Comparison of two methods for detection of Listeria monocytogenes in foods

Plate counting and MPN counting methods were used to detect Listeria monocytogenes in foods under different conditions of contamination for screening an accurate one, and the quantity of LM in the refrigenerated and frozen foods at different storage times was explored. The LM content of milk, salad and saltwater ducks with different degrees of artificial contamination were detected by Plate counting and MPN counting methods respectively. The LM content of milk, salad and saltwater ducks stored in cold storage(2~8℃) and frozen(-20℃) were tested by MPN counting method.The results showed that the accuracy of Plate counting method was higher than MPN counting method when the concentration of bacteria was low (LM:E.coli and SA is 10:1) and the detection limit of LM was high (≥ 100 CFU/g (mL)) while it was lower than MPN counting method in the condition of the high initial concentration of bacteria(LM:E.coli and SA is 1:10) and the detection limit of LM(< 100 CFU/g(mL)).The number of LM in foods(milk,salad and saltwater ducks) increased with the increase of cold storage and frozen time, and the number of LM in the above storage time of milk, salad and saltwater ducks had statistic significance(p<0.05).