Purpose: This study examined the preharvest risks of cucumber when exposed to Salmonella spp. on blossoms and in soil.
Methods: Cucumber plants (Cucumis sativus var. sativus) from two cultivars, Puccini (pickle) and Thunder (slicer), were grown from commercial seed. Plants were maintained in the NCSU BSL-3 phytotron greenhouse. Salmonella (a cocktail of serovars Javiana, Montevideo, Newport, Poona, and Typhimurium) contamination was introduced via blossoms or soil at six log CFU/blossom or eight log CFU/root zone. Cucumbers were analyzed for Salmonella spp. by enrichment in accordance with modified FDA-BAM methods. Five randomly chosen colonies from each Salmonella spp.-positive sample were serotyped using the Agilent 2100 bioanalyzer following multiplex PCR. Data were analyzed for prevalence of contamination, serovar predominance in fruit and stems, and differences between cucumber cultivars.
Results: Of the cucumber fruit harvested from Salmonella serovar-inoculated blossoms (n=58), 83% (48 of 58) were contaminated and 67% (39 of 58) had Salmonella spp. internalized into the fruit; of those positive for Salmonella spp., greater than 70% (15 of 210) were identified as Salmonella Poona. Prevalence of contamination was equivalent when comparing cultivars (pickle vs. slicer) and location of contamination (outer vs. inner). When soil was inoculated at the base of 20 day-old plants, only 8% (10 of 120) of the plants were shown to translocate Salmonella spp. to the lower stem after seven dpi; of those positive, serovars Javiana, Montevideo, Newport and Poona each were identified at 20 to 30% (n=132).
Significance: These results identified blossoms as a route by which Salmonella spp. are internalized at a high percentage into cucumbers. Salmonella Poona, the same strain isolated from the 2015 outbreak of cucumbers imported from Mexico, was shown adapted to the blossom niche.