Comparison of samples positive for O157 STEC and non-O157 STEC by M1, M2 and M3 at corresponding sequential periods.

aDomestic ruminant samples includes cattle, alpaca, goat. Soil, designates soil next to leafy green plants predominantly. Water (ranch), designates samples of standing water or trough water on a livestock ranch. Water (farm), designates irrigation, standing or creek/stream water on a leafy greens produce farm. Water (watershed), designates water from the Salinas River and tributaries and other watershed sites with public access.
bWater (farm), designates farms growing leafy greens.
cNine of the 10 O157 positive samples were isolated from very dry soil collected in a cattle ranch pasture.
dFive of the non-O157 STEC-positive produce samples were identified by screening by M3 additional suspect colonies from a sample of the saved frozen TSB enrichment broths.