Agar dilution susceptibililty testing is regarded as the golden standard for all other
susceptibilily testing methods.
It is of course extremely important to be able to prepare the agar plates in such a way that the
obtained antimicrobial concentration in the plates are exactly or very close to the desired
concentrations
When preparing antimicrobial solutions and agar plates for agar dilution susceptibility
testing, we therefore strongly recommend following the international guidelines given by the
NCCLS (NCCLS document M7-A5 "Methods for dilution antimicrobial susceptibility tests
for bacteria that grow aerobically").
Instructions on how to prepare the antimicrobial solution are outlined in table 5 (NCCLS
document M100-S12) and further explained in appendices 1 and 2. The dilution procedure
might at first seem a little complicated, but this method ensures that there is minimal risk of
making out-of-scale-dilutions for the smallest concentrations in the test range.