The aim of this study was to compare the MPN-PCR (Most Probable Number- Polymerase Chain Reaction) and MPN-Culture methods in enumerating of Listeria monocytogenes in milk. In order to compare the accuracy of these methods, 103 cell/ml Listeria monocytogenes and different background bacteria which may be present in raw milk, were inoculated in sterilized milk. After preparing serial dilutions, three replicates per dilution were inoculated in tubes containing listeria enrichment broth. After 48 hours of incubation, for MPN-Culture three inoculated replicates were subcultured on Oxford agar and suspected colonies were confirmed by performing by biochemical tests.
For MPN-PCR assay, the DNA extraction was performed from the three inoculated replicates which were already used for MPN-Culture and PCR assay was performed using primers specific for Listeria monocytogenes.
The experiment was repeated three times and the average of enumerated bacteria was calculated by each method separately.
Statistical analysis using one sample Wilcoxon signed rank test showed that enumeration by MPN-PCR method was more accurate than enumeration by MPN-Culture method.
The result of this study showed that MPN-PCR method in comparision with MPN-Culture even in the presence of different background microorganisms is more rapid and reliable. It is concluded that MPN-PCR method facilitates the enumeration of Listeria monocytogenes without excessive work and could be considered as an alternative to MPN-Culture technique.