Evaluation of Diagnostics Colistin MIC-Strip Test for Colistin Susceptibility Testing

Due to the limited number of antimicrobials to be used in the treatment of infections caused by Gram-negative microorganisms with multi-drug resistance recently, old antibiotics such as colistin have started to be preferred frequently. However, some problems are encountered in antibiotic susceptibility tests (disk diffusion, gradient test, automated systems) which are frequently used in the routine laboratory due to the cationic nature of colistin. For this reason, only the broth microdilution test is recommended by European Committee on Antimicrobial Susceptibility Testing (EUCAST) and Clinical and Laboratory Standards Institute (CLSI) for the detection of colistin susceptibility. Since broth microdilution tests are time consuming and inconvenient, tests that can provide fast and reliable colistin susceptibility result is needed in routine laboratories. In this study, it was aimed to evaluate the performance of the commercially produced Diagnostics MIC-COL test (Diagnostics I.n.c, Galanta, Slovakia) for the detection of colistin susceptibility in Klebsiella pneumoniae and Acinetobacter baumannii strains. The strains of K.pneumoniae (n = 22) and A.baumannii (n = 28) isolated from various clinical specimens between 2016 and 2019 in our routine laboratory were included in the study. Colistin minimum inhibitory concentrations (MIC) of the strains were studied with both the reference broth microdilution method and the commercially produced Diagnostics Colistin MIC-COL test. The essential agreement, categorical agreement, major error, and very major error rates of the test were calculated by comparing the obtained results. The essential agreement of the Diagnostics Colistin MIC-Strip test was determined as 84 %, categorical agreement as 98 %, and major error rate as 3.8 %, while no very major error was detected. İt is very important to guide antimicrobial treatment with rapid and reliable detection of colistin susceptibility. The commercial test used in our study is easy to use and not time-consuming. Also, due to its strip from, each isolate can be studied separately. Because of the major error rate being above the expected values, it will be useful to re-evaluate these rates with further studies to be conducted with a larger number of strains with different resistance levels.