. 2013 Jun 6;8(6):e65716. doi: 10.1371/journal.pone.0065716

Table 3. RT-PCR with and without Environmental Master Mix (EMM) to detect stx genes in environmental sample enrichments spiked with STEC.

Sample Type^a	Treatment	Samples (N)	Average CFU/mL (X10⁶) at Ct 27 (SD)^b
Soil	None	5	>10.7 (6.7)^B
Soil	EMM	5	3.1 (3.0)^A
Water	None	7	3.8 (3.2)^A
Water	EMM	7	3.4 (3.2)^A
Lettuce	None	3	3.1 (3.7)^A
Lettuce	EMM	3	3.4 (4.0)^A
Feces	None	6	>12.7 (7.6)^B
Feces	EMM	6	3.5 (3.5)^A

Lettuce = Iceberg; Water = surface water; Feces = cattle feces. Plants and soil were collected from coded farm location F; Cattle feces were collected from coded ranch location Q. Surface water was collected locally (37.882855 N, 122.300007 W). All samples tested as STEC-negative prior to spiking.

Enrichments were spiked with 10 fold dilutions of E. coli O157 strain RM1484 (0–20×10⁶ CFU/mL) and subjected to RT-PCR using AmpliTaq Gold or EMM (see Methods). Each of the samples produced a Ct, except for several soil and feces samples lacking a Ct even at the highest inoculum. A Ct of 27 corresponds to the upper limit we have set for culturing enrichment samples for isolation of STEC. SD, standard deviation. Different letter superscripts designate samples with a significant difference in treatment results (P<0.05).