Factors That Affect Proliferation of Salmonella in Tomatoes Post-Harvest: The Roles of Seasonal Effects, Irrigation Regime, Crop and Pathogen Genotype

Abstract

Main ObjectivesFresh fruits and vegetables become increasingly recognized as vehicles of human salmonellosis. Physiological, ecological, and environmental factors are all thought to contribute to the ability of Salmonella to colonize fruits and vegetables pre- and post-harvest. The goal of this study was to test how irrigation levels, fruit water congestion, crop and pathogen genotypes affect the ability of Salmonella to multiply in tomatoes post-harvest.Experimental DesignFruits from three tomato varieties, grown over three production seasons in two Florida locations, were infected with seven strains of Salmonella and their ability to multiply post-harvest in field-grown tomatoes was tested. The field experiments were set up as a two-factor factorial split plot experiment, with the whole-plot treatments arranged in a randomized complete-block design. The irrigation treatment (at three levels) was the whole-plot factor, and the split-plot factor was tomato variety, with three levels. The significance of the main, two-way, and three-way interaction effects was tested using the (type III) F-tests for fixed effects. Mean separation for each significant fixed effect in the model was performed using Tukey’s multiple comparison testing procedure.Most Important Discoveries and SignificanceThe irrigation regime per se did not affect susceptibility of the crop to post-harvest proliferation of Salmonella. However, Salmonella grew significantly better in water-congested tissues of green tomatoes. Tomato maturity and genotype, Salmonella genotype, and inter-seasonal differences were the strongest factors affecting proliferation. Red ripe tomatoes were significantly and consistently more conducive to proliferation of Salmonella. Tomatoes harvested in the driest, sunniest season were the most conducive to post-harvest proliferation of the pathogen. Statistically significant interactions between production conditions affected post-harvest susceptibility of the crop to the pathogen. UV irradiation of tomatoes post-harvest promoted Salmonella growth.

Salmonella Persistence in Tomatoes Requires a Distinct Set of Metabolic Functions Identified by Transposon Insertion Sequencing

“…can proliferate within red ripe tomato pericarps, reaching ϳ10 7 CFU per fruit (9,19,21,25,35). To represent the entire transposon insertion library, the screening needed to be done using an inoculum titer very close to the carrying capacity of tomatoes.…”

“…Biosynthesis of amino acids was also a likely factor required for Salmonella growth in alfalfa root exudates (15). Plant colonization by Salmonella is affected by host factors; the genetic background can influence Salmonella colonization of sprouts (18), proliferation in the tomato phyllosphere (19,20), and pericarps (21).…”

Scientific Opinion on the risk posed by pathogens in food of non-animal origin. Part 2 (Salmonellaand Norovirus in tomatoes)

“…Very few research studies have evaluated the impact of seasonality on the proliferation of Salmonella in fresh produce. Marvasi et al (2013) found that the driest and sunniest seasons were the most conducive to post harvest proliferation of Salmonella and tomatoes. However, this study only identified an indirect effect of the climatic conditions as the seasonal effects were only evaluated on the post-harvest proliferation of Salmonella.…”

“…In addition to the quality of the irrigation water, irrigation practices in terms of amount of water may also affect the susceptibility of tomatoes to post-harvest Salmonella growth inside tomatoes. Marvasi et al (2013) reported that artificial soaking of tomato pericarp tissues in water caused a 10-fold increase of inoculated Salmonella growth. However, these authors could not reproduce such an increase of Salmonella growth by over irrigating field grown tomatoes.…”

Effect of the irrigation regime on the susceptibility of pepper and tomato to post-harvest proliferation of Salmonella enterica

“…Aristotle) and tomatoes Bonny Best and Solar Fire). All data for tomatoes of the three varieties were combined to serve as a broader basis for comparison, while a more comprehensive analysis of the responses of different tomato varieties to different irrigation regimes is reported elsewhere (Marvasi et al, 2013). As shown in Fig.…”