Colistin Susceptibility Testing Methods for Carbapenem Resistant Acinetobacter baumannii, A Comparative Study

Document Type : New and original researches in the field of Microbiology.


Medical Microbiology and Immunology, Faculty of Medicine, Alexandria University


Background: Acinetobacter baumanii is an emerging nosocomial pathogen that is associated with several infections that are extremely difficult to treat. Extensive and pan-drug resistance to multiple antibiotic classes is rising leading to limited treatment options and making colistin a last resort. Practical and accurate susceptibility testing methods are a mandatory demand for rapid and reliable sensitivity reporting of colistin. Objective: The aim was to test colistin sensitivity of carbapenem-resistant Acinetobacter baumanii, using different commonly used testing methods in the routine microbiology laboratory as disc diffusion, broth microdilution, E-test and Vitek-2 system. Results: This research showed that disc diffusion and E-test failed to meet the CLSI criteria with high very major errors (100% and 33%). Comparative evaluation between the three studied antibiotic susceptibility methods to colistin against broth microdilution as a reference method, showed 100% categorical agreement with Vitek-2. Conclusion: We concluded that besides the reference broth microdilution method, Vitek-2 is an automated alternative reliable option to test the bacterial susceptibility to colistin in the laboratory.


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