Unexpected Tigecycline Resistance Among Acinetobacter baumannii Isolates: High Minor Error Rate by Etest

• Published in: Journal of chemotherapy (Florence) Vol. 21; no. 4; pp. 390 - 395
• Main Authors: Kulah, C., Celebi, G., Aktas, E., Mengeloglu, Z., Comert, F., Ankarali, H.
• Format: Journal Article
• Language: English
• Published: Firenze Taylor & Francis 01-08-2009; EIFT
• Subjects: Acinetobacter baumannii; Acinetobacter baumannii - drug effects; Acinetobacter baumannii - isolation & purification; Acinetobacter Infections - drug therapy; Acinetobacter Infections - microbiology; Anti-Bacterial Agents - pharmacology; Antibiotics. Antiinfectious agents. Antiparasitic agents; Biological and medical sciences; breakpoints; Diagnostic Errors - statistics & numerical data; Drug Resistance, Bacterial; Etest; Humans; Medical sciences; Microbial Sensitivity Tests; Minocycline - analogs & derivatives; Minocycline - pharmacology; Pharmacology. Drug treatments; Quality Control; resistance; susceptibility testing; Tigecycline; Glycylcycline derivatives; Breakpoint; susceptibility testing; Drug susceptibility test; Neisseriaceae; Error rate; Boundary value; Resistance; Acinetobacter baumannii; Antibiotic; Etest; Bacteria; Micrococcales; Isolate; breakpoints; Antibacterial agent; Tigecycline
• ISSN: 1120-009X; 1973-9478
• DOI: 10.1179/joc.2009.21.4.390

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? μg/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 ≥19/≤14 mm produced unacceptable minor errors while adjustment to ≥17/≤13 mm yielded the best results. In conclusion, resistance was not rare against our MDR A. baumanniiisolates although tigecycline had not been used previously. Breakpoints ≥17/≤13 mm may be preferred for DD. We suggest caution with intermediate results by Etest.