Beta-lactamase inhibitors from laboratory to clinic

Prediction of piperacillin-tazobactam susceptibility among Enterobacteriaceae, Pseudomonas aeruginosa, and other bacteria using ticarcillin-clavulanic acid, ceftazidime, and other broad-spectrum antimicrobial in vitro test results

The ability of various in vitro beta-lactam susceptibility test results to predict the susceptibility of piperacillin-tazobactam (a new beta-lactam-beta-lactamase inhibitor combination) was assessed using more than 46,000 recent clinical isolates. The organisms were tested by reference-quality National Committee for Clinical Laboratory Standards (NCCLS) broth microdilution procedures and interpreted by the currently published NCCLS criteria. The recommended antimicrobial tests that would accurately predict the piperacillin-tazobactam in vitro efficacy had an overall very major, false-susceptible rate of only 0.6% (< or = 1.5% is acceptable). The following drug tests can be used to judge piperacillin-tazobactam activity and spectrum (low patient risk) conservatively: for Enterobacteriaceae use ticarcillin-clavulanic acid results (0.6% very major error); for Pseudomonas aeruginosa use piperacillin (0.1%) results; for enterococci use ampicillin or ampicillin-sulbactam (1.8%) results; for Haemophilus influenzae and Moraxella catarrhalis use cefotaxime or cefuroxime or ceftriaxone (1.5%); and for staphylococci use oxacillin by NCCLS recommendations. When the piperacillin-tazobactam testing reagents become available, the direct testing of this combination should be applied to relevant clinical isolates. The piperacillin-tazobactam break points should be reassessed as indicated by the cited minimum inhibitory concentration population analysis to improve predictive accuracy; H. influenzae susceptibility modified to < or = 2/4 micrograms/ml and Enterococcus species susceptibility tested at < or = 16/4 micrograms.

Extrachromosomal resistance in gram-negative organisms: the evolution of beta-lactamase

beta-Lactamases are the major defense used by bacteria to overcome the effects of penicillins, cephalosporins and related beta-lactam antibiotics. In the antibiotic era, the enzymes have evolved to become more prevalent, to appear in new hosts, to be expressed at higher levels, to be acquired by plasmids and to change catalytic properties to increase affinity for what were meant to be nonhydrolysable substrates or to reduce affinity for beta-lactamase inhibitors.

In vitro activity of the tribactam GV104326 against gram-positive, gram-negative, and anaerobic bacteria

GV104326 is the first member of a new class of antibiotics (tribactams) selected for development. It combines a particularly broad spectrum (including gram-negative and gram-positive aerobes and anaerobes) with high potency, resistance to beta-lactamases, and complete stability to dehydropeptidases. Comparative MICs were determined for GV104326 against 415 recent clinical isolates (including beta-lactamase producers), using representative antibacterial agents (imipenem, amoxicillin-clavulanic acid, cefpirome, ciprofloxacin, gentamicin, and erythromycin). GV104326 was particularly active against gram-positive bacteria; in general, its in vitro activity was equivalent to that of imipenem, equivalent to or better than that of amoxicillin-clavulanic acid, and superior to that of cefpirome, ciprofloxacin, and erythromycin. Against gram-negative bacteria, GV104326 possessed activity similar to that of imipenem and cefpirome against enterobacteria and Haemophilus spp. but its activity was superior to that of amoxicillin-clavulanic acid. GV104326 showed excellent antianaerobe activity. GV104326 was stable to all clinically relevant beta-lactamases and was rapidly lethal to susceptible bacteria. In Escherichia coli, GV104326 bound predominantly to PBPs 1a and 2 and at low concentrations osmotically stable round forms were observed. GV104326 showed an affinity for PBPs 2 and 4 of Staphylococcus aureus.

Multicenter evaluation of the in vitro activity of piperacillin-tazobactam compared with eleven selected beta-lactam antibiotics and ciprofloxacin against more than 42,000 aerobic gram-positive and gram-negative bacteria. In Vitro Susceptibility Surveillance Group

The in vitro activities of piperacillin-tazobactam, 11 other beta-lactam antibiotics, and ciprofloxacin were evaluated in a large multicenter study. A total of 42,208 organisms, collected from 79 listed medical centers and large community hospitals, were tested using the National Committee for Clinical Laboratory Standards broth microdilution procedure. Imipenem (94.7% inhibition), ciprofloxacin (93.8%), and ceftazidime (90.8%) were the most active antibiotics against 31,426 Gram-negative bacilli. Piperacillin-tazobactam (88.8%) and ticarcillin-clavulanate (86.4%) were the most active combination antibiotics against these organisms. Ampicillin-sulbactam (97.8%), piperacillin-tazobactam (96.4%), and imipenem (96.9%) were the most active antibiotics against 10,782 Gram-positive cocci. Overall, the most active antibiotics against all organisms tested were imipenem (95.2%), ciprofloxacin (91.0%), and piperacillin-tazobactam (90.8%).

Piperacillin/tazobactam. A review of its antibacterial activity, pharmacokinetic properties and therapeutic potential

Combining tazobactam, a beta-lactamase inhibitor, with the ureidopenicillin, piperacillin, successfully restores the activity of piperacillin against beta-lactamase-producing bacteria. Tazobactam has inhibitory activity, and therefore protects piperacillin against Richmond and Sykes types II, III, IV and V beta-lactamases, staphylococcal penicillinase and extended-spectrum beta-lactamases. However, tazobactam has only species-specific activity against class I chromosomally-mediated enzymes. Resistant organisms include some Citrobacter spp., Enterobacter spp., Serratia spp., Xanthomonas maltophilia and Enterococcus faecium. Consistent with its in vitro activity, preliminary clinical data indicate that the fixed combination of piperacillin/tazobactam (dose ratio 8:1) is effective in the treatment of moderate to severe polymicrobial infections, including intra-abdominal, skin and soft-tissue and lower respiratory tract infections. In limited comparative trials, piperacillin/tazobactam demonstrated equivalent or better efficacy than standard comparator regimens in these infections. Piperacillin/tazobactam in combination with an aminoglycoside was effective in the empirical treatment of fever in patients with neutropenia and compared favourably with ceftazidime in combination with an aminoglycoside, although second-line therapy with a glycopeptide antibiotic may be indicated in unresponsive episodes. Data from phase III trials indicate that piperacillin/tazobactam has a tolerability profile typical of a penicillin agent. Piperacillin/tazobactam provides a broad spectrum of antibacterial activity in a convenient single formulation suitable for use in the treatment of polymicrobial infections. Possible limitations concern its restricted activity against class I beta-lactamases, enzymes that are becoming increasingly important in the nosocomial environment. Combined therapy with an aminoglycoside may be necessary in more serious infections.

Synthesis and beta-lactamase inhibitory activity of 6-fluoropenicillanic acids

The benzyl 6-fluoro-penicillanate sulfides 4a, 6a, 7a; and sulfones 6c, 7d were synthesized. The conversion to their free acids 4b, 6b, 6d, 7b, 7e and potassium salts 7c, 7f are described. These acids and salt 7c were evaluated as beta-lactamase inhibitors using beta-lactamase I from Bacillus cereus. The data indicate that substitution of the 6 alpha-hydrogen by a 6 alpha-fluorine atom on 6 beta-bromopenicillanic acid (1), leads to loss of beta-lactamase inhibitory activity. In the case of the isomers 6 beta- and 6 alpha-fluoropenicillanic acids the 6 beta-enantiomer proved to be considerably more potent. Potassium salts of 6 beta-fluoropenicillanate sulfide and sulfone were unstable in solid state and in water solution. The fragmentation of the sulfone in two parts in water solution is consistent with the hydrolytic behavior to the penicillanic acid sulfone (2) with 0.5 N NaOH.

Effects of antibiotic treatment on clinical conditions and bacterial growth with guided tissue regeneration

Mucogingival flaps were reflected over pairs of mandibular molar teeth with Class II furcation invasions. The dimensions of the furcations were measured. The teeth were debrided and an expanded polytetrafluoroethylene (e-PTFE) membrane was placed and retained over one furcation of each pair (test site) for 4 weeks. The second site served as a control. Eight patients (group 1) with 12 e-PTFE sites received no antibiotic. Seven patients (group 2) with 12 e-PTFE sites were administered amoxicillin/clavulanate potassium for 10 days. Paper-points were used to collect bacterial samples and clinical indices were recorded at baseline and weekly for 4 weeks. Paper-point samples and the e-PTFE collected at week 4 were sonicated and analyzed by DNA probes for seven putative pathogens. At baseline no parameter showed statistical differences between groups or sites. At week 1 significantly greater levels of Prevotella intermedia type I (P < 0.05) and Fusobacterium nucleatum (P < 0.01) were found in group 1. At week 4, paper-point samples from test sites (P < 0.05) and e-PTFE materials (P < 0.001) showed significantly higher presence of Bacteroides forsythus in group 1. No significant microbial changes were found for control sites over time or between groups. The total bacterial load at test sites over time increased similarly for patients administered or not administered the antibiotic. Clinical signs of inflammation were significantly greater in group 1 and associated with the presence of B. forsythus (P < 0.01).

Comparison of ampicillin/sulbactam and amoxicillin/clavulanic acid for detection of borderline oxacillin-resistant Staphylococcus aureus

Borderline oxacillin-resistant Staphylococcus aureus (BORSA) may be misidentified as intrinsically methicillin-resistant Staphylococcus aureus (MRSA) in the clinical laboratory. Under disk diffusion testing conditions designed to maximize detection of MRSA (incubation at 32 degrees C, pre-induction with methicillin, or plating on 4% NaCl-supplemented agar), BORSA strains also tend to appear resistant to semisynthetic penicillins. Under these conditions, ampicillin/sulbactam appears to be more accurate than amoxicillin/clavulanic acid for differentiating BORSA from MRSA.

Antibacterial activity of cefoperazone and cefoperazone plus sulbactam in a neutropenic site model

Efficacy of cefoperazone versus cefoperazone plus sulbactam was studied in a rabbit neutropenic site infection model against a broad range of clinical isolates including six isolates each of staphylococci, enterococci, pneumococci, Enterobacteriaceae, and Pseudomonas aeruginosa. Therapy of cefoperazone plus sulbactam demonstrated enhanced efficacy against the staphylococci, pseudomonads, and Enterobacteriaceae. The activity of cefoperazone against enterococci and pneumococci was not enhanced or inhibited by the addition of sulbactam. Increased concentrations of cefoperazone found at the infection sites when sulbactam was added to the therapeutic regimen indicates that sulbactam provided a protection to cefoperazone from beta-lactamases produced by staphylococci and Enterobacteriaceae. The combination improved the efficacy of cefoperazone in this animal model.

The role of penicillin amidases in nature and in industry

Penicillin amidase (PA) is the enzyme used commercially for the production of semisynthetic penicillins. During the past decade, a detailed picture of the structure and regulation of the gene encoding this enzyme has emerged, revealing a variety of interesting features that are unique among microorganisms. Clues to the biological role of this enzyme have been provided, as well as new strategies for the commercial production and utilization of PA.

Ceftriaxone-sulbactam combination in rabbit endocarditis caused by a strain of Klebsiella pneumoniae producing extended-broad-spectrum TEM-3 beta-lactamase

We studied the activity of the combination of sulbactam and ceftriaxone against a Klebsiella pneumoniae strain producing TEM-3, a new extended-broad-spectrum beta-lactamase, in an endocarditis model. In vitro, ceftriaxone was strongly inactivated in the presence of TEM-3 (MBC, 128 micrograms/ml with an inoculum of 5 x 10(5) CFU/ml). A marked inoculum effect was demonstrated with sulbactam: effective concentrations of inhibitor needed to reduce the MIC and MBC of ceftriaxone to similar levels increased from 1 microgram/ml in the presence of an inoculum of 5 x 10(5) CFU/ml to 20 micrograms/ml in the presence of an inoculum of 1 x 10(7) CFU/ml. In vivo, sulbactam given at 200 mg/kg of body weight every 12 h, a dosage higher than that previously reported to be effective against rabbit endocarditis caused by other microorganisms, was not sufficient to restore the complete activity of ceftriaxone given at 30 mg/kg once daily for 4 days. This insufficient activity may be correlated with the presence of a high level of beta-lactamase inside the vegetations, as indicated by a quantitative in vitro assay of beta-lactamase activity in the cardiac vegetation, suggesting an insufficient inactivation of the extended-broad-spectrum beta-lactamase in vivo.

In vitro activities of ampicillin-sulbactam and cefoperazone-sulbactam against oxacillin-susceptible and oxacillin-resistant staphylococci

Ampicillin-sulbactam and cefoperazone-sulbactam were tested against staphylococci that were collected from 40 different medical centers throughout the United States. Oxacillin-resistant strains were resistant to both drug combinations, but oxacillin-susceptible strains were uniformly susceptible. The latter included strains with borderline susceptibility to oxacillin and methicillin.

Antistaphylococcal activity of amoxicillin and ticarcillin when combined with clavulanic acid. Evaluation of oxacillin-resistant and oxacillin-susceptible isolates

The beta-lactamase inhibitor, clavulanic acid, was combined with amoxicillin and with ticarcillin for in vitro studies with 586 staphylococci: 97 stock cultures of oxacillin-resistant strains recovered before 1982, and 489 blood or wound isolates collected from 40 separate medical centers during 1987-1988 (300 were oxacillin resistant). Over 92% of the staphylococci produced beta-lactamase enzymes and were thus resistant to both penicillins. However, with the addition of clavulanic acid, oxacillin-susceptible strains were rendered susceptible to low concentrations of amoxicillin and ticarcillin. Staphylococcus aureus strains with borderline or partial borderline resistance to penicillinase-resistant penicillins occurred infrequently (72 of 325 S. aureus isolates). Those strains were susceptible to both clavulanic acid combinations, because their methicillin resistance is thought to be due to an excess beta-lactamase production. Strains with chromosomally mediated intrinsic heteroresistance were relatively resistant to both drug combinations. Minimal inhibitory concentration (MIC) breakpoints that best separated those heteroresistant strains from oxacillin-susceptible isolates were as follows: amoxicillin/clavulanic acid, less than or equal to 2.0/1.0 micrograms/ml for susceptible; and ticarcillin/clavulanic acid, less than or equal to 4.0/2.0 micrograms/ml for susceptible. When the broth was supplemented by 2% NaCl, MICs for both drug combinations were increased by less than one doubling dilution. Although oxacillin and methicillin broth microdilution tests were more reliable when 2% NaCl was added, tests with the two drug combinations were only minimally improved by adding 2% NaCl to the broth medium.

Comparative in vitro activity of cefoperazone and various combinations of cefoperazone/sulbactam

Cefoperazone with 2 and 4 micrograms/ml of sulbactam and in a 2:1 ratio was tested against 1258 clinical isolates of Gram-positive and Gram-negative bacteria, as well as against Gram-negative bacilli that had stably derepressed Type I beta-lactamase or that were hyperproductive of non-Type I beta-lactamases. The 2:1 cefoperazone/sulbactam combination was the most potent combination tested. With this combination cefoperazone minimum inhibitory concentrations (MICs) of 27 of 40 (67%) of the clinical isolates of Pseudomonas species and 64 of 67 (95%) of clinical isolates of the Enterobacteriaceae were reduced from greater than or equal to 64 micrograms/ml by at least two-fold. In contrast, cefoperazone MICs of greater than or equal to 64 micrograms/ml remained unchanged for 26 (65%) and 24 (60%) of Pseudomonas species and 35 (52%) and 30 (45%) of the Enterobacteriaceae in the presence of 2 and 4 micrograms/ml of sulbactam, respectively. Cefoperazone/sulbactam in the 2:1 ratio was also the most active combination against the mutants derepressed for Type I beta-lactamase. Although the 2:1 combination of cefoperazone/sulbactam had the greatest potency in vitro, it remains to be seen whether this combination is predictive of clinical outcome from treatment of cefoperazone-resistant Gram-negative bacilli with cefoperazone/sulbactam.

Activity of ticarcillin/clavulanate and piperacillin/tazobactam (YTR 830; CL-298,741) against clinical isolates and against mutants derepressed for class I beta-lactamase

Piperacillin/tazobactam (YTR 830; CL-298,741) was tested against fresh and stock clinical isolates of Gram-negative bacilli, as well as against Gram-negative bacilli that had stably derepressed Class I beta-lactamases or that were hyperproductive of non-Class I beta-lactamases. Of 63 clinical isolates of the Enterobacteriaceae with ticarcillin (plus clavulanate) minimum inhibitory concentrations (MICs) of greater than or equal to 128 micrograms/ml, 16 had piperacillin/tazobactam MICs of less than or equal to 16/2 micrograms/ml. Of 48 clinical isolates of Pseudomonas spp. with ticarcillin (plus clavulanate) MICs of greater than or equal to 128 micrograms/ml, 35 had piperacillin/tazobactam MICs of less than or equal to 64/8 micrograms/ml. Tazobactam generally reduced piperacillin MICs by two- to greater than or equal to eightfold against stably derepressed mutants for Class I beta-lactamases.

Current trends and new perspectives in antibiotic therapy

During the last ten years, limitless numbers of antimicrobials were produced by the pharmaceutical industry and some have been marketed. The main objectives of new drugs are to overcome the expanding problems of resistant bacteria, to fill the gaps of spectrum of previous agents. These objectives are progressively reached by new beta-lactams, penems, fluoroquinolones; in general practice, new oral cephalosporins are becoming available. To overcome toxicity problems new concepts in antibiotic usage such as intermittent aminoglycoside regimens are suggested. Research in antibiotics, the discovery of new molecules or the re-evaluation of older drugs constitute dynamic trends in antibiotic therapy.