A Fast, Reliable, and Sensitive Method for Detection and Quantification of Listeria monocytogenes and Escherichia coli O157:H7 in Ready-to-Eat Fresh-Cut Products by MPN-qPCR

Table 2

Quantification of L. monocytogenes and E. coli O157:H7 in artificially inoculated fresh-cut salads by MPN and confirmation of positive tubes by conventional methods and qPCR.

	Theoretical inoculum; (CFU g^−1)	3-tube dilution^1; (mL homogenized)	Positive tubes; (MPN)	True positive^2	MPN (g^−1)^3; (95% c.i.)	Positive; (qPCR)
L. monocytogenes	Control	10/1/0.1	0/0/0	n.d.	n.d.	n.d.
	1	10/1/0.1	3/2/0	3/2/0	0.93 (0.23–3.80)	3/2/0
	10	1/0.1/0.01	3/1/0	3/1/0	4.3 (0.90–18)	3/1/0
	100	0.1/0.01/0.001	3/0/2	3/0/2	64 (17–180)	3/0/2
	1000	0.01/0.001/0.001	3/1/1	3/1/1	750 (170–2000)	3/1/1
E. coli O157:H7	Control	10/1/0.1	3/3/3	n.d.	n.d.	n.d.
	1	10/1/0.1	3/3/3	3/1/2	>11.0	3/1/2
	10	1/0.1/0.01	3/3/1	3/2/0	46 (9–200)	3/2/0
	100	0.1/0.01/0.001	3/2/1	3/1/1	150 (37–420)	3/1/1
	1000	0.01/0.001/0.001	3/2/0	3/2/0	930 (180–4200)	3/2/0

1The reported dilution is referred to as the set of tubes considered for MPN enumeration.
²Confirmed by biochemical and immunological methods.
³Calculated on the basis of the true positive samples.