Abstract
Consumption of cucumbers (Cucumis sativus var. sativus) has been linked to several foodborne outbreaks involving Salmonella enterica. The purpose of this work was to investigate the efficiency of colonization and internalization of S. enterica into cucumber plants by various routes of contamination. Produce-associated outbreak strains of Salmonella (a cocktail of serovars Javiana, Montevideo, Newport, Poona, and Typhimurium) were introduced to three cultivars of cucumber plants (two slicing cultivars and one pickling) via blossoms (ca. 6.4 log10 CFU/blossom, 4.5 log10 CFU/blossom, or 2.5 log10 CFU/blossom) or soil (ca. 8.3 log10 CFU/root zone) and were analyzed for prevalence of Salmonella contamination (internal and external) and serovar predominance in fruit and stems. Of the total slicing fruit harvested from Salmonella-inoculated blossoms (ca. 6.4, 4.5, or 2.5 log10 CFU/blossom), 83.9% (47/56), 81.4% (48/59) or 71.2% (84/118) were found colonized and 67.9% (38/56), 35.6% (21/59) or 22.0% (26/118) had Salmonella internalized into the fruit, respectively. S. Poona was the most prevalent serovar isolated on or in cucumber fruits at all inoculation levels. When soil was inoculated at 1 day post-transplant (dpt), 8% (10/120) of the plants were shown to translocate Salmonella to the lower stem 7 days post-inoculation (dpi). Results identified blossoms as an important route by which Salmonella internalized at a high percentage into cucumbers, and S. Poona, the same strain isolated from the 2015 outbreak of cucumbers imported from Mexico, was shown to be well-adapted to the blossom niche.
Highlights
An increase in the incidence of foodborne disease outbreaks associated with consumption of fresh fruits and vegetables has been reported in the United States (DeWaal and Bhuiya, 2007)
Of those colonies isolated from stem segments that were positive for Salmonella (n = 135), serovars Javiana, Montevideo, Newport, and Poona each were identified at 20–30%
Many studies have been conducted to examine the possible routes for S. enterica contamination of tomatoes, melons and leafy greens, but little to no work has been done on cucumbers
Summary
An increase in the incidence of foodborne disease outbreaks associated with consumption of fresh fruits and vegetables has been reported in the United States (DeWaal and Bhuiya, 2007). While contamination of produce can occur during postharvest processing, research has shown that Salmonella has been associated with the growing environment (Islam et al, 2004a,b; Barak and Liang, 2008; Gallegos-Robles et al, 2008; Hanning et al, 2009; Patchanee et al, 2010; Gorski et al, 2011; Bell et al, 2012; Micallef et al, 2012) and plants can serve as niche environments for such enteric pathogens (Brandl et al, 2013). Salmonella has been shown to invade root tissue and translocate to the shoots (Cooley et al, 2003; Klerks et al, 2007; Barak et al, 2011) but the interaction with plants is likely Salmonella serovar (Klerks et al, 2007; Zheng et al, 2013) and plant cultivar dependent (Han and Micallef, 2014)
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