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P1-16 Rainfall Promotes Growth of Fecal Coliforms in Soil and on Leafy Greens during Production in the Mid-Atlantic Region of the United States

Monday, August 1, 2016
America's Center - St. Louis
Mary Theresa Callahan, University of Maryland, College Park, MD
Patrick Spanninger, University of Delaware, Newark, DE
Jennifer Todd-Searle, Rutgers University, New Brunswick, NJ
Sasha Marine, University of Maryland, Salisbury, MD
Justine Beaulieu, University of Maryland, College Park, MD
Meredith Melendez, Rutgers New Jersey Agricultural Experiment Station, Millville, NJ
Wesley Kline, Rutgers New Jersey Agricultural Experiment Station, Millville, NJ
Donald W. Schaffner, Rutgers University, New Brunswick, NJ
Kali Kniel, University of Delaware, Newark, DE
Christopher Walsh, University of Maryland, College Park, MD
Kathryne Everts, University of Maryland, Salisbury, MD
Robert Buchanan, University of Maryland, College Park, MD
Shirley A. Micallef, University of Maryland, College Park, MD
Introduction: Previous field studies have reported increases in recovery of fecal coliforms (FC) from produce after a rain event. It is unclear whether this is a consistent occurrence, and how long increased population levels persist on crops.  Enhanced bacterial growth following rainfall signals a possible food safety risk and would have significant implications for harvesting practices.

Purpose: This study evaluated the effect of rainfall events on naturally-occurring FC populations in soils and on leafy greens being cultivated on commercial farms.

Methods: For three days following significant rainfall (>1.3 cm rainfall within 24 h), leafy green and soil samples (5 replicates each) were collected from farms in Maryland, Delaware and New Jersey. Escherichia coli and FC were enumerated by direct plate counts on TBX agar. Samples were also collected before rainfall to determine baseline populations of these microorganisms. Data were collected surrounding rainfall events occurring during the spring and fall growing seasons of 2015.

Results: On central Maryland and Maryland eastern shore farms, a significant increase in recovery of FC was observed in both soil and on leafy greens after rainfall in fall (P<0.05) but not spring. A similar increase in recovery occurred in fall for farms in central and southern New Jersey (P<0.05). In Delaware, FC populations in soil remained constant before and after rain, but an increase in FC levels in leafy greens samples was observed in spring, although the effect was not significant. In all regions, recovery of E. coli was too low or sporadic to determine a significant effect of rain.

Significance: Following rain, FC populations surged in soil and on leafy greens during production, especially in fall.  Levels returned to baseline within two days.  Harvesting delays following rain may reduce any potential microbial food safety risk posed by rainfall for leafy greens.

Back to: Poster Session 1 – Produce, Meat, Poultry and Eggs, Non-microbial Food Safety; Laboratory and Detection Methods; Communication Outreach and Education; Seafood; Antimicrobials; Food Toxicology
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