Persistence of Escherichia coli on injured vegetable plants

Minor shoot injury to glasshouse celery, Cos lettuce and chive plants significantly increased the persistence of applied Escherichia coli (P<0.05). After 1 week, mean counts of about 5 log(10) CFU/g decreased to fewer than 0.5 log(10) CFU/g on the uninjured plants, compared to 4 log(10) CFU/g or more on injured plants. By the end of the 3-week long experiments, counts from the uninjured plants were 0.21 log(10) CFU/g or fewer, but 2.8, 2.3 and 5.1 log(10) CFU/g on injured Cos lettuce, celery and chive plants, respectively. A field experiment using Cos lettuce also showed that shoot injury increased E. coli persistence. Counts from the injured plants on days 1, 3, and 7 were, 4.2, 4.1 and 3.3 log(10) CFU/g, respectively, whereas the uninjured plants returned significantly (P<0.05) lower counts on those days, and were 2.8, 2.0 and 1.2 log(10) CFU/g, respectively. These findings reveal that increased E. coli persistence on injured tissue is common to different vegetables and can occur in the glasshouse and the field. The implications of this study on vegetable production practices are presented.