Investigation of potential reservoirs of shiga toxin-producing E. coli and Salmonella in produce production areas of Arizona and Mexico. (rapid response)

Investigation of potential reservoirs of shiga toxin-producing E. coli and Salmonella in produce production areas of Arizona and Mexico. (rapid response)

Oct. 5, 2010 - Apr. 30, 2011

2011-RR1

$70,567.00

Michele Jay-Russell, Ph.D.
University of California, Davis

Final Report

In May 2010, Romaine lettuce grown in Arizona was implicated as the vehicle in a multi-state
outbreak of E. coli O145 infections. This is the first known leafy green-related shiga toxinproducing
Escherichia coli (STEC) outbreak traced to the Yuma production region. Pre-harvest
contamination was suspected, but the source of the outbreak was not definitively determined.
The long-term goal of this project is to identify potential domestic and wild animal reservoirs of
foodborne pathogens in produce production regions of Arizona and Northern Mexico. In the first
“emergency response” phase of the project we are determining if free-roaming domestic dogs
and coyotes in these regions shed STEC and/or Salmonella enterica in their feces. We focused
on canids based on feedback from growers who reported that unleashed, free-roaming
domestic dogs and coyotes are common in this region. Intrusions into produce fields have
resulted in damage to leafy greens and other crops, but the food safety risk from stray dogs and
coyotes is unclear. To address this gap in knowledge, we conducted a study during the 2010-
2011 southwestern desert growing season to assess foodborne pathogen carriage in stray dogs
and coyotes. In a unique industry-university partnership, the produce company managed the
field activities including specimen collection and shipping, while UC Davis investigators
conducted laboratory and data analyses. Three animal shelters were enrolled in the study and
visited monthly to sample fresh feces from dogs recently impounded. Fresh coyote scat was
collected at dawn by walking the dirt roads near produce fields. Samples were shipped from
Yuma to Davis overnight and processed within 24 hours. Standard culture methods were used
to isolate STEC and Salmonella. No shiga toxin-producing E. coli was identified among 473
samples, although 8 E. coli isolates belonging to serogroups O26, O145, or O157 were positive
for other virulence determinants by PCR (eae, hylA) suggesting the potential to be a human
pathogen. Overall, Salmonella was cultured from 33 (9.2%) of 358 dog fecal samples
compared with 33 (32%) of 103 coyote scat samples. Twenty-nine Salmonella serotypes were
identified including types that have been associated previously with human illness.