Determination of Colistin Resistance by Simple Disk Diffusion Test Using Modified Mueller-Hinton Agar
Jean Damascene Uwizeyimana, Daewon Kim, Hyun-Sook Lee, Jung‐Hyun Byun, Dongeun Yong
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: complex (N=33). Disk diffusion test results were interpreted based on minimum inhibitory concentrations determined by broth microdilution. RESULTS: <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.