Comparison of an Automated Most Probable Number (MPN) Technique to a Manual Method for the Enumeration of Total Aerobic Counts in Food Contact Surface Samples

Introduction:  The enumeration of total aerobic counts in food contact surface samples is critical when assessing the sanitary state and bacterial load in the food production environment. Traditional microbial enumeration techniques consist of time-consuming and labor-intensive steps including serial dilution preparation, plating and colony counting. The TEMPO^®TVC method is an automated system for the enumeration of total aerobic mesophilic flora that eliminates these objectionable steps. The method uses an enumeration card containing 48 wells across three different dilutions for the automatic determination of MPN.

Purpose:  To compare an automated MPN based system to a manual method for the enumeration of total aerobic counts in food contact surface samples from a commercial chicken production facility in the USA.

Methods:  Fifty food contact surface swab samples were collected randomly from a poultry production facility and were processed to enumerate the total aerobic counts using the TEMPO^® TVC system and Petrifilm™ Aerobic Count Plates. The log values of counts (CFU/ml) enumerated by each method were analyzed statistically for the calculation of overall bias and correlation coefficient between the methods.

Results:  A 95% confidence interval of the bias was calculated for the log values (CFU/ml) of total aerobic counts enumerated by each method. The calculated confidence interval contained the integer 0; therefore, it can be concluded that no significant bias was observed between the methods evaluated in this study. The correlation coefficient between the automated MPN and the manual method was found to be high (0.953). 

Significance:  The automated MPN system provides an accurate and easy-to-use approach for the enumeration of total aerobic counts in food contact surface samples. The automated system eliminates the need for media preparation, serial dilutions, manual counting and visual interpretation of results. This, in turn, provides rapid results with the additional advantages of significant economic labor savings, increased efficiency and better traceability.