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PCR quantifies dead cells beside live cells and this makes the judgment of microbial quality of food samples complicated. The objective of this study was comparing the efficacy of ethidium monoazide-qPCR and propidium monoazide-qPCR in quantifying live pathogen cells (E.coli, Staphylococcus aureus, Enterococcus fecalis and Listeria monocyogenes) by real time PCR, in low-fat and high-fat milk, lactic cheese (low-fat) and processed cheese (high-fat). Different proportions of live and heat killed pathogen cells were inoculated into food samples. After separating bacterial pellets, EMA and PMA treatments qPCR was conducted. One-way ANOVA followed by Turkey’s Multiple Comparison tests were applied to analyze the data. In low-fat milk, EMA treatment resulted in 18, 20, 23 and 30% decrease in cell count of E.coli, S.aureus, E. fecalis and L. monocyogenes, respectively, compared to conventional culturing. Also, following treatment by PMA, 6, 3, 8 and 12% decrease in cell count was obtained for E.coli, S.aureus, E. fecalis and L. monocyogenes, respectively, compared to conventional culturing. In high-fat samples as processed cheese, a reduction of 20, 27, 30 and 25%  in EMA treatment and 9, 6, 5 and 10% in PMA treatment was observed in cell count of E.coli, S.aureus, E. fecalis and L. monocyogenes , respectively. The inhibitory potential of EMA and PMA against signal emission was variable in different bacterial species and the fat content of the samples exerted no significant effect  (p>0.05) on PMA and EMA functionality.

Keywords: ethidium monoazide food model system pathogen PCR propidium monoazide

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