Evaluation of three applications of a semi-automated most-probable-number method for the assessment of microbiological parameters in dairy products

Several rapid and automated microbiological methods have been introduced by food control laboratories because they allow microbiological quality (e.g. contamination with spoilage microorganisms and/or pathogens) of products to be checked or hygiene monitoring undertaken during production. This study evaluated three applications of the TEMPO® system; an automated method based on the most-probable-number technique, performed in parallel with the relevant ISO standard method for comparison. Escherichia coli certified reference material and soft cheese samples contaminated artificially with E. coli were used throughout the study. Performance characteristics including precision, bias and limit of detection of E. coli (EC), coliforms (TC) and viable aerobic mesophilic microflora (TVC) were determined with particular attention given to low-level contamination, which typically occur in manufacturing and retail as well as storage and consumption at home. TEMPO® EC was more precise than TEMPO® TC whilst TEMPO® TVC showed the most variation. Moreover, higher numbers of E. coli were obtained with TEMPO® EC than TEMPO® TC. Reliability of the system depended on the specificity of detection of the targeted group of microorganisms as well on the method. Although, methods like TEMPO® offer convenience, they often lack the necessary clarity in terms of operational details, measurement principles and data processing necessary for reliable routine use. Installation of an ‘expert modus’ to facilitate access to original data would significantly increase commercial confidence in the application and use of these systems.