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Detection of low-level resistance to carbapenems using the VITEK 2 and the advanced expert system

Abstract number: 1733_1142

Afkou Z., Kontopoulou K., Sofianou D., Tsivitanidou M.

Objectives: Metallo-b-lactamases (MBLs) are plasmid mediated ß-lactamases conferring resistance to all ß-lactams except aztreonam. These acquired MBLs recently have been spread among Enterobacteriaceae. Many of enterobacteria, possessing MBL genes exhibit low-level resistance to carbapenems or appear susceptible by the routine techniques and pass unnoticed in most cases. Our objective was the evaluation of VITEK 2 automated system to detect low-level resistance to carbapenems.

Methods: A total of 33 Enterobacteriaceae isolates (2 Escherichia coli, 9 Enterobacter cloacae, 22 Klebsiella pneumoniae) recovered from clinical specimens at Hippocration General Hospital were studied. The identification and susceptibility testing were performed by using the VITEK 2 automated system (bioMérieux, France).

All isolates resistant to ceftazidime, cefoxitin and cefotaxime were characterised as resistant or intermediate to imipenem (IMP) by the automated system. The strains were tested by disk-diffusion method according to CLSI breakpoint criteria. IMP-EDTA double disk synergy test was carried out to screen the production of MBL. Molecular investigation was used to confirm the presence of plasmid-mediated MBL.

Results: By the VITEK 2 automated system 18 isolates (54.5%) were characterised as intermediate to imipenem (MIC = 8 mg/mL) while the remaining 15 (45.5%) were resistant (MIC > 16). By the disk diffusion method 1 isolate (3%) was intermediate (diameter 14–15 mm), 9 strains (27.2%) were resistant (diameter ≤13 mm) and 23 strains (69.8%) were susceptible (diameter >16 mm). Double disk synergy test using an imipenem disk and an EDTA disk was positive in all strains

indicating the MBL production. Additionally, all isolates were positive in PCR assays with blavim specific oligonucleotides.

Conclusions: This study demonstrated the capacity of VITEK 2 to detect low-level resistance to carbapenems. This automated system combined with EDTA synergy test is able to detect MBL producers in clinical laboratories. The early detection of MBLs permits the selection of appropriate treatment and the implementation of strict infection control measures in order to prevent their spread in the hospital.

Session Details

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