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Ann Med Res. 2011; 18(4): 257-262

Evaluation of Tigecycline Susceptibility by Disk Diffusion, E-test and Broth Microdilution Methods in 30 Multidrug Resistant or Extreme Drug Resistant Acinetobacter Isolates


Ahmet Mansur*, Çiğdem Kuzucu*, Yasemin Ersoy**, Funda Yetkin**





Acinetobacter spp. are primarily associated with nosocomial infections and these isolates resistant to most antimicrobial agents. The present study was conducted to evaluate the in vitro susceptibility of tigecyline in multi-drug-resistant (MDR) and extreme-drug resistance (XDR) Acinetobacter strains by three different methods. MDR Acinetobacter isolates described in the study were resistant to at least three of the following antibiotics: imipenem, meropenem, ceftazidime, cefepime, aztreonam, piperacillin tazobactam, ciprofloxacin, tetracycline, ampicillin-sulbactam, trimethoprim-sulfamethoxazole, amikacin, gentamicin and tobramycin. XDR was defined as resistance to all above antibiotics excluding colistin and tigecyline. Identification of Acinetobacter spp. were made conventional methods. Antibiotic susceptibility tests were performed according to the criteria of Clinical and Laboratory Standards Institute (CLSI). All of the isolates were found resistant to carbapenem.

Disk diffusion, E-test and broth microdilution methods were used to evaluate the in vitro susceptibility of tigecyline. No tigecycline interpretative criteria universally accepted for Acinetobacter spp, therefore the Food and Drug Administration approved breakpoints for members of the family Enterobacteriaceae have been used.

A total of 30 (five strains were MDR and 25 strains were XDR) Acinetobacter strains were isolated from various clinical specimens (8 paracentesis fluid, 8 blood, 7 tracheal aspirates, 5 wound, 2 urine, 2 catheter, 1 sputum) of hospitalized patients in Turgut Ozal Medical Center in 2008 year. All of the MDR and XDR strains were susceptible to tigecyline by broth microdilution method. Against Acinetobacter spp, an MIC range between 0.03 and 0.5 μg/ml was observed by broth microdilution and MIC50 and MIC90 values were determined as 0.12 μg/ml and 0.25 μg/ml, respectively. Twenty five strains (83%) were found susceptible to tigecyline when the disk diffusion brekpoints were considered as ≥16mm susceptible and ≤12mm resistant. Against Acinetobacter spp, an MIC range between 1 and 8 μg/ml was observed by E test. MICs of tigecycline determined by E test were 8 to 64 times higher and 30% (9/30) of the isolates were resistant to tigecycline by E test (MIC breakpoint 2 μg/ml ). Broth microdilution method must to use in the resistant Acinetobacter spp, by E test and disk diffusion method.

Key Words: Acinetobacter spp; Multi-Drug-Resistance; Tigecycline; E Test; Broth Microdilution.

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