title: Agar and broth dilution methods to determine the minimal inhibitory concentration (MIC) of antimicrobial substances.
abstract: The aim of broth and agar dilution methods is to determine the lowest concentration of the assayed antimicrobial agent (minimal inhibitory concentration, MIC) that, under defined test conditions, inhibits the visible growth of the bacterium being investigated. MIC values are used to determine susceptibilities of bacteria to drugs and also to evaluate the activity of new antimicrobial agents. Agar dilution involves the incorporation of different concentrations of the antimicrobial substance into a nutrient agar medium followed by the application of a standardized number of cells to the surface of the agar plate. For broth dilution, often determined in 96-well microtiter plate format, bacteria are inoculated into a liquid growth medium in the presence of different concentrations of an antimicrobial agent. Growth is assessed after incubation for a defined period of time (16-20 h) and the MIC value is read. This protocol applies only to aerobic bacteria and can be completed in 3 d.
authors.affiliation: Centre for Microbial Diseases and Immunity Research, University of British Columbia, 2259 Lower Mall Research Station, Vancouver, British Columbia, V6T 1Z4, Canada.
authors.forename: Irith
authors.initials: I
authors.lastname: Wiegand
authors.forename: Kai
authors.initials: K
authors.lastname: Hilpert
authors.forename: Robert E W
authors.initials: RE
authors.lastname: Hancock
mesh_terms: D000362:Agar; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001420:Bacteria, Aerobic / Q000187:drug effects*; D003470:Culture Media; D024881:Drug Resistance, Bacterial; D008826:Microbial Sensitivity Tests / Q000379:methods*; D013997:Time Factors
chemical_list: D000900:Anti-Bacterial Agents; D003470:Culture Media; D000362:Agar