An economical and time saving alternative to the most-probable-number method for the enumeration of microorganisms

Abstract

A modification of the most-probable-number (MPN) method for the determination of total viable microbial cells was investigated. This alternative method (AMPN) applies MPN statistics to microorganisms growing on solid instead of liquid medium which is used in the conventional method. To verify the validity of the proposed method, numbers obtained with the AMPN were compared to counts from drop-plate (DP) and spread-plate (SP) methods. Correlation and regression analysis showed a positive correlation between the AMPN and the DP and SP methods. Also, the Student t test applied for paired samples showed no difference between the mean values of replicates and the methods tested at the 5% level of significance. The advantages and disadvantages of the alternative method under defined conditions are discussed. Since the results obtained with the AMPN were equivalent to results from DP and SP methods we adopted this system for its reliability and cost-effectiveness.