[1]: 149 [2] The antibiotic to be tested is diluted with water to produce a series of concentrations.
An appropriate volume is then combined with melted agar to produce plates in which the final antibiotic concentrations represent a 2-fold dilution series.
Necessary controls include a control plate that does not receive any antibiotics and bacterial spread plates demonstrating that the bacteria included are in the correct concentration range.
[1]: 374 After incubation, the plates are examined to determine if bacterial growth has occurred in the inoculated spots.
[4] Agar dilution is considered to be the gold standard of susceptibility testing, or the most accurate way to measure the resistance of bacteria to antibiotics.