Article

Inhibitor resistant class A beta-lactamases.

Geriatric CARE Center, Cleveland, OH 44120, USA.
Frontiers in Bioscience (Impact Factor: 4.25). 06/1999; 4:e34-41. DOI: 10.2741/Bonomo
Source: PubMed

ABSTRACT 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.

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    ABSTRACT: TEM-, SHV-, and OXA-type β-lactamases were studied by PCR with 124 ampicillin-resistant (AMPr) 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 blaTEM amplicons were sequenced. Different molecular variants of blaTEM-1 were found in 52 isolates: blaTEM-1a (n = 9), blaTEM-1b (n = 36), blaTEM-1c (n = 6), and blaTEM-1f (n = 1). Four inhibitor-resistant TEM (IRT) β-lactamase-encoding genes were also detected: blaTEM-30c (IRT-2), blaTEM-34b (IRT-6), blaTEM-40b (IRT-11), and blaTEM-51a (IRT-15). A new blaTEM gene, named blaTEM-95b, which showed a mutation in amino acid 145 (P→A) was detected. It was found in a food isolate of chicken origin (AMPr, amoxicillin-clavulanic acid susceptible). The promoter region in 24 blaTEM amplicons was analyzed, and the weak P3 promoter was found in 23 of them (blaTEM-1 in 20 amplicons and blaTEM-51a, blaTEM-30c, and blaTEM-95b in 1 amplicon each). The strong Pa/Pb promoter was found only in the blaTEM-34b gene. No extended-spectrum β-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 μg/ml. Different variants of blaTEM-1 and IRT blaTEM genes were found among the AMPr E. coli isolates from foods and the feces of humans and healthy animals, and a new gene, blaTEM-95b (P3), was detected.
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