Quantidisc and Yea Method Comparison: Recovery and Enumeration of Mesophilic Heterotrophic Bacteria in Potable Water

Historically, heterotrophic plate counts are enumerated using a pour plate method, whereby plates are read manually. This analysis is important to evaluate the maintenance of water disinfection in a reticulation system. Advances in media and technology have made it possible to do this evaluation using defined substrate media and enumeration is performed by means of instrumentation using software specifically developed for this purpose. A comparative study was made of the recovery and enumeration of mesophilic, aerobic bacteria in potable water using the IDEXX Quanti Disc ® YEA method and pour plate method. The IDEXX Quanti Disc ® YEA method recovered significantly more bacteria than the pour plate method. The IDEXX Quanti Disc ® YEA method eliminates media preparation, sterilization and dispensing, making it faster, more accurate and having less Quality Assurance steps. The instrumentation eliminates subjectivity in reading results and calculations and data transfer to the database can be interfaced. This method is only suitable for samples where the plate count is expected to be low, such as in drinking water. The heterotrophic plate count done on IDEXX Quanti Disc ® YEA does not need to be done in duplicate. The recovery is possibly higher because the nutrient value of the media is not compromised by re-heating, so more stressed organisms are able to grow. Dispersion of the sample is possibly improved.