Inhibitor resistant class A β-lactamases
Geriatric CARE Center, Cleveland, OH 44120, USA.Frontiers in Bioscience (Impact Factor: 3.52). 06/1999; 4(1-3):e34-41. DOI: 10.2741/Bonomo
Beta-lactamase inhibitors (clavulanic acid, tazobactam, and sulbactam) greatly enhance the therapeutic efficacy of their partner antibiotics (amoxacillin, ampicillin, piperacillin, and ticarcillin) against common enteric and non-enteric organisms possessing class A beta-lactamases. Unfortunately, the number of class A enzymes being discovered that are resistant to these combinations is increasingly rapidly. The TEM and SHV class A beta-lactamases resistant to inhibitors have point mutations in critical amino acids important for catalysis. Compared to the wild type beta-lactamase, inhibitor resistant enzymes are inefficient at hydrolyzing benzylpenicillin, aminopenicillins, and cephalosporins. Nevertheless, hyper-production of these enzymes resulting from mutations in the promoter region can confer substantial levels of resistance. Understanding the microbiologic and kinetic properties of these inhibitor resistant class A beta-lactamases can lead to the design of more potent beta-lactam compounds as well as more effective inhibitors.
- [Show abstract] [Hide abstract]
ABSTRACT: beta-Lactamase inhibitor:beta-lactam combinations remain one of the most successful strategies for the treatment of bacterial infections. Over the last 20 years the number and diversity of serine and metallo active site beta-lactamases has increased dramatically. This review highlights some of the new additions to the beta-lactamase arena and discusses how the commercially available beta-lactamase inhibitors are keeping pace with the changing epidemiology of beta-lactamases. In addition, we survey the progress with the design of novel inhibitors of serine and metallo-beta-lactamases. Focus is given to the recent advances in the design of metallo-beta-lactamase inhibitors as these enzymes pose a serious emerging threat to the use of all beta-lactam based therapies.
- [Show abstract] [Hide abstract]
ABSTRACT: Extended-spectrum beta-lactamases (ESBLs) are enzymes found in gram-negative bacilli that mediate resistance to extended-spectrum cephalosporins and aztreonam. In 1999, the National Committee for Clinical Laboratory Standards (NCCLS) published methods for screening and confirming the presence of ESBLs in Klebsiella pneumoniae, Klebsiella oxytoca, and Escherichia coli. To evaluate the confirmation protocol, we tested 139 isolates of K. pneumoniae that were sent to Project ICARE (Intensive Care Antimicrobial Resistance Epidemiology) from 19 hospitals in 11 U.S. states. Each isolate met the NCCLS screening criteria for potential ESBL producers (ceftazidime [CAZ] or cefotaxime [CTX] MICs were > or =2 microg/ml for all isolates). Initially, 117 (84%) isolates demonstrated a clavulanic acid (CA) effect by disk diffusion (i.e., an increase in CAZ or CTX zone diameters of > or =5 mm in the presence of CA), and 114 (82%) demonstrated a CA effect by broth microdilution (reduction of CAZ or CTX MICs by > or =3 dilutions). For five isolates, a CA effect could not be determined initially by broth microdilution because of off-scale CAZ results. However, a CA effect was observed in two of these isolates by testing cefepime and cefepime plus CA. The cefoxitin MICs for 23 isolates that failed to show a CA effect by broth microdilution were > or =32 microg/ml, suggesting either the presence of an AmpC-type beta-lactamase or porin changes that could mask a CA effect. By isoelectric focusing (IEF), 7 of the 23 isolates contained a beta-lactamase with a pI of > or =8.3 suggestive of an AmpC-type beta-lactamase; 6 of the 7 isolates were shown by PCR to contain both ampC-type and bla(OXA) genes. The IEF profiles of the remaining 16 isolates showed a variety of beta-lactamase bands, all of which had pIs of < or =7.5. All 16 isolates were negative by PCR with multiple primer sets for ampC-type, bla(OXA), and bla(CTX-M) genes. In summary, 83.5% of the K. pneumoniae isolates that were identified initially as presumptive ESBL producers were positive for a CA effect, while 5.0% contained beta-lactamases that likely masked the CA effect. The remaining 11.5% of the isolates studied contained beta-lactamases that did not demonstrate a CA effect. An algorithm based on phenotypic analyses is suggested for evaluation of such isolates.
- [Show abstract] [Hide abstract]
ABSTRACT: TEM-, SHV-, and OXA-type beta-lactamases were studied by PCR with 124 ampicillin-resistant (AMP(r)) Escherichia coli isolates recovered from foods of animal origin (n = 20) and feces of humans (n = 49) and healthy animals (n = 55). PCR showed that 103 isolates were positive for TEM and negative for SHV and OXA. Three E. coli isolates showed a positive reaction for OXA, and one showed a positive reaction for SHV. The remaining 17 E. coli isolates were negative for the three enzymes by PCR. Fifty-seven of the 103 bla(TEM) amplicons were sequenced. Different molecular variants of bla(TEM-1) were found in 52 isolates: bla(TEM-1a) (n = 9), bla(TEM-1b) (n = 36), bla(TEM-1c) (n = 6), and bla(TEM-1f) (n = 1). Four inhibitor-resistant TEM (IRT) beta-lactamase-encoding genes were also detected: bla(TEM-30c) (IRT-2), bla(TEM-34b) (IRT-6), bla(TEM-40b) (IRT-11), and bla(TEM-51a) (IRT-15). A new bla(TEM) gene, named bla(TEM-95b), which showed a mutation in amino acid 145 (P-->A) was detected. It was found in a food isolate of chicken origin (AMP(r), amoxicillin-clavulanic acid susceptible). The promoter region in 24 bla(TEM) amplicons was analyzed, and the weak P3 promoter was found in 23 of them (bla(TEM-1) in 20 amplicons and bla(TEM-51a), bla(TEM-30c), and bla(TEM-95b) in 1 amplicon each). The strong Pa/Pb promoter was found only in the bla(TEM-34b) gene. No extended-spectrum beta-lactamases were detected. Mutations at position -42 or -32 in the ampC gene promoter were demonstrated in 4 of 10 E. coli isolates for which the cefoxitin MIC was >/=16 micro g/ml. Different variants of bla(TEM-1) and IRT bla(TEM) genes were found among the AMP(r) E. coli isolates from foods and the feces of humans and healthy animals, and a new gene, bla(TEM-95b) (P3), was detected.
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.