|ZHU, LEI - University Of Arizona|
|RAVISHANKAR, SADHANA - University Of Arizona|
|JORGE, FONSECA - Food & Agriculture Organization (FAO)|
Submitted to: Journal of Agriculture & Life Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2015
Publication Date: 6/5/2015
Citation: Zhu, L., Juneja, V.K., Ravishankar, S., Jorge, F. 2015. Survival of Escherichia coli O157:H7 on lettuce harvested from fields irrigated by different irrigation systems and stored under different conditions. Journal of Agriculture & Life Sciences. www.jalsnet.com/journals/Vol-2-No-1-June-2015/2.
Interpretive Summary: Irrigation water may be a source of leafy greens contamination with deadly bacterium, Escherichia coli O157:H7. We determined the effect of drip, furrow and sprinkler irrigation system on survival of the pathogen on lettuce. Our findings suggest that, regardless of the irrigation system, E. coli O157:H7 can survive and grow to similar levels on both iceberg and romaine lettuce. Regulatory agencies will use these findings as a building block for risk assessment of E. coli O157:H7 on lettuce.
Technical Abstract: Escherichia coli O157:H7 outbreaks associated with the consumption of leafy greens have increased food safety concerns in the food industry. Irrigation water could be a major potential source of microbial contamination to vegetables. The potential for irrigation water to contaminate vegetables with E. coli O157:H7 could partially be dependent on the irrigation method used. The objective of this study was to investigate the survival of E. coli O157:H7 on iceberg and romaine lettuces harvested from fields irrigated using drip, furrow and sprinkler irrigation systems and stored under environmental conditions simulating the growing regions. Leaves of romaine or iceberg lettuce were inoculated with E. coli O157:H7 (6-7 log CFU/g) and stored under 3 different conditions of temperature and relative humidity (RH) combinations (26 degrees C, 40% RH; 10 degrees C, 60% RH and 4 degrees C, 60% RH) for 10 days. Both young and mature lettuces were tested. Samples were taken at day 0, 1, 2, 5, 7 and 10 to enumerate the surviving E. coli O157:H7 populations. Similar results were obtained for lettuce harvested from fields irrigated using the 3 irrigation systems. E. coli O157:H7 population increased 2-3 logs and 1-2 logs when the leaves were stored at 26 degrees C, 40% RH and 10 degrees C, 60% RH, respectively. There was no change in E. coli O157:H7 population when stored at 4 degrees C, 60% RH. The results showed similar survival patterns on both romaine and iceberg lettuces. The population of E. coli O157:H7 on mature lettuce was 0.5 log higher than that on baby lettuce after day 5 when stored at 26 degrees C, 40% RH. This study showed that irrespective of the irrigation system used in the field, E. coli O157:H7 can survive/grow to similar levels in lettuce, when the contamination occurs during postharvest stages. These results will form a supporting basis for risk assessment of E. coli O157:H7 on lettuce.