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2014, Cilt 44, Sayı 4, Sayfa(lar) 144-148
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In-Vitro Activity of Vancomycin Against Colistin Resistant Acinetobacter baumannii Strains
Deniz GAZEL1, Özlem ZANAPALIOĞLU GAZEL2, Alper AKÇALI3, Müşerref TATMAN OTKUN3
1Çanakkale Devlet Hastanesi, Mikrobiyoloji Laboratuvarı, Çanakkale
2Çanakkale Onsekiz Mart Üniversitesi Tıp Fakültesi, Enfeksiyon Hastalıkları ve Klinik Mikrobiyoloji Anabilim Dalı, Çanakkale
3Çanakkale Onsekiz Mart Üniversitesi Tıp Fakültesi, Tıbbi Mikrobiyoloji Anabilim Dalı, Çanakkale
Keywords: Acinetobacter baumannii, colistin, vancomycin

Aim: Acinetobacter baumannii strains are naturally resistant to vancomycin. We aimed to investigate the in-vitro activity of vancomycin against colistin resistant A. baumannii strains.

Material and Methods: A. baumanii ATCC19606 which is colistin susceptible and two A. baumannii isolates, one colistin susceptible and one colistin resistant, from the same patient were included in the study. Colistin MIC values of the colistin susceptible blood isolate and ATCC strain were determined by E-test (Oxoid, United Kingdom). Then, these strains were transformed to colistin resistant forms using Li's method by colistin exposure at increasing concentrations. New MIC values were determined for vancomycin and colistin. MICs were also determined for the colistin resistant strain isolated from the cerebrospinal fluid (CSF) sample of the same patient.

Results: While MIC values for both ATCC strain and colistin susceptible blood isolate were 0.4 μ/ml, after transformation to resistant forms, colistin MICs of the strains raised to 48 and 32 μg/ml, respectively. These two strains were initially resistant to vancomycin (>256 μg/ml), however, following transformation, MICs for vancomycin decreased to 0.5 and 3 μg/ml, respectively. For the CSF isolate, vancomycin and colistin MICs were determined as 128 and 12 μg/ml, respectively.

Conclusion: Following colistin exposure at increasing concentrations, colistin MIC values increased while vancomycin MIC values decreased. This indicated a possible negative correlation between vancomycin and colistin MIC values. For strains exhibiting colistin MIC values above 32 μg/ml, vancomycin may have inhibitory activity. In this study, it was shown that vancomycin MICs decreased for the strains that had gained colistin resistance. In-vitro synergy testing must be performed to show that vancomycin-colistin combinations may prevent selection of colistin resistant strains.


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