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

Abstract

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.

Keywords

• Acinetobacter spp; Multi-Drug-Resistance; Tigecycline; E Test; Broth Microdilution.

Çoğul Direnç veya Ekstrem İlaç Direnci Olan 30 Acinetobacter Suşunda in Vitro Tigesiklin Duyarlılığının Disk Difüzyon, E-test ve Buyyon Mikrodilüsyon Yöntemleri ile Değerlendirilmesi

Öz

Acinetobacter türleri sıklıkla nozokomiyal enfeksiyonlara neden olurlar ve çoğu antimikrobiyal ajana dirençlidirler. Bu çalışmada çoğul dirençli (MDR) veya extreme-reziztans (XDR) olarak tanımlanmış Acinetobacter izolatlarında tigesiklin duyarlılığı üç ayrı yöntem ile değerlendirilmiştir. Üçten fazla ilaca (imipenem, meropenem, seftazidime, sefepime, aztreonam, piperasilin-tazobaktam, siprofloksasin, tetrasiklin, ampisilin-sulbaktam, trimetoprim-sülfametoksazol, amikasin, gentamisin ve tobramisin) dirençli olanlar MDR ve tigesiklin ile kolistin dışındaki tüm antibiyotiklere dirençli olanlar XDR olarak alınmıştır. Turgut Özal Tıp Merkezinde 2008 yılında yatan hastalara ait 8 parasentez sıvısı, 8 kan, 7 trakeal aspirat, 5 yara, 2 idrar, 2 katater ve 1 balgamdan izole edilen 30 (beşi MDR ve 25'i XDR) Acinetobacter suşu çalışmaya alınmıştır. Acinetobacter izolatları konvansiyonel yöntemler ile tanımlanmış, antibiyotik duyarlılık testleri Clinical and Laboratory Standards Institute (CLSI) standartlarına göre yapılmıştır. İzolatların tümü karbapenem dirençli olarak değerlendirilmiştir. Tigesiklin duyarlılığı için disk difüzyon, E test (AB BIODISK, Solna, Sweden) ve buyyon mikrodilüsyon yöntemleri kullanılmıştır. Acinetobacter suşlarında tigesiklin için onaylanmış MİK sınır değerleri bulunmadığından, buyyon mikrodilüsyon ve E test sonuçları Enterobacteriaceae ailesi için United States Food and Drug Administration'ın (U.S. FDA) onayladığı tigesiklin MİK sınır değerine (≤ 2 µg/ml duyarlı) göre yorumlanmıştır. MDR ve XDR izolatlarının tümü buyyon mikrodilüsyon testi ile tigesikline duyarlı bulunmuştur. Buyyon mikrodilüsyon çalışılan 30 suşun MİK değerleri 0.03-0.5 μg/ml değerleri arasında olup, MİK50 değeri 0.12 μg/ml, MİK90 değeri 0.25 μg/ml olarak saptanmıştır. Tigesiklin disk difüzyon testinde ≥16mm duyarlı ve ≤12mm dirençli inhibisyon zon çapları kullanılarak 25 suş (% 83) duyarlı bulunmuştur. E test çalışılan 30 suşun MİK değerleri 1-8 μg/ml arasında saptanmıştır. E test ile elde edilen MİK değerleri gerçek MİK değerlerinden 8-64 kat fazla olup, çalışılan Acinetobacter suşlarının %30 (9/30)'u hatalı olarak dirençli bulunmuştur (2 μg/ml MİK kırılma noktasına göre). Sonuç olarak disk difüzyon yöntemi ve E test ile tigesikline dirençli bulunan Acinetobacter suşları için direnci doğrulamada buyyon mikrodilüsyon yöntemi çalışılmalıdır. Anahtar kelimeler: Acinetobacter spp; Çoğul İlaç Direnci; Tigesiklin; E Test; Buyyon Mikrodilüsyon.

Anahtar Kelimeler

• Acinetobacter spp; Çoğul İlaç Direnci; Tigesiklin; E Test; Buyyon Mikrodilüsyon.

Kaynakça

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