The ecology of the vegetable leaf surface is important to the survival of enteric pathogens. Understanding changes in ecological parameters during the preharvest stages of production can lead to development of approaches to minimize the hazard of contamination of fresh fruits and vegetables with foodborne pathogens. In this study, survival levels of Escherichia coli O157 over a 10-day period were compared among traumatically injured, phytopathogen-damaged, and healthy lettuce plants. Leaves from lettuce plants cracked along the central vein, plants infected with Xanthomonas campestris pv. vitians, and healthy plants were inoculated with E. coli O157:H7. The presence of E. coli O157:H7 populations on inoculated leaves and non-inoculated leaves of these same plants was determined for 10 days. The density of E. coli O157:H7 decreased over time on the inoculated leaves regardless of the treatment. The population of E. coli O157:H7 remained higher on traumatically injured leaves than on healthy plants (P < 0.001). E. coli O157:H7 was detected on leaves other than the direct inoculation site of the enteric pathogen in all three treatments groups. Preharvest damage, especially that caused by traumatic injury, impacted the survivability of E. coli O157:H7. Maintaining healthy plants and minimizing physical damage around the time of harvest might improve the safety of fresh produce.

Pathogens on edible plants present a significant potential source of human illness. From 1991 to 2002, 21% of Escherichia coli O157:H7 outbreaks were from produce-related sources. E. coli O157 and other enteric bacteria can contaminate the surface of edible plants both pre-and postharvest. Some pathogens do not survive on the leaf surface or are removed by washing, but a significant portion of these enteric pathogens can persist on the surface and proliferate. Proliferation of these dangerous pathogens can increase the likelihood of foodborne disease associated with fresh or minimally processed produce. Several intrinsic and extrinsic factors determine the ability of enteric pathogens to attach and proliferate in the phyllosphere of plants. These include motility of the pathogen, leaching of nutrients by the plant, and interaction with epiphytic organisms. The interaction of enteric pathogens with the environment can lead to internalization into tissue, incorporation into biofilms, and genetic transfer. Current produce sanitation practices can reduce the microbial load from 1 log 10 to 3 log 10 , so there are many new treatments possible. Understanding the ecology of enteric pathogens on plants is important to the development of sanitation methods and biocontrol agents. This knowledge can also assist the farmer in preventing contamination. With increasing consumption and importation of produce, its safety is a high priority for processors and U.S. consumers. Food safety may be markedly improved with proper attention to pathogens on edible plants.

The survival of enteric pathogens on vegetable leaves improves due to presence of phytopathogens. Phytopathogen damage alters the microenvironment on the leaf surface. The objective of this study was to identify differences in sugar concentrations in tomato leaves damaged by biotropic plant pathogens and determine if these differences affect Escherichia coli O157:H7 survival. E. coli O157:H7 survived better on tomato plants damaged by Xanthomonas campestris than on healthy plants (P = 0.012). The most common sugars and sugar alcohols in the damaged leaf exudate were glucose, fructose, inositol, and sucrose. The abundance of sucrose and inositol differed between the healthy and infected plants (P < 0.05). In this study, it was found that phytopathogen damaged plants increased sugar availability on the leaf surface for E. coli O157:H7 to proliferate. Keeping plants free from biological damage can limit the amount of leaching of sugars that could allow human pathogens to proliferate. There is the possibility of increasing food safety of vegetable products by limiting phytopathogenic damage to plants.