An agar dilution method is used for routine testing. The antimicrobial is added to agar in various concentrations depending upon levels attainable in serum, urine, or both. A standardized suspension of the organism is applied to the agar plates which are incubated for a minimum of 16 to 18 hours at 35 degrees C. Complete inhibition of all but 1 colony or a very fine residual haze represents the end point.(Clinical and Laboratory Standards Institute 2015 Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria That Grow Aerobically; Approved Standard. Tenth Edition [M07-A10] CLSI, Wayne, PA)
Bacterial isolates are retained for 30 days.