Clinical microbiology and infection vol:vol. 14 pages:S1-S815
European Congress of Clinical Microbiology and Infectious Diseases (ECCMID) edition:18th location:Barcelona, Spain date:April 19-22th 2008
Objectives: Rapid detection of extended-spectrum beta-lactamase (ESBL) producing Enterobacteriaceae is crucial in order to control spread and institution of optimal antibiotic therapy. Purpose of this study was to compare the performance of different routine methods.
Methods: Isolates for this study were selected on basis of a positive ESBL-screen test and/or resistance to cefuroxime with the Vitek 2 system (cards N 045 and N 046).
Over a period of 6 weeks (March-April 2007) 254 isolates were consecutively recovered from 215 clinical specimens (urine 54.9%, sputum 19%, other 25.1% and blood 1%). The following species were included: E. coli (n=96), E. aerogenes (n=39), E. cloacae (n=34), K. oxytoca (n=15), K. pneumoniae (n=22) and M. morganii (n=48).
On all 254 isolates the disk approximation method with cefotaxime (30µg), ceftazidime (30µg), aztreonam (30µg) and amoxicillin-clavulanic acid (20/10) disks was used as reference method. Only 91 isolates were identified as ESBL producer. Routine performance of three different methods for ESBL detection was compared: the Vitek 2 system (Biomérieux, Marcy l’Etoile, France), E-test ESBL (AB BIODISK, Solna, Sweden; strips with ceftazidime and cefepime/clavulanic acid) and chrom IDTM ESBL (Biomérieux, Marcy l’Etoile, France). All analyses were performed in accordance with the guidelines of the manufacturer.
Results: The performance characteristics of the three methods are shown in the table.
The method with the highest sensitivity for the detection of ESBLs was the E-test (98.9%) followed by the Vitek 2 (97%), however specificity was more variable, ranging from 50.1% (Vitek 2) to 96.3% (E-test). The performance differed widely between the species investigated.
Conclusion: Considering the rather low specificity of the ESBL detection by Vitek 2 we recommend the use of confirmation for all organisms reported positive for ESBL production by Vitek 2.