Objective: Klebsiella pneumoniae can be found colonized on human skin, gastrointestinal flora and nasopharynx. We aimed to examine the increase level of minimal inhibitory concentration values of colistin is alternative treatment in carbapenem resistant Klebsiella pneumoniae and to compare the results of automated system with gold standard fluid microdilution method of colistin sensitivity.

Method: Sixty-six carbapenem resistant Klebsiella pneumoniae strains isolated from clinical samples between January 2015-July 2017 were included in the study. Carbapenem susceptibilities of strains studied with automated system were also tested by disk diffusion method. To measure colistin sensitivities, liquid microdilution test was studied using colistin sulfate active substance in accordance with EUCAST recommendations. The MIC range for colistin was studied with values between 0.125-64 ?g/ml. Chi-square test was used to analyze the data.

Results: A total of 24 (36.4%) isolates, 6 (37.5%) in 2015, 8 (35.8%) in 2016 and 10 (41.7%) in 2017, were found to be resistant to colistin. No statistically significant difference was found in the MIC values of colistin over the years (p>0.05). There was discrepancy between the results found by two different methods. Very major errors were detected in two isolates and major errors were detected in two isolates.

Conclusion: It is worrisome that carbapenem resistant Klebsiella pneumoniae isolates were detected in about one-third of colistin resistance. Also, it?s important to determine the resistance rates with gold standard fluid microdilution method. This reduces the treatment options alone or in combination, suggesting that these isolates will become more difficult to treat in future and new treatment strategies should be studied.