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Cefditoren versus ceftazidime in inducer-substrate combinations for the evaluation of AmpC production in a disk approximation test

Abstract number: P2067

Cafini F., Aguilar L., Alou L., Gimenez M.J., Sevillano D., Torrico M., Gonzalez N., Coronel P., Prieto J.

Objective: To evaluate cefditoren (CDN) in inducer-substrate combinations to screen for AmpC induction.

Methods: 100 clinical isolates (25 Pseudomonas aeruginosa, 25 Enterobacter cloacae, 14 Morganella morganii, 13 Serratia marcescens, 12 Citrobacter freundii, 7 Providencia rettgeri, and 4 Enterobacter aerogenes) were tested by the Kirby-Bauer disc approximation method using CDN and ceftazidime (CAZ) discs as substrates, and CDN and imipenem discs as inducers. Photographs of the incubated plates were taken using visualisation Gel Doc and inhibition zones were measured using the ImageJ program. A positive induction was considered when the inhibition zone of the substrate disc was reduced by geqslant R: gt-or-equal, slanted2 mm. Comparisons of percentages of AmpC isolates detected with the different substrates were performed with the Fisher's exact test, and reductions in diameters were compared by the Student's t-test. A p < 0.05 was considered significant.

Results: None of the strains showed induction of AmpC with CDN-CAZ as inducer-substrate combination. Imipenem-CDN as inducer-substrate combination was not useful for evaluating strains of P. aeruginosa since no inhibition zones surrounding the cefditoren disc were found. Number (%) strains showing reduction when using CDN and CAZ as substrate, and mean±SD reduction in the inhibitory zone for valuable strains (those showing inhibitory zone) among the enteric bacteria tested, are shown in the Table.

Conclusion: CDN showed no induction capability, and when used as substrate (with imipenem as inducer) it offered detection rates of AmpC inducible enterobacteria higher than the imipenem-CAZ combination, mainly for Enterobacter spp. and Serratia spp., with higher diameter reductions for indol-positive proteae.

 CDN 10 mgCAZ 30 mg
 nNo. (%) of strains with reductionReduction (mm)nNo. (%) of strains with reductionReduction (mm)
C. freundii76 (85.7)5.16±2.37107 (70.0)4.94±2.98
M. morganii1310 (76.9)5.32±1.11a1311 (84.6)3.92±1.59
P. rettgeri73 (42.9)3.47±0.25a72 (28.6)2.64±0.02
S. marcescens1111 (100.0)b3.50±0.93116 (54.5)2.78±0.95
E. cloacae2216 (72.8)b4.19±1.00235 (21.7)3.88±2.39
E. aerogenes32 (66.6)3.45±0.9742 (50.0)2.76±0.03
Total6348 (76.2)b4.17±1.416833 (48.5)3.79±2.02
aSignificantly (p < 0.05) higher reduction than CAZ.
bSignificantly (p < 0.05) higher percentage of AmpC strains detected with CDN vs. CAZ.

Session Details

Date: 16/05/2009
Time: 00:00-00:00
Session name: 19th European Congress of Clinical Microbiology and Infectious Diseases
Subject:
Location: Helsinki, Finland, 16 - 19 May 2009
Presentation type:
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