Evaluation of a dispensing instrument (Dynatech MIC-2000) for preparing microtiter antibiotic plates and testing their potency during storage.

The MIC-2000 96-channel dispenser was evaluated for accuracy and repeatability of dispensing 50-mul volumes of water. It was found to perform within the manufacturer's specifications for accuracy of +/-5%, but not within the limits for repeatability of +/-1%. Overall, instrument performance was found to be satisfactory for the antimicrobial susceptibility testing technique which has been implemented in this laboratory. A method is suggested for simple evaluation of the volumes dispensed. A variety of antibiotics may be stored in Trypticase soy broth in Microtiter plates without loss of potency for periods of at least 2 weeks at -20 degrees C and 4 months at -70 degrees C.