ABSTRACT
The most probable number (MPN) technique is a quantitative method of analysis that allows determining the MPN of the target microorganisms in a sample by inoculating aliquots of that sample into a series of tubes containing a liquid culture medium appropriate to its growth. The multiple dilution tests is the most versatile format of the MPN technique, because it allows coverage of a wide range of microbial concentrations in the sample, by varying the inoculated dilutions. The selection of the dilutions will depend on the estimated contamination level of the sample, so as to obtain positive tubes for the smaller dilutions and negative tubes for the greater dilutions. The single dilution test is more used for the examination of samples with a low level of contamination, for which there is no reason to inoculate dilutions. The combination of positive and negative tubes in the MPN technique allows estimation of the density of the target microorganisms in the sample.
