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Comparison of 4 commercial methods for antimicrobial susceptibility testing of temocillin

Abstract number: R2411

Rodriguez-Villalobos H., Cardentey-Reyes A., Thiroux C., Nonhoff C., Struelens M.J.

Objectives: Susceptibility testing for temocillin is currently performed by disk diffusion method (DD). E-test (AB Biodisk) and new VITEK 2 (VT) cards (bioMérieux) have been recently marketed for temocillin testing. Data concerning the accuracy of these commercial methods are limited. The aim of this study was to compare the accuracy of the VT, E-test and DD methods (paper disk from Beckton Dickinson and Neo-Sensitabs from Rosco) for determining susceptibility of Escherichia coli to temocillin.

Methods: We tested 153 E. coli clinical isolates, including ESBL-producing strains (54%): 70 CTX-M (CTX-M-2, CTX-M-9, CTX-M-15), 12 TEM (TEM-24, TEM-30, TEM-52), 6 SHV-12, 15 AmpC hyper-producers (AmpC HP) and 53 strains with wild phenotype or other resistance mechanisms. ESBL production was confirmed by combined disk method (Bio Rad), PCR and DNA sequencing. Strains were tested in parallel by VT (AST-N045 and AST-N046 cards), DD, E-test and agar dilution (AD) according to the CLSI guidelines as gold standard method.

Results: MICs obtained by E-test and VT were within 1 dilution of those obtained by AD in >99% of isolates. No differences were observed between AD, E-test and VT (p > 0.5). VT and E-test showed the lowest number of discrepancies (TABLE).

Table. Summary of results. Results interpretation based on breakpoints from Fuchs (MIC leqslant R: less-than-or-eq, slant 16 mg/L)

VT provided results in a mean time of 7 hours (6–10 hours). Errors were observed with isolates showing borderline temocillin MIC of 16 or 32 mg/L. No discrepancies were observed for strains with MIC < 4 mg/L.

Conclusion: E-test and the VITEK 2 system showed good accuracy for determination of MICs of temocillin in E. coli including ESBL and AmpC HP strains. For disk diffusion Neo-Sensitabs showed better discrimination between susceptible and resistant strains and lower number of discrepancies than BD disks.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Subject:
Location: Barcelona, Spain
Presentation type:
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