Fate of Escherichia coli O145 present naturally in bovine slurry applied to vegetables before harvest, after washing and simulated wholesale and retail distribution

Aims: To determine the fate of Escherichia coli on vegetables that were processed through commercial wash treatments and stored under simulated retail conditions at 4 degrees C or wholesale at fluctuating ambient temperatures (0-25 degrees C, dependent on season). Methods and Results: Bovine slurry that was naturally contaminated with E.coli O145 was applied without dilution or diluted 1:10 using borehole water to growing potatoes, leeks or carrots. Manure was applied 1week prior to harvest to simulate a near-harvest contamination event by manure deposition or an application of contaminated water to simulate a flooding event or irrigation from a contaminated water source. At harvest, crops were contaminated at up to 2 log cfu g(-1). Washing transferred E.coli into the water of a flotation tank used for potato washing and did not completely remove all traces of contamination from the crop. Manure-contaminated potatoes were observed to contain 0.72 cfu E.coli O145 g(-1) after processing and retail storage. Manure-contaminated leeks harboured 0.73-1.55 cfu E.coli O145 g(-1) after washing and storage. There was no cross-contamination when leeks were spray washed. Washing in an abrasive drum resulted in less than perfect decontamination for manure-contaminated carrots. There were five post-distribution isolations from carrots irrigated with contaminated water 24h prior to harvest. Conclusions: Standard commercial washing and distribution conditions may be insufficient to reliably control human pathogenic E.coli on fresh produce. Significance and Impact: Previous speculation that the cause of a UK foodborne disease outbreak was soil from imperfectly cleaned vegetables is plausible.