Determining colistin resistance in acinetobacter baumannii species in eight-compartment colistin agar medium

Öz

Aim: Acinetobacter baumannii strains are opportunistic nosocomial pathogens that are frequently multi-drug resistant and have a high mortality rate. In this study, we aimed at evaluating the colistin resistance pattern in Acinetobacter clinical isolates through comparison using tube dilution and agar dilution methods, as well as the performance of a single petri dish with eight compartments that is not in routine use. Material and Methods: In the study, A. baumannii, which was isolated from 104 patients hospitalized in Samsun Training and Research Hospital between 2018 and 2019 in various clinics and identified in the automatic bacteria identification device (VITEK 2, Biomerioux, France). The colistin resistance of the strains was determined by tube dilution and agar dilution methods. Agar dilution test was performed in a single petri dish with eight compartments and Mueller Hinton Agar Medium supplemented with colistin at a concentration of 0.125-16 µg/ml. The results were interpreted according to The European Committee on Antimicrobial Susceptibility Testing (EUCAST) data, and a Minimal Inhibitory Concentration (MIC) value of 2 µg/ml and less was accepted as a colistin sensitive strain. Results: Of the 104 strains included in the study, 68 (65.4%) were sensitive to colistin in the automated system, 66 (63.5%) in the liquid tube dilution test, and 64 (61.5%) in the agar dilution test. While 38 (36.5%) strains were resistant to colistin in the tube dilution test, 40 (38.5%) strains were found to be resistant to colistin in agar dilution test. 2µg/ml and less was accepted as sensitive to colistin in the resistance test. However, due to the chosen sample group, no colistin sensitivity was observed at 0.125 and 0.250 µg/ml concentrations in the resistance test. While the most seen MIC value in the tube dilution method was 1 µg/ml, the most seen MIC value in agar dilution was 2 µg/ml. Conclusion: In the study, no significant difference was found between agar and tube dilution methods. The laboratory provided a cost advantage to the as a result of the resistance study performed on a single colistin agar medium with eight compartments.

Anahtar Kelimeler

• Colistin resistance
• tube dilution test
• agar dilution

Sekiz bölmeli kolistinli agar besiyerinde acinetobacter baumannii türlerinde kolistin direncinin saptanması

Öz

Amaç: Acinetobacter baumannii suşları sıklıkla çoklu ilaç direnci gösteren ve mortalite oranı yüksek opurtunistik nasokomiyal patojenlerdir. Bu çalışmada, Acinetobacter klinik izolatlarında kolistin direnç paterninin tüp dilüsyon ve agar dilüsyon yöntemleriyle kıyaslamalı olarak değerlendirilmesinin yanı sıra rutin kullanımda olmayan sekiz bölmeli kolistinli agar besiyerinin performansının değerlendirilmesi amaçlanmıştır. Gereç ve Yöntemler: Çalışmada, Samsun Eğitim ve Araştırma Hastanesi’de 2018-2019 yılları arasında çeşitli kliniklerinde yatmakta olan 104 hastadan izole edilen ve tam otomatik bakteri identifikasyon cihazında (VITEK 2, Biomerioux, France) tanımlaması yapılmış A.baumannii suşlarının kolistin direnci tüp makro dilüsyon ve agar dilüsyon yöntemleriyle saptandı. Agar dilüsyon testi, sekiz sabit bölmeli tek bir petri kutusunda ve 0,125-16 µg/ml konsantrasyonda kolistin ilaveli Mueller Hinton agar besiyerinde yapıldı. The European Committee on Antimicrobial Susceptibility Testing (EUCAST) verilerine göre yorumlama yapılarak, 2 µg/ml ve altı minimal inhibitor konsantrasyon (MİK) değeri kolistine duyarlı suş olarak kabul edildi. Bulgular: Çalışmaya dâhil edilen 104 suşun 68’i (%65,4) otomatize sistemde, 66’sı (%63,5) sıvı tüp dilüsyon testinde, 64’ü (%61,5) agar dilüsyon testinde kolistine duyarlı olarak saptandı. Tüp dilüsyon testinde 38 (%36,5) suş kolistine dirençli iken, agar dilüsyon testinde ise 40 (%38,5) suş kolistine dirençli olarak tespit edildi. Direnç testinde 2µg/ml ve altı kolistine duyarlı kabul edildi. Ancak seçilen örneklem grubu nedeniyle direnç testinde 0,125 ve 0,250 µg/ml konsantrasyonlarda kolistin duyarlılığı görülmedi. Tüp dilüsyon yönteminde en fazla görülen MİK değeri 1 µg/ml iken agar dilüsyonunda en fazla görülen MİK değeri 2 µg/ml idi. Sonuç: Sunduğumuz çalışmada agar ve tüp dilüsyon yöntemleri arasında anlamlı bir fark bulunamamıştır. Sekiz bölmeli tek bir kolistinli agar besiyerinde yapılan direnç çalışması sonucu laboratuvar maliyet avantajı sağlamaktadır.

Anahtar Kelimeler

• Sekiz bölmeli agar
• Kolistin direnci
• Acinetobacter spp.

Kaynakça

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