Unexpected tigecycline resistance among Acinetobacter baumannii Isolates: high minor error rate by Etest.
Tigecycline seems to be a promising agent for treatment of resistant Acinetobacter baumannii infections, however approved criteria for susceptibility testing are still lacking. The aim of this study was to evaluate tigecycline activity against multidrug resistant A. baumannii clinical isolates, as well as susceptibility testing methods and disk diffusion (DD) breakpoints. Reference broth microdilution (BMD), Etest and DD methods were used. MIC(50 )and MIC(90 )by the reference method were 1 and 8 microg/ml, respectively. Applying the breakpoints for enterobactericeae, 85.7% of the isolates were sensitive to tigecycline. The Etest resulted in lower susceptibility rates (63.7%). Essential agreement between Etest and BMD was 75.8%. 21.9% of the strains were susceptible by BMD and intermediate by Etest. Provisional DD breakpoints >or=19/<or=14 mm produced unacceptable minor errors while adjustment to >or=17/<or=13 mm yielded the best results. In conclusion, resistance was not rare against our MDR A. baumannii isolates although tigecycline had not been used previously. Breakpoints >or=17/<or=13 mm may be preferred for DD. We suggest caution with intermediate results by Etest.
Kulah
C
C
Department of Medical Microbiology and Clinical Microbiology, Faculty of Medicine, Zonguldak Karaelmas University, Zonguldak, Turkey. canankulah@yahoo.com
Celebi
G
G
Aktas
E
E
Mengeloglu
Z
Z
Comert
F
F
Ankarali
H
H
D000151:Acinetobacter Infections / Q000188:drug therapy / Q000382:microbiology*; D040981:Acinetobacter baumannii / Q000187:drug effects* / Q000302:isolation & purification; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D003951:Diagnostic Errors / Q000706:statistics & numerical data*; D024881:Drug Resistance, Bacterial; D006801:Humans; D008826:Microbial Sensitivity Tests; D008911:Minocycline / Q000031:analogs & derivatives* / Q000494:pharmacology; D011786:Quality Control; D000078304:Tigecycline
D000900:Anti-Bacterial Agents; D000078304:Tigecycline; D008911:Minocycline