Pre-harvest Microbial Contamination of Tomato and Pepper Plants: Understanding the Pre-harvest Contamination Pathways of Mature Tomato and Bell Pepper Plants Using Bacterial Pathogen Surrogates

Seelavarn Ganeshan and Hudaa N

Abstract

Tomatoes and bell peppers have been previously incriminated in outbreaks of foodborne illnesses due to contamination by human pathogens such as E. coli O157:H7 and Listeria monocytogenes in the field. The objectives of the present study were to investigate (i) the potential entry of E. coli (EC) and L. innocua (LI) from soil to various non-edible and edible parts of the tomato and pepper plants, and (ii) the ability of EC and LI to survive in the plant environment (soil, rhizosphere and phyllosphere). Mature tomato and bell pepper plants cultivated in a greenhouse were soil-inoculated with a bacterial suspension (ca. 108 cfu/ml) of EC or LI. Tomatoes and peppers were also artificially contaminated on the surface with 1 ml of an overnight culture of EC and LI (ca. 109 cfu/ml). Samples of vegetables as well as non-edible parts (soil, roots, stem, foliage) were subjected to microbiological analyses by plating on Eosin Methylene Blue Agar and Listeria Identification Agar to recover EC and LI respectively. Although these bacteria were recovered at population densities of 3.0-3.6, 1.8-2.2 and <0.7 log cfu/g in the bulk soil, roots and foliage respectively, we were unable to recover these bacteria from the edible tomato and pepper fruits. When tomatoes and peppers were spot-inoculated on the surface with EC or LI, the vegetables analyzed were shown to harbor viable bacterial cells for up to 48 h after inoculation. Overall, the potential for systemic uptake and translocation of human pathogens from soil to the edible plant parts was found to be negligible in tomato and pepper plants. However, overhead (spray or sprinkler) irrigation with contaminated water could create opportunities for the deposition and subsequent persistence of human pathogens on the edible surface of vegetables even after harvest. These findings therefore underscore the need for adoption of Good Agricultural Practices (GAPs) by growers and Good Manufacturing Practices (GMPs) by post-harvest handlers of fresh produce.