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Does high level production of SHV-type penicillinase confer resistance to ceftazidime in Enterobacteriaceae?
A Petit1, H Ben Yaghlane-Bouslama, L Sofer
1Muséum National d'Histoire Naturelle, URA 401 CNRS, Paris, France.
Abstract:
We report the isolation of a clinical isolate of Klebsiella pneumoniae that showed resistance to ceftazidime (MIC: 8 micrograms/ml), susceptibility to aztreonam (MIC: 2 micrograms/ml) and cefotaxime (MIC: 0.015 micrograms/ml). A synergistic effect between clavulanic acid and ceftazidime or aztreonam against this strain was also observed. The strain hyperproduced SHV-1 penicillinase (990 U/g) which is encoded by a self-transferrable plasmid of at least 150 kb. That the ceftazidime-resistance phenotype could be due to hyperproduction of SHV-1 penicillinase is supported by the study of a spontaneous ceftazidime-resistant mutant in vitro obtained from an Escherichia coli strain containing plasmid p453 encoding the SHV-1. Indeed, this mutant hyperproducing SHV-1 (2200 U/g) was resistant to ceftazidime (MIC: 16 micrograms/ml) and aztreonam (MIC: 8 micrograms/ml) but susceptible to cefotaxime (MIC: 0.03 ng/ml). Clavulanic acid showed a synergistic effect when associated with ceftazidime or aztreonam. In contrast, the hyperproduction of TEM-1 (790 U/g) did not confer a ceftazidime- and aztreonam-resistant phenotype while hyperproduction of both TEM-1 and SHV-1 increased the resistance to amoxycillin/clavulanic acid and to cephalothin.
Insights
A Klebsiella pneumoniae strain resistant to ceftazidime hyperproduced SHV-1 penicillinase. This resistance was linked to SHV-1, with clavulanic acid showing synergistic effects against the resistant bacteria.
Area of Science:
- Microbiology
- Molecular Biology
- Antimicrobial Resistance
Background:
- Klebsiella pneumoniae is a significant opportunistic pathogen.
- Antimicrobial resistance, particularly to beta-lactam antibiotics, is a growing global health concern.
- Beta-lactamases, such as SHV-1 and TEM-1, are key enzymes mediating resistance.
Purpose of the Study:
- To investigate the mechanism of ceftazidime resistance in a clinical isolate of Klebsiella pneumoniae.
- To determine the role of SHV-1 penicillinase hyperproduction in conferring resistance.
- To evaluate the synergistic effect of clavulanic acid with beta-lactam antibiotics.
Main Methods:
- Isolation and characterization of a clinical Klebsiella pneumoniae strain.
- Determination of antibiotic minimum inhibitory concentrations (MICs).
- Enzyme activity assays for penicillinase production.
- Plasmid analysis and transferability studies.
- In vitro mutagenesis to generate resistant mutants.
Main Results:
- The clinical isolate exhibited resistance to ceftazidime but susceptibility to aztreonam and cefotaxime.
- The strain hyperproduced SHV-1 penicillinase, encoded by a self-transferrable plasmid.
- A spontaneous mutant overproducing SHV-1 also showed ceftazidime and aztreonam resistance.
- Clavulanic acid demonstrated a synergistic effect with ceftazidime and aztreonam against the resistant strains.
- TEM-1 hyperproduction alone did not confer ceftazidime resistance.
Conclusions:
- Hyperproduction of SHV-1 penicillinase is a significant mechanism for ceftazidime resistance in Klebsiella pneumoniae.
- The presence of a self-transferrable plasmid carrying the SHV-1 gene facilitates the spread of resistance.
- Clavulanic acid can restore susceptibility to beta-lactam antibiotics in strains with SHV-1 hyperproduction.