Tomato type, maturity and seasonal variability are the strongest factors affecting the ability of Salmonella to multiply in the fruit post-harvest.
Out of the factors looked at it remains unclear how much each contributes but a better understand of each one’s role could lead to a reduction in the number or severity of produce-associated outbreaks.
The goal of the University of the Florida 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.
Red ripe tomatoes were significantly and consistently more conducive to proliferation of Salmonella, found Marvasi et al.
Tomatoes harvested in the driest, sunniest of the seasons were the most conducive and blemish-free tomato fruits displaying symptoms of bacterial spot were less conducive to proliferation.
Artificially congesting green tomato fruits with water led to ~1 log increase in Salmonella proliferation. However, changes in the irrigation regime imposed within two to four weeks of harvest had no observable effect on the susceptibility of tomato fruits to post-harvest proliferation.
Fruits 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.
Harvested tomatoes were brought into the lab and inoculated with Salmonella typically within 2–24 hours of the harvest.
The rationale was based on models of plant disease, which suggest that varying the intensity of irrigation has significant effects on the susceptibility of crops to phytopathogens, as well as their persistence in the environment.
Even though Salmonella is not a plant pathogen, the researchers hypothesized that similar mechanisms may underlie its interactions with plants.
Tomatoes vulnerability to contamination by Salmonella is being studied by scientists at the US Food and Drug Administration (FDA).
From 1973 to 2010, there were 15 multistate outbreaks of illnesses attributed to Salmonella contamination of raw tomatoes, with 12 of these outbreaks taking place since 2000.
They resulted in almost 2,000 confirmed illnesses and three deaths, with states in the eastern US hardest hit, said the agency.
FDA is working with the Environmental Protection Agency (EPA) to develop an organic treatment containing Paenibacillus that would kill Salmonella and other harmful organisms.
The University of Florida research was supported by a USDA NIFA-AFRI grant and funding from the Center for Produce Safety and Florida Specialty Crops Foundation.
Source: PLOS ONE
Online ahead of print, doi: 10.1371/journal.pone.0080871
“Factors That Affect Proliferation of Salmonella in Tomatoes Post-Harvest: The Roles of Seasonal Effects, Irrigation Regime, Crop and Pathogen Genotype”
Authors: Massimiliano Marvasi, George J. Hochmuth, Mihai C. Giurcanu, Andrée S. George, Jason T. Noel, Jerry Bartz, Max Teplitski