A recent study demonstrated that wild animal poop (aka scat) can serve as a source of E.coli O157:H7 for produce located in close proximity. In the study, rabbit poop inoculated with E.coli was placed ina romaine lettuce field, the field was irrigated ("foliar irrigation by using typical commercial farming practices for central coastal California"), the lettuce was tested, and 38 of the lettuce had E. coli. Some good news however, removing the out leaves of lettuce was effective at eliminating the contamination.
Romaine study examines wildlife, E. coli
By Mike Hornick February 24, 2015 | 5:47 pm EST
Growers’ removal of wildlife feces from their fields has gained confirmation from a study that supplies new data about how much E. coli O157:H7 can be transferred to romaine from that source by foliar irrigation.
The joint study by Western Center for Food Safety and Food and Drug Administration researchers, published in the February Journal of Food Protection, also aims to provide insights for emerging food safety strategies.
Its findings are based on a 2011 trial in California’s Salinas Valley using E. coli-spiked rabbit feces. Immediately after irrigation, 168 lettuce heads at varying distances were collected. Of those, 38% had detectable E. coli O157:H7 — albeit at a much reduced concentration.
Few prior studies had been done to quantify the microbial load transferred from soil or wildlife feces onto produce during irrigation.
“Basically, we were hoping that this field trial would generate real-world field data to support the common practice of removing scat from the furrows, especially prior to final irrigation,” said Rob Atwill, principal investigator for the Western Center for Food Safety at the University of California, Davis.
“Interestingly, no heads of lettuce were found to have this bacteria when the outer leaves are trimmed off,” Atwill said. “So this standard industry practice of trimming the outer leaves appears to be a key food safety step, which most folks already assumed to be true. What we are thinking now is, can the nozzle from an impact sprinkler be modified to minimize fecal splash but still deliver an appropriate amount of irrigation water – say, in high winds?”
He is one of the study’s nine authors. They conclude that data from such trials can be used to aid quantitative risk assessment for E. coli in romaine and to develop “effective, on-farm intervention strategies for produce.”
Journal of Food Protection
Transfer of Escherichia coli O157:H7 from Simulated Wildlife Scat onto Romaine Lettuce during Foliar Irrigation
EDWARD R. ATWILL,1* JENNIFER A. CHASE,1 DAVID ORYANG,2 RONALD F. BOND,1 STEVEN T. KOIKE,3 MICHAEL D. CAHN,3 MAREN ANDERSON,4 AMIRHOSSEIN MOKHTARI,4 AND SHERRI DENNIS2
1Western Center for Food Safety, University of California at Davis, 1477 Drew Avenue, Suite 101, Davis, California 95618; 2Center for Food Safety and Applied Nutrition, U.S. Food and Drug Administration, 5100 Paint Branch Parkway, College Park, Maryland 20740; 3University of California Cooperative Extension Monterey County, 1432 Abbott Street, Salinas, California 93901; and 4RTI International, 3040 East Cornwallis Road, Research Triangle Park, North Carolina 27709, USA
MS 14-277: Received 10 June 2014/Accepted 3 October 2014
A field trial in Salinas Valley, California, was conducted during July 2011 to quantify the microbial load that transfers from wildlife feces onto nearby lettuce during foliar irrigation. Romaine lettuce was grown using standard commercial practices and irrigated using an impact sprinkler design. Five grams of rabbit feces was spiked with 1.29 | 108 CFU of Escherichia coli O157:H7 and placed 23, 22, and 21 days and immediately before a 2-h irrigation event. Immediately after irrigation, 168 heads of lettuce ranging from ca. 23 to 69 cm (from 9 to 27 in.) from the fecal deposits were collected, and the concentration of E. coli O157:H7 was determined. Thirty-eight percent of the collected lettuce heads had detectable E. coli O157:H7, ranging from 1 MPN to 2.30 | 105 MPN per head and a mean concentration of 7.37 | 103 MPN per head. Based on this weighted arithmetic mean concentration of 7.37 | 103 MPN of bacteria per positive head, only 0.00573% of the original 5 g of scat with its mean
load of 1.29 | 108 CFU was transferred to the positive heads of lettuce. Bacterial contamination was limited to the outer leaves of lettuce. In addition, factors associated with the transfer of E. coli O157:H7 from scat to lettuce were distance between the scat and lettuce, age of scat before irrigation, and mean distance between scat and the irrigation sprinkler heads. This study quantified the transfer coefficient between scat and adjacent heads of lettuce as a function of irrigation. The data can be used to populate a quantitative produce risk assessment model for E. coli O157:H7 in romaine lettuce to inform risk management and food safety policies.