Comparison of the Results of the Microdilution and Automated System in Determination of Colistin Resistance

Abstract

Aim: Colistin is one of theantibiotics with increasing usage in the treatment of multidrug-resistant Gram-negative bacteria. The Mueller-Hinton broth microdilution (BMD) method proposed by the European Committee on Antimicrobial Susceptibility Testing (EUCAST) is the gold standard for the determination of sensitivity. The aim of this study was to compare the sensitivity of the Vitek2 Compact automated device with BMD results. Material and Methods: Total of 126 Gram negative isolates participated in the study. Colistin sensitivity of the isolates was determined by Vitek2 Compact automated system and BMD method. Results: Sixteen of 126 isolates in the automated system were found to be colistin resistant (12.7%). Colistin resistance was found in 34 (126%) out of 126 isolates with BMD. These two methods, the categorical adjustment (KU) ratio for the automated system was found to be 84.12%, majör error (BH) was 1.09%, and very large error (MDI) was 55.88%. The minimum inhibitory concentration values (MIC50 and MIC90) of the isolates studied in the automated system were 0.5 μg / ml and16 μg / ml. The MIC50 and MIC90 values of the results obtained by BMD method were 0.5 μg / ml and 2 μg / ml. Conclusion: When the automated system results are examined, it is seen that the rate of resistant isolates is less. With these results it is seen that resistant isolates can be overlooked in automated system. In the sensitivity of colistin, it was seen that the automated system did not fully meet the expectations.

Keywords

• Antimicrobial susceptibility
• colistin
• broth microdilution

Kolistin Direncinin Saptanmasında Sıvı Mikrodilüsyon ve Otomatize Sistem Sonuçlarının Karşılaştırılması

Abstract

Amaç: Kolistin çok ilaca dirençli Gram negatif bakterilerin tedavisinde kullanımı artan antibiyotiklerden biridir. Duyarlılığının belirlenmesinde European Committee on Antimicrobial Susceptibility Testing (EUCAST) tarafından önerilen Mueller-Hinton buyyonda sıvı mikrodilüsyon (BMD) yöntemi altın standart olarak belirlenmiştir. Bu çalışmada Vitek2 Compakt otomatize cihazının belirlediği duyarlılık sonucuyla BMD yönteminin sonuçlarının karşılaştırılması amaçlanmıştır. Gereç ve Yöntemler: Çalışmaya 126 Gram negatif izolat dahil edilmiştir. Bu izolatların kolistin duyarlılığı Vitek2 Compakt otomatize sistemiyle belirlenmiş olup tüm örneklerin kolistin duyarlılığı BMD yöntemi ile de çalışılmıştır. Bulgular Otomatize sistemde 126 izolatın 16 tanesi kolistin dirençli olarak bulunmuştur (%12,7). BMD yönteminde 126 izolatın 34 tanesi kolistin dirençli olarak bulunmuştur (%27). İki yöntem karşılaştırıldığında otomatize sistem için kategorik uyum (KU) oranı %84,12, büyük hata (BH) oranı %1,09, çok büyük hata (ÇBH) oranı da %55,88 olarak saptanmıştır. Otomatize sistem ile incelenen izolatların minimum inhibitör konsantrasyon değerleri (MİK50 ve MİK90) sırasıyla 0,5 μg/ml ve 16 μg/ml olup BMD yöntemi ile elde edilen sonuçların MİK50 ve MİK90 değerleri sırasıyla 0,5 μg/ml ve 2 μg/ml olarak bulunmuştur. Sonuç: Otomatize sistem sonuçlarına bakıldığında dirençli izolat sayısının daha az olduğu görülmektedir. Bu sonuçlar ile otomatize sistemde dirençli olan izolatların gözden kaçabileceği görülmektedir. Kolistin duyarlılığında EUCAST’ın önerdiği BMD yönteminin kullanılmasının gerekliliği ve otomatize sistemlerin beklentileri tam olarak karşılamadığı bu çalışma ile vurgulanmıştır.

Keywords

• kolistin
• Antimikrobiyal duyarlılık
• sıvı mikrodilüsyon

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