Are soil negatives related to sample number or size?
Soil sample size for testing was always 25 g. A negative soil sample refers to a non-detection of STEC in 25 g of soil.
Soil prevalence data was presented as STEC. Was this based on stx only or also ear and additional clinically relevant sequences?
For this study, STEC detection was based on the presence of stx genes in the recovered isolates. All isolates were sequenced and the sequencing data will be uploaded in NCBI pathogen database.
For the 4 transects in terms of microbiome - was the difference performed by Anova, meaning that 1 was different from the other three, or pairwise comparison?
PERMANOVA was used for statistical comparisons of microbiomes. These data are currently being analyzed with plans to publish a manuscript in 2026 or 2027. The data will be presented as a poster at the annual meeting of the International Association of Food Protection (IAFP). The abstract will be available then.
Susan R. Leonard, Cassandra Champ, Anne-Laure Moyne, Mark K. Mammel, Xiaohong Wei, Peiman Aminabadi, Carter Palen, David W. Lacher, Eric W. Brown, Michele Jay-Russell, Edward R. Atwill, Linda J. Harris. Environmental Drivers of Soil Microbiome and Shiga Toxin-Producing Escherichia coli Presence in a California Central Coast Fresh Produce Field. (Abstract #T8-01). Tuesday, July 28, 2026. Annual IAFP meeting 2026, New Orleans, LA, July 26-29.
How can we assert soil is not reservoir when clusters are observed?
Detection of STEC in soil samples does not necessarily establish soil as a long-term reservoir. In this study, STEC isolation from field soils was generally low, although somewhat higher frequencies were observed during or following flooding events in at least one field. In addition, STEC detected in soil could result from multiple inputs, including wildlife or livestock fecal deposition. Many of the STEC positive soil samples that were not flood-related were not isolated in temporal clusters.
Positives after one month of flooding events- was there any indication as to the length of time necessary after a flooding event needed for risk reduction?
No. We did not design the study to address this specific question.
Regarding flooding…How did the researchers define “during flood events” and “post flood events”? For example, during flooding did soil samples get taken when water is still present?
“Flood events” were defined as periods when heavy rainfall and/or the Salinas River caused partial or complete submergence of a collaborating produce field. When conditions allowed (i.e., fields were accessible), some soil samples were collected while standing water was still present. “Post-flood events” were defined as subsequent sampling periods after floodwaters had receded and fields were no longer submerged.
Transect = where wildlife travel between rangeland and riparian habitat?
No. In this study, transects refer to fixed lines established along rows of crops (e.g., vineyards or row crops) that spanned from one landscape feature (such as rangeland) to another (such as riparian habitat). These transects defined consistent locations where soil samples were collected during each sampling event. They do not represent wildlife travel paths, but rather standardized sampling routes across different landscape interfaces.