Colonization of Tomato Plants by <i>Salmonella enterica</i> Is Cultivar Dependent, and Type 1 Trichomes Are Preferred Colonization Sites

Abstract

Nontyphoid salmonellosis caused by Salmonella enterica is the most common bacterial food-borne illness in humans, and fresh produce, including tomatoes, is a common vehicle. Accumulating data indicate that human enteric pathogenic bacteria, including S. enterica, interact actively with plants. Tomato plants were inoculated with S. enterica to evaluate plausible contamination routes and to determine if the tomato cultivar affects S. enterica colonization. S. enterica population levels on tomato leaves were cultivar dependent. S. enterica levels on Solanum pimpinellifolium (West Virginia 700 [WVa700]) were lower than on S. lycopersicum cultivars. S. enterica preferentially colonized type 1 trichomes and rarely interacted with stomata, unlike what has been reported for cut lettuce leaves. Early S. enterica leaf colonization led to contamination of all fruit, with levels as high as 10(5) CFU per fruit. Reduced bacterial speck lesion formation correlated with reduced S. enterica populations in the phyllosphere. Tomato pedicels and calyxes also harbored large S. enterica populations following inoculation via contaminated water postharvest. WVa700 green fruit harbored significantly smaller S. enterica populations than did red fruit or S. lycopersicum fruit. We found that plants irrigated with contaminated water had larger S. enterica populations than plants grown from seeds planted in infested soil. However, both routes of contamination resulted in detectable S. enterica populations in the phyllosphere. Phyllosphere S. enterica populations pose a risk of fruit contamination and subsequent human disease. Restricting S. enterica phyllosphere populations may result in reduced fruit contamination. We have identified WVa700 as a tomato cultivar that can restrict S. enterica survival in the phyllosphere.