Carbapenem resistance of Escherichia coli strains

Abstract number: 1734_15

Schaumann R., Adler D., Rodloff A.C.

Objectives: Carbapenem (CP) resistance of Escherichia coli strains is extremely rare and seldomly discussed. The aim of the present study was to investigate the resistance mechanisms of three recent clinical E. coli isolates that were CP resistant.

Methods: MICs for imipenem (IMP), meropenem (MER), and ertapenem (ERT) as well as ESBL or MBL production were determined by Etest. Furthermore, the three strains were analysed for blaTEM, blaSHV, blaampC, blaACC, blaVIM, and blaIMP by PCR and isoelectric focusing and visualisation by nitrocefin and coomassie blue was carried out. In addition, the strains were serially passaged on antibiotic free columbia agar plates and MICs re-determined. Conversely the three strains and – for control purposes – eight susceptible E. coli strains were incubated on solid media containing IMP, MER, and ERT, respectively, at twice their MICs. After incubation growing bacteria were harvested and incubated at four times MICs. This procedure was repeated with increasing antibiotic concentrations. The resulting MICs were confirmed by Etest.

Results: The MICs for the three resistant strains ranged from 4 to >32 mg/L. The other E. coli strains showed MICs between 0.004 and 0.38 mg/L. After passages on antibiotic free medium, the MICs for the three strains decreased to 0.38 to 16 mg/L. However, after passages on antibiotic containing agar plates the MICs were >32 mg/L for all three CPs tested. The resistant strains contained blaampC and blaTEM. Isoelectric focusing demonstrated b-lactamases of various isoelectric points while the MBL and ESBL tests were negative or not calculable except for one strain. Furthermore, elevated MICs were inducible with ERT and IMP in the susceptible strains but not with MER.

Conclusion:E. coli strains may posses various mechanisms such as blaampC and blaTEM that in combination cause CP resistance. They may loose their phenotypic resistance after several passages on antibiotic free medium. Conversely, employing passages on antibiotic containing medium led to reappearance of the resistant phenotype.

Session Details

Date: 31/03/2007
Time: 00:00-00:00
Session name: European Society of Clinical Microbiology and Infectious Diseases
Location: ICC, Munich, Germany
Presentation type:
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