Skip to main content
ARS Home » Pacific West Area » Albany, California » Western Regional Research Center » Produce Safety and Microbiology Research » Research » Publications at this Location » Publication #305892

Title: Male-specific coliphages for source tracking fecal contamination in irrigation waters and prevalence of Shiga toxigenic Escherichia coli in a major produce production region of central coast of California

item Ravva, Subbarao
item Sarreal, Chester
item Cooley, Michael - Mike

Submitted to: Environmental Science: Processes & Impacts
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/12/2015
Publication Date: 10/9/2015
Citation: Ravva, S.V., Sarreal, C.Z., Cooley, M.B. 2015. Male-specific coliphages for source tracking fecal contamination in irrigation waters and prevalence of Shiga toxigenic Escherichia coli in a major produce production region of central coast of California. Environmental Science: Processes & Impacts. doi: 10.1039/C4EM00537F.

Interpretive Summary: Major outbreaks associated with produce indicate that pre-harvest contamination has occurred in the field, so it is critical to identify and track sources of pathogens in the environment and interventions for minimizing them. Since contamination of ‘ready to eat’ produce cannot be washed off, on-site prevention of contamination is vital. Any such attempts require an understanding of the biological and environmental factors that regulate the proliferation of pathogens during their transport from animal reservoirs to produce grown in proximity to livestock operations. We have worked on developing improved detection methods for pathogens, and on understanding how pathogens survive, transport and re-grow in agricultural environments. Our long-term goals are to develop on-site prevention and control of pathogens at the source prior to contaminating produce we consume. Given that dairy and feed-lot cattle are considered sources or carriers of E. coli O157 and other Shiga-toxigenic pathogens, determining the sources of fecal contamination appear to be a less resource intensive alternative to tracking the target pathogen. We developed a real-time reverse-transcriptase PCR method to track coliphages specific for human and animal sources. We identified coliphages from human impacted sites are primary contaminants in irrigation waters in Salinas Valley during the winter months. Animal contribution to contamination was minor in comparison. Similar studies will be expanded to include additional produce production regions, areas influenced by animal raising operations and human-impacted sites should provide valuable data that aids in controlling or minimizing the spread of E. coli O157 and other enteric pathogens.

Technical Abstract: Determining the environmental sources for Shiga toxigenic Escherichia coli is of paramount importance. Since dairy or feedlot cattle are likely sources for this pathogen, determining the sources of fecal contamination may provide supplemental data to traditional trace-back studies from fork to farm. We developed quantitative reverse-transcriptase PCR methods to determine the prevalence of F+ RNA coliphages (FRC) as indicators of fecal contamination. Male-specific coliphages, determined using single agar overlay method, were prevalent in all irrigation water samples collected during 8 months of sampling. Majority (90%) of the FRC characterized were sourced to humans and originated from human-impacted sites. Members of genogroup III represented 77% of FRC originated from human sources. Furthermore, 93% of FRC sourced to animals were also detected in waters from human-impacted sites. Eighty percent of all FRC were isolated during the winter months indicating seasonality in prevalence. Rain events could not be correlated with the prevalence of male-specific coliphages, FRC, E. coli O157:H7 or shiga-toxigenic E. coli in waters. Both coliform bacteria and generic E. coli from agricultural or human-impacted sites were similar in numbers and thus could not be used to determine sources of fecal contamination. We propose data on male-specific coliphages and FRC may not be a good indicator for predicting the sources of fecal contamination and aid in preventing or controlling the spread of enteric pathogens from likely sources.