Acinetobacter baumannii İzolatlarında Kolistin Heterodirencinin Araştırılması

Heterodirenç, kolistin direncinin gelişimi için bir adım kabul edilmektedir. Son yıllarda, farklı ülkelerden karbapenem dirençli A.baumannii (KDAB) izolatlarında kolistine karşı heterodirenç ve direnç gelişimi bildirilmiştir. Bu çalışmada, ilimizde ikinci basamak bir hastanenin çeşitli birimlerinden izole edilen KDAB izolatlarının kolistine karşı heterodirenç profillerinin araştırılması amaçlanmıştır. Haziran 2016 ve Haziran 2017 tarihleri arasında ikinci basamak hastaneden toplanan ve Üniversite Hastanemizin Tıbbi Mikrobiyoloji Anabilim Dalı arşivinde saklanan, kolistine duyarlı 47 KDAB izolatı çalışmaya dahil edilmiştir. İzolatların tanımlanması ve antibiyogramları otomatize sistem (Phoenix, BectonDickinson, ABD) ile yapılmıştır. Stoklanan bakterilerin kolistin minimum inhibisyon konsantrasyonları sıvı mikrodilüsyon yöntemi ile doğrulanmıştır. Heterodirençli alt popülasyonların tespiti için 4 µg/ml kolistin içeren Mueller-Hinton agar (MHA) petri plakları hazırlanmıştır. Plaklara, 100 mikrolitre KDAB bakteri süspansiyonu (108 CFU/ml) ilave edilmiştir. 24 saat inkübasyonun ardından MHA ’da üreme gösteren koloniler, heterodirençli olarak tanımlanmış ve manüel olarak koloni sayımı yapılmıştır. Toplanan tüm izolatlar kolistine karşı duyarlı ve karbapenemlere karşı dirençli bulunmuştur. İzolatların % 34’ünde (16/47 izolat) kolistine karşı heterodirenç tespit edilmiştir. Bu suşlarda heterodirenç oranları 10-7 ile 10-4 arasında gözlemlenmiştir. Çalışmamızda izolatlarda önemli oranda (% 34) heterodirenç saptanmıştır. Ülkemizde, kolistin heterodirenci ile ilgili çalışmalar sınırlı sayıdadır. Bu çalışmamız ülkemizde KDAB izolatlarında kolistin heterodirencinin raporlandığı ilk araştırmalardan biridir. Bununla beraber, kolistin heterodirencinin gerçek oranını ve klinik önemini ortaya koymak için yeni ve daha geniş çalışmalar gereklidir.

Investigation of Colistin Heteroresistance Among Acinetobacter baumannii Isolates

Colistin heteroresistance is a step for the development of full colistin resistance. Recently, heteroresistance and resistance to colistin have been reported for carbapenem-resistant Acinetobacter baumannii (CRAB) isolates in different countries. In this study, we aimed to investigate colistin heteroresistance profiles of CRAB strains isolated from various units of a secondary care hospital in our city. Forty-seven colistin susceptible CRAB isolates stored in our University Hospital Medical Microbiology Department collection and previously collected from secondary care hospital between June 2016 and June 2017 were included in the study. Identification and antibiograms of the isolates were performed by the automated system (Phoenix, Becton-Dickinson, USA). Colistin MICs were confirmed by broth microdilution test for the stored bacteria. Mueller-Hinton agar (MHA) plates containing colistin at concentration of 4 µg/ml were prepared for detection of heteroresistant subpopulations. The plates were inoculated with 100 microliters amount from CRAB bacterial suspensions (108 CFU/ml). Colonies which were able to grow on MHA plates after 48 hours incubation were defined as heteroresistant and counted manually. All isolates were susceptible to colistin and resistant to carbapenems. Among 47 CRAB isolates, 16 isolates (34 %) were found heteroresistant to colistin. The rates of heteroresistance for these isolates were between 10-7 and 10-4. In our study, we detected a significant rate of heteroresistance (34 %) to colistin. In our country, there are limited numbers of studies about heteroresistance to colistin. This study may be one of the first researches reporting the existence of colistin heteroresistance among CRAB isolates in our country. New and larger studies are necessary to evaluate the real rate and clinical importance of colistin heteroresistance.

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