This study compared colony counts of mixed bacterial cultures on chromogenic spread plates using manual and Color QCount (Spiral Biotech, Inc., Norwood, MA) PRACTICAL APPLICATIONSA variety of microbiology applications require users to count bacterial colonies on agar plates. Colonies are counted to 1) assess levels of contamination in the environment, water, food and dairy products; 2) conduct preservative and efficacy studies; and 3) determine the quality of pharmaceutical and medical products with microbial limits testing. There are several sources of variability in plating including inoculating errors, sampling errors, incubation errors, and counting errors. Errors in counting may worsen with user fatigue.