Cefditoren versus ceftazidime in inducer-substrate combinations for the evaluation of AmpC production in a disc approximation test.
OBJECTIVE
To evaluate cefditoren in inducer-substrate combinations to screen for AmpC induction.


METHODS
100 clinical isolates (25 P. aeruginosa, 25 E. cloacae, 14 M. morganii, 13 S. marcescens, 12 C. freundii, 7 P. rettgeri, and 4 E. aerogenes) were tested by the Kirby-Bauer disc approximation method using cefditoren and ceftazidime discs as substrates, and cefditoren and imipenem discs as inducers.


RESULTS
None of the strains showed induction of AmpC with cefditoren-ceftazidime as inducer-substrate combination. Imipenem-cefditoren as inducer-substrate combination was not useful for evaluating strains of P. aeruginosa since no inhibition zones surrounding the cefditoren disc were found. Among evaluable enterobacteria (those showing substrate inhibition zone), inducible Amp C was detected in 48 out of 63 (76.2%) with cefditoren, and in 33 out of 68 (48.5%) isolates with ceftazidime as substrate. Significantly (p=0.013) higher number of AmpC producers were detected with cefditoren versus ceftazidime (76.2% vs. 48.5%), due to the differences found for E. cloacae (72.8% vs. 21.7%; p=0.0009) and S. marcescens (100% vs. 54.5%; p=0.03). Higher mean reductions of diameters around substrate discs were found for cefditoren (4.17 mm) vs. ceftazidime (3.79 mm), reaching statistical significance (p<0.05) for indol-positive proteae: M. morganii (5.32 mm vs. 3.92 mm) and P. rettgeri (3.47 mm vs. 2.64 mm).


CONCLUSIONS
Cefditoren 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-ceftazidime combination, mainly for Enterobacter spp. and Serratia spp., with higher diameter reductions for indol-positive proteae.
Cafini
F
F
Microbiology Dpt, School of Medicine, Univ. Complutense, Avda. Complutense s/n, 28040 Madrid, Spain.
Aguilar
L
L
Alou
L
L
Giménez
M J
MJ
Sevillano
D
D
Torrico
M
M
González
N
N
Coronel
P
P
Prieto
J
J
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001419:Bacteria / Q000187:drug effects* / Q000235:genetics*; D001424:Bacterial Infections / Q000382:microbiology; D001426:Bacterial Proteins / Q000235:genetics*; D002442:Ceftazidime / Q000494:pharmacology*; D002511:Cephalosporins / Q000494:pharmacology*; D004755:Enterobacteriaceae / Q000187:drug effects; D006801:Humans; D015378:Imipenem / Q000494:pharmacology; D008826:Microbial Sensitivity Tests; D013045:Species Specificity; D001618:beta-Lactamases / Q000235:genetics*
D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D002511:Cephalosporins; D015378:Imipenem; C073460:cefditoren; D002442:Ceftazidime; C048795:AmpC beta-lactamases; D001618:beta-Lactamases