Table 3.

Samples analyzed.

Concentration Range	N	DNA Extraction Protocol
		Thermal	Chelex	Beads	GM	ISO
4	1	+	+	+	+	+
3	2	+	+	+	+	+
2	2	+	+	+	+	+
1	6	+	+	+	5	+
<1	16	8	7	4	6	8
NS	2	-	-	-	-	-
HPI	2	+	+	+	+	+
LPI	2	+	+	+	+	+
NI	2	-	-	-	-	-

Concentration range values expressed as “log CFU/ sample”. “N”: number of samples. A “+” or “-” denotes that all the samples were either positive or negative; alternatively, if a number is provided, it indicates the number of positive samples. “ISO” refers to the reference method ISO 6579-1:2017. “NS”: not spiked. “HPI”: high positive interlaboratory samples (57 CFU). “LPI”: low positive interlaboratory samples (10 CFU). “NI”: negative interlaboratory samples.