ARS | Publication request: A comparison of E. coli persistence on basil plants and soil using drip and overhead irrigation

Submitted to: International Association for Food Protection
Publication Type: Abstract Only
Publication Acceptance Date: March 6, 2012
Publication Date: July 22, 2012
Citation: Markland, S., Shortlidge, K., Cook, L., Lestrange, K., Sharma, M., Kniel, K. 2012. A comparison of E. coli persistence on basil plants and soil using drip and overhead irrigation. International Association for Food Protection. [abstract].

Technical Abstract: Introduction: It is estimated that each year in the US there are 63,153 cases of foodborne illnesses caused by E.coli O157 serotypes and 112,752 illnesses caused by non-O157 shiga-toxin producing E.coli. Irrigation water is recognized as a pre-harvest contamination source and has been linked with outbreaks of E. coli O157:H7 on leafy greens. Purpose: In this study, the persistence of E. coli O104:H4, E. coli O157:H7 4407, and a cocktail of avian pathogenic E. coli O157 serotypes (APEC) on basil plants and soil using drip and overhead irrigation models was investigated. Methods: Overnight cultures were individually inoculated into an irrigation solution containing dairy and poultry manure slurry. Soil was inoculated with 3 mL of irrigation solution by pipette to model drip irrigation. Plants were sprayed with irrigation solution using an airbrush for 20 s (3 mL) to model overhead irrigation and resulted in 5.3, 5.8, and 5.3 log CFU/plant of E.coli O157:H7, E.coli O104:H4, and APEC on day 0, respectively. Plant and soil samples were taken on days 0 through 4 and bacterial populations were enumerated on selective media. Results: E. coli were not detected on whole plants inoculated by drip irrigation. When overhead-inoculated by spray, bacteria persisted on plants at significantly higher populations (p=0.03; a<0.05) with 2.3, 3.8, and 4.8 log CFU/plant of E.coli O157:H7, E.coli O104:H4, and APEC detected on plants 4 d post-inoculation, compared to persistence on drip-irrigated plants. Environmental APEC strains were recovered at significantly higher populations than outbreak strains on plants. Significance: E. coli O157 serotypes and E. coli O104 did not persist on plants as readily as they did in soil. Environmental APEC persisted at higher populations than outbreak strains on basil plants. This study reinforces the notion that drip irrigation reduces the risk of contamination on foliar surfaces.