A Critical Evaluation of Automatic Bacterial Colony Counters

Abstract

Four automatic colony counters (ACC), 3M Model 620 and Artek Models 480, 870 and 880, were evaluated for their precision and accuracy in counting bacterial colonies in pour-plates prepared using raw and pasteurized milk samples. The automatic colony counters were precise, labor saving devices. but not one of the ACC units approached our acceptability criterion that 90% of the ACC counts fall within ± 10% of the corresponding manual count. Some parameters of experimental design and instrument calibration which may significantly influence the response and performance of the automatic counters are discussed.