TABLE 1.

RTi-PCR-based detection of L. monocytogenes with three filtration strategies and with and without Chelex-100-based DNA purification^a

Approx no. of CFU/g	Signal ratio with indicated treatment
	Chelex-100			No Chelex-100
	F1	F2	F3	F1	F2	F3
106	+	+	+	+	+	+
105	+	+	+	3/6	+	+
104	+	+	+	4/6	+	+
103	+	+	+	1/6	3/6	3/6
102	6/8	4/8	5/8	0/8	1/8	0/8
101	0/8	0/8	0/8	0/8	0/8	0/8

^aF1, F2, and F3 correspond to alternative pre-PCR filtration steps. F1 indicates no filtration, F2 indicates filtration with 22- to 25-μm-pore-size filters, and F3 indicates filtration with an 11-μm-pore-size filter. The approximate numbers of CFU per gram are the sizes of the initial nocula. The signal ratio is the number of positive reactions versus the total number of reactions. + indicates that L. monocytogenes DNA was amplified in all six replicates performed in two independent experiments.