Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 19, 2006
Publication Date: October 1, 2006
Citation: Cooley, M.B., Chao, D.K., Mandrell, R.E. 2006. Escherichia coli O157:H7 survival and growth on lettuce is altered by the presence of epiphytic bacteria. Journal of Food Protection.69:10:2329-2335 Interpretive Summary: Several epidemics have been traced to pathogen contamination of produce. We have shown survival of a human pathogen on lettuce following seed inoculation and have isolated other bacteria naturally present on the plant. One of these bacteria competes with the pathogen and limits its survival. Another of these bacteria aids the survival of the pathogen.
Technical Abstract: Escherichia coli O157:H7 can survive in low numbers in soil and on plants. Occasionally conditions may occur in the field that lead to contamination of produce. Survival of enteric pathogens in the field is controlled to a certain extent by complex interactions with indigenous soil-borne and seed-borne epiphytes. Identifying these interactions may assist in developing strategies to improve produce safety. Two epiphytes were isolated from pathogen-contaminated plants that interact differently with E. coli O157:H7. Wausteria paucula enhanced the survival of E. coli O157:H7 six-fold on lettuce foliage grown from co-inoculated lettuce seed. In contrast, Enterobacter asburiae decreased E. coli O157:H7 survival 20 to 30-fold on foliage. Competition also occurred in the rhizosphere and in plant exudate. This competition may be the result of E. asburiae utilization of several of carbon and nitrogen substrates typically present in exudate and also used by E. coli O157:H7. Hence, competition observed on the plant may involve one or more nutrients provided by the plant. In contrast, a different mechanism may exist between E. coli O157:H7 and W. paucula since commensalism was only observed on foliage, not in the rhizosphere or plant exudate. Good agricultural practices that encourage the growth of competing bacteria, like E. asburiae, may reduce the incidence of produce contamination.