RT-PCR with and without Environmental Master Mix (EMM) to detect <i>stx</i> genes in environmental sample enrichments spiked with STEC.

aLettuce = 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. bEnrichments 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).