Extended-spectrum b-lactamase producing Enterobacteriaceae in a Swiss university hospital: molecular characterisation and susceptibility to ertapenem

Abstract number: 1733_530

Bruderer T., Widmer A.F., Flury M., Oezcan S., Jutzi M., Frei R.

Objectives: First, to determine the molecular types of extended-spectrum b-lactamases (ESBLs) in Enterobacteriaceae at the University Hospital Basel, Switzerland. Secondly, to assess the activity of ertapenem against ESBL-producing strains.

Methods: Between 1/1/2003 and 31/12/2005, all consecutive clinical Enterobacteriaceae isolates were screened by use of 4 ESBL markers (ceftazidime, ceftriaxone, cefpodoxime, and aztreonam) according to Clinical and Laboratory Standards Institute (CLSI) guidelines. As phenotypic confirmatory test, three different ESBL Etest strips (AB Biodisk, Sweden) were used, i.e., ceftazidime, cefotaxime, and cefepime, each with and without clavulanic acid. Repetitive patient isolates and K1 hyperproducing Klebsiella oxytoca were excluded. To determine the molecular types, PCR amplifying SHV, TEM, and CTX-M genes was performed and amplicons were sequenced. Minimal inhibitory concentrations (MICs) of ertapenem were determined by Etest and interpreted according to the standards of CLSI.

Results: Among 8,384 isolates screened, 57 (0.68%) phenotypically confirmed ESBLs were identified. The ESBL rate was 1.1% and 3.4% in Escherichia coli and Klebsiella pneumoniae, respectively. Among ESBL strains, 59.6% were E. coli, 31.6% K. pneumoniae, and 8.8% other genera. The majority (49.1%) of ESBL strains was found in urine samples. PCR and DNA sequencing analysis demonstrated that 61.4% of the ESBL strains expressed a CTX-M type, 15.8% an SHV ESBL type, and 5.3% a TEM ESBL type. CTX-M-15 was the predominant (29.8%) b-lactamase followed by CTX-M-3 and SHV-12. There was no epidemiological and microbiological evidence for an outbreak situation. In 9 strains, no CTX-M, SHV or TEM ESBL could be detected. The MIC50 and MIC90 of ertapenem were 0.06 mg/l and 0.25 mg/l, respectively. Overall, 98.2% of the strains were susceptible to ertapenem (MIC ≤ 2 mg/l).

Conclusions: Despite an extensive screening strategy, the prevalence of ESBLs is low in our medical institution. The distribution of the ESBL types is similar to the distribution in institutions with high ESBL prevalence, being CTX-M the predominant ESBL class. The new compound ertapenem is highly active against the ESBL-producing Enterobacteriaceae tested.

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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