[The Use of Resapolymyxin NP Test in Determining the Sensitivity of Colistin in Escherichia coli, and Klebsiella pneumoniae Isolates].

Colistin is used as the last choice of drug in multidrug resistant gram-negative bacilli infections; therefore, accurate detection of colistin susceptibility has gained critical importance. Unfortunately, many of the widely used and practical methods in the clinical laboratory have various limitations for the determination of colistin susceptibility. This situation has led researchers to search for new methods to determine colistin susceptibility. In this study, the performance of the ResaPolymyxin NP test, which was developed for the rapid detection of colistin susceptibility of Pseudomonas aeruginosa and Acinetobacter baumannii isolates, was evaluated for various Gram-negative bacteria for the determination of colistin susceptibility. For this purpose, the colistin MIC values of 105 Escherichia coli, and 196 Klebsiella pneumoniae isolates were determined by broth microdilution (BMD) using cation-adjusted Mueller-Hinton broth and then ResaPolymyxin NP test was applied for each isolate. While 242 (%80.4) of the isolates included in the study were found to be susceptible to colistin with BMD, 214 (71.1%) of the isolates were found as sensitive to colistin with the ResaPolymyxin NP test. The categorical agreement rate for the ResaPolymyxin NP test was 85.7% for E.coli isolates, and 92.3% for K.pneumoniae isolates. The major error rate was 14.7% for E.coli, 10.8% for K.pneumoniae, whereas the very major error rate was 1.8% for K.pneumoniae. For ResaPolymyxin NP test, sensitivity, specificity, positive and negative predictive values were %98,3; %88.0; %66.7; and %99.5. In contrast to the available data about the ResaPolymyxin NP test, both the categorical agreement rate with BMD, and the very major and major error rates varied according to the isolate type, and it was concluded that the test performed relatively better in E.coli and K.pneumoniae isolates. Since the data obtained in this study are quite different from the previously published data, more comprehensive and multicenter studies are needed to evaluate the test effectiveness in order to recommend the use of the ResaPolymyxin NP test in clinical microbiology laboratories.