Determination of colistin resistance by simple disk diffusion test using modified Mueller-Hinton agar

Jean Damascene Uwizeyimana, Daewon Kim, Hyunsook Lee, Jung Hyun Byun, Dongeun Yong

Research output: Contribution to journalArticle

Abstract

Background: Colistin has become a last-resort antibiotic for the management of multidrug-resistant gram-negative bacteria. The disk diffusion test is cheap and easy to perform but may be unreliable for colistin susceptibility testing due to poor diffusion of the large colistin molecule. An improved agar diffusion test would increase the reliability of colistin susceptibility testing. This study aimed to modify Muller-Hinton agar (MHA) to improve colistin diffusion in agar. Methods: MHA was modified by reducing the agar concentration from 100% to 30% and supplementing with protamine. We tested 60 gram-negative clinical isolates of Pseudomonas aeruginosa (N = 27) and Acinetobacter calcoaceticus-baumannii complex (N = 33). Disk diffusion test results were interpreted based on minimum inhibitory concentrations determined by broth microdilution. Results: The modified MHA yielded the best performance metrics, including 94.7% sensitivity, 100% specificity, and an area under the curve of 0.995 (95% confidence interval, 0.982-1.000), P < 0.001, at a cut-off point of 13 mm. Conclusions: A reduction of the agar concentration from 100% to 30% and the addition of protamine improved colistin diffusion in agar and allowed routine colistin susceptibility testing in a clinical microbiology laboratory, but should be handled with caution.

Original languageEnglish
Pages (from-to)306-312
Number of pages7
JournalAnnals of laboratory medicine
Volume40
Issue number4
DOIs
Publication statusPublished - 2020

All Science Journal Classification (ASJC) codes

  • Clinical Biochemistry
  • Biochemistry, medical

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