antibiotics from hydrolysis by penicillinases or broad-spectrum beta-lactamases. Both of these molecules eventually inactivate the target enzymes permanently. Although clavulanic acid exhibits more potent inhibitory activity than sulbactam, especially against the TEM-type broad-spectrum beta-lactamases, the spectrum of inhibitory activities are very similar. Neither of these inhibitors acts as a good inhibitor of the cephalosporinases. Clavulanic acid has been most frequently combined with amoxicillin in the orally active Augmentin and with ticarcillin in the parenteral beta-lactam combination Timentin. Sulbactam has been used primarily to protect ampicillin from enzymatic hydrolysis. Sulbactam has been used either in the orally absorbed prodrug form as sultamicillin or as the injectable combination ampicillin-sulbactam. Synergy has been demonstrated for these combinations for most members of the Enterobacteriaceae, although those organisms that produce cephalosporinases are not well inhibited. Synergy has also been observed for Neisseria gonorrhoeae, Haemophilus influenzae, penicillinase-producing Staphylococcus aureus, and anaerobic organisms. These antibiotic combinations have been used clinically to treat urinary tract infections, bone and soft-tissue infections, gonorrhea, respiratory infections, and otitis media. Gastrointestinal side effects have been reported for Augmentin and sultamicillin; most side effects with these agents have been mild. Although combination therapy with beta-lactamase inactivators has been used successfully, the problem of resistance development to two agents must be considered. Induction of cephalosporinases can occur with clavulanic acid. Permeability mutants could arise, especially with added pressure from a second beta-lactam.(ABSTRACT TRUNCATED AT 250 WORDS)

Anti-Bacterial Agents↗
PubMed1995

Purification and characterization of clavaminate synthase from Streptomyces antibioticus. A multifunctional enzyme of clavam biosynthesis.

Clavaminate synthase (CS), a key enzyme in the clavulanic acid biosynthetic pathway, has been purified to electrophoretic homogeneity from Streptomyces antibioticus (Tü 1718), a species that does not produce clavulanic acid. A comparison of the physical and kinetic properties of clavaminate synthase from S. antibioticus (CS3) and the two isozymes from Streptomyces clavuligerus (CS1 and CS2) has been conducted. In oxidative reactions requiring the co-substrates O2, alpha-ketoglutaric acid, and catalytic Fe2+, both CS1 and CS2 catalyze three distinct transformations, the hydroxylation of deoxyguanidinoproclavaminic acid to guanidinoproclavaminic acid, and the cyclization and desaturation of proclavaminic acid to clavaminic acid. We have demonstrated that CS3 from S. antibioticus also catalyzes these three oxidations. The apparent molecular mass of CS3 from matrix-assisted laser desorption mass spectrometry is 35,839 +/- 36 Da. The enzyme is a monomer in solution as determined by gel filtration chromatography. Analysis of the four possible proclavaminic acid diastereomers confirmed the absolute configuration of the substrate to be 2S,3R. Based upon N-terminal sequence comparisons among the three proteins, CS3 possesses the higher degree of homology with the CS1 isozyme from S. clavuligerus. Although previously associated solely with clavulanic acid biosynthesis, we propose these findings and recent precursor incorporation data support the view that clavaminate synthase plays a critical role in the biosynthesis of the clavam metabolites.

Amino Acid Sequence↗
PubMed1996

Cost saving of 5-day therapy with cefpodoxime proxetil versus standard 10-day beta-lactam therapy for recurrent pharyngotonsillitis in adults. A prospective general practice study.

A prospective economic evaluation was undertaken as part of a randomised clinical trial conducted in French general practice. Its aim was to compare the costs and therapeutic outcomes of a 5-day course of cefpodoxime proxetil 100 mg twice daily with 10-day courses of phenoxymethylpenicillin (penicillin V) 1 MIU 3 times daily and amoxicillin-clavulanic acid 500/125 mg 3 times daily for the treatment of recurrent pharyngotonsillitis in 575 adults. Over the 6-month study period, the total cost to society per patient treated with cefpodoxime proxetil was 123 French francs (FF; 1993 values) lower than that for patients treated with phenoxymethylpenicillin and FF227 lower than that for patients treated with amoxicillin-clavulanic acid. This cost saving was primarily attributable to a lower initial drug acquisition cost, and a reduction in the cost associated with lost productivity and general practitioner consultations. Furthermore, as a consequence of a lower relapse rate, the cost-saving ratio for cefpodoxime proxetil, expressed as FF per month free of recurrence, was FF50 less than for phenoxymethylpenicillin and FF60 less than for amoxicillin-clavulanic acid. Thus, a 5-day course of cefpodoxime proxetil is likely to be less costly for treatment of pharyngotonsillitis in the general practice setting than standard 10-day courses of phenoxymethylpenicillin and amoxicillin-clavulanic acid.

Adult↗
PubMed1985

In vitro susceptibilities and beta-lactamase production of 53 clinical isolates of Branhamella catarrhalis.

We tested 53 clinical isolates of Branhamella catarrhalis recovered from patients with respiratory symptoms to determine the susceptibility of the isolates to 25 antimicrobial agents, including the newer beta-lactam antibiotics. Of the 53 strains, 46 (86.7%) were beta-lactamase producers. All the strains were susceptible to the majority of the new penicillins and cephalosporins. The combinations of amoxacillin-clavulanic acid and ticarcillin-clavulanic acid were also very active against the beta-lactamase-producing strains.

Anti-Bacterial Agents↗
PubMed2001

Antimicrobial resistance surveillance of gram-negative bacteria isolated from intensive care units of four different hospitals in Turkey. Evaluation of the prevalence of extended-spectrum and inducible beta-lactamases using different E-test strips and direct induction methods.

BACKGROUND: The aim of this study was to determine the antimicrobial resistance of gram-negative rods (GNRs) isolated from surgical intensive care units and to establish the prevalence of extended-spectrum beta-lactamases (ESBLs) and inducible beta-lactamases (IBLs). We also wished to determine the widespread beta-lactam substrate in ESBL-positive GNRs by two different E-test strips and to discuss the value of the routine utilization of these substrates together. METHODS: Out of 348 nosocomial gram-negative strains isolated with similar methods, 236 strains with resistance to the beta-lactam group of antimicrobials using the E-test method were included in this study. Two different strips were used for the detection of ESBLs: cefotaxime/cefotaxime + clavulanic acid (CT/CTL) and ceftazidime/ceftazidime + clavulanic acid (TZ/TZL). For IBLs, the double-disk method was used. RESULTS: The order of frequency of the strains, starting with the most frequent, was Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa. In the 236 strains, the ESBL positivity rate was found to be 19.5% with TZ/TZL and CT/CTL strips, while it was 13.2% for IBL in 348 strains. Seventy-one percent of ESBL-positive strains gave parallel results with TZ/TZL and CT/CTL. ESBL positivity with only TZ/TZL or only CT/CTL was found to be 18 and 8%. CONCLUSIONS: Our study showed that except for imipenem, amikacin and ciprofloxacin, there was a high resistance to other antimicrobials, and multiresistance rates were increased in the strains in which ESBLs and IBLs were detected. In particular, the increasing prevalence of ESBLs in K. pneumoniae and IBLs in P. aeruginosa emphasizes the importance of the problem of infection control and antibiotic administration policies. Although it was seen that the prevalence of substrate templates in the detection of ESBL positivity was similar, we think that it is more useful to use two different strips together to obtain precise results.

Anti-Bacterial Agents↗
PubMed1988

Clinical pharmacokinetics of enzyme inhibitors in antimicrobial chemotherapy.

The effectiveness of some antimicrobial agents can be enhanced by using them in combination; such combinations are termed synergistic. Where one compound potentiates the effect of a second drug they may be coformulated. Inhibition of the bacterial degradation of an active antimicrobial is the basis of clavulanate and sulbactam-potentiated penicillin combinations, and inhibition of degradative pathways in the host is the rationale behind imipenem/cilastatin therapy. Trimethoprim/sulphonamide combinations depend on the maintenance of an effective ratio for synergistic action. In order to achieve potentiation the coformulated drugs should have similar pharmacokinetics. Trimethoprim was originally matched with sulphamethoxazole, since these two drugs have similar elimination half-lives, but the significantly poorer penetration of sulphonamides, their greater non-renal clearance, the emergence of resistance, and the adverse reactions attributable to them argue against the rationale that underlies their coformulation. Time-dependent inhibition of bacterial beta-lactamases by clavulanic acid and sulbactam has extended the use of penicillins which are highly susceptible to beta-lactamase inactivation. The beta-lactamase inhibitors must penetrate to the same extent as the penicillin used with them, and be present long enough to effect inhibition; thus, rapid penetration, similar or slower elimination and equivalent volume of distribution are necessary. These requirements are met for amoxycillin/clavulanic acid, ticarcillin/clavulanic acid and ampicillin/sulbactam combinations. Clavulanic acid is absorbed orally and is given with amoxycillin. However, since sulbactam is labile by this route, the combination of sulbactam with ampicillin to form the prodrug sultamicillin has been necessary to enable an oral form to be developed. Imipenem is metabolised by renal brush-border dehydropeptidases, and may cause proximal tubular necrosis. Cilastatin was designed to inhibit this metabolism, which it effectively does, thereby both potentiating the effect of imipenem and avoiding toxicity. Appropriate matching of the kinetics of coformulated drugs is intended to maximise potentiation and minimise the risk of emergent resistance. The kinetics of the above combinations are discussed in the light of these requirements and the effects of age and disease.

Anti-Bacterial Agents↗
PubMed1991

In vitro activities of 36 antimicrobial agents against clinically isolated Bacteroides fragilis.

Thirty-six antimicrobial agents were evaluated for in vitro activities against 100 clinical isolates of Bacteroides fragilis. The minimal inhibitory concentration (MIC) of each agent for each isolate was determined by the agar dilution method. Among 25 beta-lactam antibiotics, the most active agent was imipenem with an MIC90 and a geometric mean of 1 and 0.15 micrograms/ml, respectively; followed by ticarcillin-clavulanic acid, and amoxicillin-clavulanic acid. Ampicillin-sulbactam, piperacillin-tazobactam, moxalactam, and flomoxef were the next most active agents. Piperacillin, ticarcillin, ceftizoxime, cefotaxime, cefuzonam, cefoxitin, and cefmetazole were equally active with the MIC50s ranging from 4 to 16 micrograms/ml, and MIC90s ranging from 32 to greater than or equal to 256 micrograms/ml. The remaining 10 beta-lactam antibiotics, ampicillin, amoxicillin, cefazolin, cefuroxime, cefoperazone, cefmenoxime, ceftazidime, cefpirome, aztreonam, and carumonam were less active. All isolates were resistant to cefotiam at a low breakpoint. Among 6 quinolones, ciprofloxacin was the most active agent with an MIC50 and an MIC90 of 4 and 16 micrograms/ml, respectively. All isolates were resistant to nalidixic acid, pipemidic acid, cinoxacin, enoxacin, and norfloxacin. Among 5 frequently used agents, chloramphenicol, ornidazole, and metronidazole were the most effective agents which inhibited 100% of the isolates at 8, 2, and 2 micrograms/ml, respectively; while clindamycin and minocycline had less activity.

4-Quinolones↗
PubMed1984

[Induction of beta-lactamases in Enterobacter cloacae with beta-lactam antibiotics].

The induction potency of various beta-lactam compounds was studied in a clinical isolate which exhibited resistance against most beta-lactam compounds; however, spontaneous beta-lactamase production was only marginal in this strain. In general, all beta-lactam derivatives included in this study possessed induction potency independent of the nucleus of the compound. N-formimidoyl thienamycin, the penem compound Sch 29482, 6-aminopenicillanic acid, and clavulanic acid proved to be the most potent inducers. With the exception of mezlocillin and ceftazidime there was a correlation between the concentration of the compound and the induction potency. Combination of two beta-lactam antibiotics resulted in an addition of the induction potency of each one. With respect to the considerable amount of enzyme that can be induced the development of resistance even against newer compounds fairly stable against the attack of beta-lactamases can be explained.

Anti-Bacterial Agents↗
PubMed1989

The role of beta-lactamase in mixed infections in mice in relation to treatment with ampicillin.

Beta-lactamase-producing Staphylococcus aureus and Bacteroides fragilis in a localized mixed infection has been found to degrade the beta-lactam antibiotic at the focus of infection, thus protecting both the bacteria and pathogens susceptible to the antibiotic. To determine if beta-lactamase produced by Hemophilus influenzae and Branhamella catarrhalis have similar importance in mixed infections, a thread infection model in mice was used to evaluate the capacity of beta-lactamase produced by S. aureus, B. catarrhalis, or H. influenzae to hydrolyze ampicillin in a mixed infection with Streptococcus pneumoniae in mice. For both S. aureus and B. catarrhalis, the ampicillin concentrations at infection sites where beta-lactamase was produced were lower than at sites where beta-lactamase was not produced; however, this difference was not found when clavulanic acid was added to the ampicillin. In mixed infections with strains that did not produce beta-lactamase, ampicillin concentrations were similar with or without clavulanic acid. S. aureus was the best "protector" followed by B. catarrhalis. The beta-lactamase produced by H. influenzae failed to protect the S. pneumoniae. No bactericidal effect of clavulanic acid was found.

Ampicillin↗
PubMed1988

Comparative pharmacokinetics of sulbactam/ampicillin and clavulanic acid/amoxycillin in human volunteers.

In this study, the pharmacokinetic parameters of 2 different beta-lactamase inhibitors (sulbactam and clavulanic acid) in combination with 2 different aminobenzylpenicillins (ampicillin and amoxycillin) were compared. The study involved 10 healthy volunteers who received sulbactam 250 mg plus ampicillin 500 mg intravenously, clavulanic acid 100 mg plus amoxycillin 500 mg intravenously, sultamicillin equivalent to sulbactam 294 mg plus ampicillin 440 mg orally, and clavulanic acid 125 mg plus amoxycillin 500 mg orally in a crossover, randomised trial. Serum and urine concentrations of ampicillin, amoxycillin and clavulanic acid were assayed by agar diffusion test, and the concentrations of sulbactam by gas chromatography with mass spectrometry. Pharmacokinetic parameters were calculated according to open 1- and 2-compartment models. Test results showed that the addition of sulbactam significantly increases the bioavailability of oral ampicillin when the 2 drugs are administered in the form of the prodrug sultamicillin. Also, sulbactam does not interfere with the kinetics of intravenous ampicillin but increases the absorption of oral ampicillin.

Administration, Oral↗
PubMed2000

[Antibiotic management of acute otitis media. New recommendations].

FAILURES OF ANTIBIOTIC TREATMENT: The number of failures after treatment of acute middle ear infections with the 2 main antibiotics prescribed (amoxicillin and the combination amoxicillin-clavulanic acid) is on the rise. These failures appear to be related to increased resistance of the 2 principal pathogens, pneumococci and Hemophilus influenzae. A NEW FORMULATION: In order to reduce the rate of failure, it has been necessary to both increase the dose of penicillin to overcome the reduced susceptibility of pneumococci to penicillin and to prescribe a beta-lactam because of the frequent isolation of beta-lactamase producing Hemophilus influenzae. A new formulation has been developed where the amoxicillin-clavulanic acid dose is 14 to 1. This allows a daily dose of 80 mg/kg for amoxicillin and 6.4 mg/kg for clavulanic acid. In one open multicentric study including 51 pediatric patients aged 3 to 48 months with acute middle ear infections, it was demonstrated that this new formulation can be very effective in eradicating the causal agents of acute middle ear infections, including pneumococci and penicillin-resistant Hemophilus. RECOMMENDATIONS FOR GOOD EFFICACY: Amoxicillin must always be prescribed, either alone or in combination with clavulanic acid, at the dose of 45 to 50 mg/kg b.i.d. the amoxicillin-clavulanic acid combination should be preferred for children under 2 years due to the risk of beta-lactamase producing Hemophilus.

Amoxicillin-Potassium Clavulanate Combination↗
PubMedDate not supplied

Induction/inhibition of chromosomal beta-lactamases by beta-lactamase inhibitors.

Many species of gram-negative bacteria produce chromosomal beta-lactamases that can be induced to high-level expression by exposure to beta-lactam antibiotics. Fifty-four strains of Escherichia coli, Enterobacter, Proteus, Citrobacter, and Morganella were examined for beta-lactamase inducibility by clavulanic acid, sulbactam, YTR 830, ampicillin, and cefoxitin. Cefoxitin proved to be the most potent inducer, affecting most of the strains of Enterobacter and Morganella. Clavulanic acid induced 30% of all strains studied. Sulbactam and YTR 830 did not induce measurable levels of beta-lactamases. Inhibition of some chromosomal beta-lactamases by sulbactam and YTR 830 was demonstrated, whereas inhibitory activity by clavulanic acid was found only in Proteus and Citrobacter.

Ampicillin↗
PubMed2006

Effect of the inhibitor-resistant M69V substitution on the structures and populations of trans-enamine beta-lactamase intermediates.

The objective of this study was to determine the molecular factors that lead to beta-lactamase inhibitor resistance for the M69V variant in SHV-1 beta-lactamase. With mechanism-based inhibitors, the beta-lactamase forms an acyl-enzyme intermediate that consists of a trans-enamine derivative in the active site. This study focuses on these intermediates by introducing the E166A mutation that greatly retards deacylation. Thus, by comparing the properties of the E166A and M69V/E166A forms, we can explore the consequences of the resistance mutation at the level of the enamine acyl-enzyme forms. The reactions between the beta-lactamase and the inhibitors tazobactam, sulbactam, and clavulanic acid are followed in single crystals of the enzymes by using a Raman microscope. The resulting Raman difference spectroscopic data provide detailed information about conformational events involving the enamine species as well as an estimate of their populations. The Raman difference spectra for each of the inhibitors in the E166A and M69V/E166A variants are very similar. In particular, detailed analysis of the main enamine Raman vibration near 1595 cm(-1) reveals that the structure and flexibility of the enamine fragments are essentially identical for each of the three inhibitors in E166A and in the M69V/E166A double mutant. This finding is in accord with the X-ray-derived structures, presented herein at 1.6-1.75 A resolution, of the trans-enamine intermediates formed by the three inhibitors in M69V/E166A. However, a comparison of Raman results for M69V/E166A and E166A shows that the M69V mutation results in a 40%, 25%, and negligible reductions in the enamine population when the beta-lactamase crystals are soaked in 5 mM tazobactam, clavulanic acid, and sulbactam solutions, respectively. The levels of enamine from tazobactam and clavulanic acid can be increased by increasing the concentrations of inhibitor in the mother liquor. Thus, the sensitivity of population levels to the inhibitor concentration in the mother liquor focuses attention on the properties of the encounter complex preceding acylation. It is proposed that for small ligands, such as tazobactam, sulbactam, and clavulanic acid, the positioning of the lactam ring in the active site in the correct orientation for acylation is only one of a number of poorly defined conformations. For tazobactam and clavulanic acid, the correctly oriented encounter complex is even less likely in the M69V variant, leading to a reduction in the level of inhibition of the enzyme via formation of the acyl-enzyme intermediate and the onset of resistance. Analysis of the X-ray structures of the three intermediates in M69V/E166A demonstrates that, compared to the structures for the E166A form, the oxyanion hole becomes smaller, providing one explanation for why acylation may be less efficient following the M69V substitution.

Amino Acid Substitution↗
PubMedDate not supplied

[Detection of hyperproduction of chromosomal beta-lactamase in strains of Escherichia coli, Enterobacter cloacae and Pseudomonas aeruginosa].

In order to show up the hyperproduction of chromosomic beta-lactamases in strains of Enterobacteriaceae and Pseudomonas aeruginosa we have tested a variant of a technique proposed by Medeiros et al. It is a qualitative technique and, the modification introduced allows errors of interpretation to be avoided, when the strain is a producer of plasmidic beta-lactamase. It is based on evaluating the amount of beta-lactamase in a culture, measured in time taken for the hydrolysis of nitrocefin, with or without the addition of clavulanic acid. We present the results obtained in 526 selected strains: 271 E. coli, 116 E. cloacae and 139 P. aeruginosa. One hundred and twenty for strains hydrolyzed the nitrocefin in the absence of clavulanic acid within 60 seconds. Only 52 (41.94%) of these strains did it when clavulanic acid was present; all of them have been qualified as hyperproducers according to susceptibility to beta-lactam antibiotics and the study and identification of the beta-lactamases by analytic isoelectrofocusing. The hydrolysis was evident before the 15 seconds in the 80% of hyperproducer strains. No false positive results were observed.

Cephalosporins↗
PubMed1986

Timentin and beta-lactamases.

Ticarcillin is resistant to the action of cephalosporinases, which explains its biological activity on a large number of bacterial species, including cephalosporinase-producing Enterobacteriaceae and Pseudomonas aeruginosa. Nevertheless, its antibacterial activity is often limited by the action of some beta-lactamases, mostly plasmid-mediated penicillinases. Clavulanic acid by itself has poor antibacterial activity, but its most important property is to inhibit and inactivate beta-lactamases. The inhibitory properties of clavulanic acid were studied on a large number of beta-lactamases. The penicillinases produced by Staphylococcus aureus, the plasmid-mediated beta-lactamases such as the TEM-type, the chromosomally-mediated penicillinases from Klebsiella pneumoniae and other closely-related beta-lactamases, and a few chromosomally-mediated cephalosporinases, such as that produced by Proteus vulgaris, are powerfully inhibited by clavulanic acid. The plasmid-mediated penicillinases of OXA type and most of the chromosomally-mediated cephalosporinases, such as that produced by Escherichia coli (Amp C), are less or poorly inhibited. Moreover, clavulanic acid has some cephalosporinase-inducing properties. These properties are in good agreement with the bacteriological properties of Timentin.

Bacterial Proteins↗