Evaluation of heterotrophic plate and chromogenic agar colony counting in water quality laboratories

The enumeration of bacteria using plate-based counts is a core technique used by food and water microbiology testing laboratories. However, manual counting of bacterial colonies is both time and labour intensive, can vary between operators and also requires manual entry of results into laboratory information management systems, which can be a source of data entry error. An alternative is to use automated digital colony counters, but there is a lack of peer-reviewed validation data to allow incorporation into standards. We compared the performance of digital counting technology (ProtoCOL3) against manual counting using criteria defined in internationally recognized standard methods. Digital colony counting provided a robust, standardized system suitable for adoption in a commercial testing environment. The digital technology has several advantages: • Improved measurement of uncertainty by using a standard and consistent counting methodology with less operator error. • Efficiency for labour and time (reduced cost). • Elimination of manual entry of data onto LIMS. • Faster result reporting to customers.