Detection of extended spectrum b-lactamases in Enterobacteriaceae strains using four different methods in a Tunisian paediatric hospital

Abstract number: p1454

Jlili  N.E., Smaoui  H., Rejiba  S., Kechrid  A.


The reliability of four phenotypic methods to detect extended-spectrum b-lactamases (ESBLs) was investigated in the present study.


A total of 55 non-duplicate clinical isolates of third generation cephalosporin-resistant Enterobacteriaceae species suspected of ESBL production were collected from January to September 2003. Medium and disc charge are used according to the CA-SFM guidelines. The isolates were screened for ESBL production by: (i) double-disk synergy test (DDST), (ii) modifying double-disk test (MDDT), performed with discs used in the DDST in addition to cefepime, aztreonam and piperacillin-tazobactam association, (iii) E-test ESBL (AB BIODISK) detection system, based on the reduction in the ceftazidime or cefotaxime MIC in the presence of clavulanic acid, and (iv) Cica- b test I/MBL (Kanto Chemical Co.Inc.) using the chromogenic cephalosporin HMRZ-86, which reacts ESBL directly and changing the colour rapidly.


Among 55 strains (39 Klebsiella pneumoniae, 4 Escherichia coli, 6 Enterbater cloacae and 5 Enterobacter aerogenes) studied, the classic DDST based clavulanate synergy classified only 36 (56.4%) ESBL positive, while, the MDDT detected the presence of ESBL in 47 (85.4%). Negative synergy affected all the species with DDST, whereas negative synergy spared the totality of K. pneumoniae with MDDT. Results of the E-test ESBL confirmed the ESBL production in 44 (80%) among the 47 ESBL producers screened by MDDT. The results of the E-test were indeterminate for the other eleven clinical isolates. The chromogenic test gave the highest ESBL detection rates with 52 (94.5%) strains. According to the study, the sensitivity and specificity of the HMRZ-86 for detecting ESBLs seemed to be the better. The combination of all ESBL detection methods showed agreement for 35 ESBL positive (32 K. pneumoniae, 3 E. aerogenes) and 3 ESBL negative clinical isolates, that belong to third bacterial group. At least, one method yielded a discordant result for each of the remaining 17 isolates.


Excepted the DDST, all the other methods conferred good rates to detect ESBL production. Chromogenic test seems to be potential and suitable tool to ESBL screening and it must be valuable in clinical laboratory.

Session Details

Date: 01/08/2007
Time: 00:00-00:00
Session name: XXIst ISTH Congress
Location: Oxford, UK
Presentation type:
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