Salmonella enterica colonization and fitness in pre-harvest cantaloupe production.

Cantaloupes have emerged as significant vehicles of widespread foodborne illness outbreaks caused by bacterial pathogens, including Salmonella. The purpose of this study was to investigate the efficiency of Salmonella colonization and internalization in cantaloupes by relevant routes of contamination. Cantaloupe plants (Cucumis melo 'reticulatus') from two cultivars 'Athena' (Eastern) and 'Primo' (Western) were grown from commercial seed. Plants were maintained in the NCSU BSL-3P phytotron greenhouse. Salmonella enterica (a cocktail of cantaloupe-associated outbreak serovars Javiana, Newport, Panama, Poona and Typhimurium) contamination was introduced via blossoms or soil at ca. 4.4 log10 CFU/blossom or 8.4 log10 CFU/root zone, respectively. Cantaloupes were analyzed for Salmonella by enrichment in accordance with modified FDA-BAM methods. Five randomly chosen colonies from each Salmonella-positive sample were typed using the Agilent 2100 bioanalyzer following multiplex PCR. Data were analyzed for prevalence of contamination and serovar predominance in fruit, stems and soil. Of the total cantaloupe fruit harvested from Salmonella-inoculated blossoms (n = 63), 89% (56/63) were externally contaminated and 73% (46/63) had Salmonella internalized into the fruit. Serovar Panama was the most commonly isolated from the surface of fruit while S. Panama and S. Poona were the most prevalent inside the fruit. When soil was inoculated with Salmonella at one day post-transplant, 13% (8/60) of the plants were shown to translocate the organism to the lower stem (ca. 4 cm) by 7 days post-inoculation (dpi). We observed Salmonella persistence in the soil up to 60 dpi with S. Newport being the predominant serovar at 10 and 20 dpi. These data demonstrate that contaminated soil and blossoms can lead to Salmonella internalization into the plant or fruit at a relatively high frequency.

Colonization and Internalization of Salmonella enterica and Its Prevalence in Cucumber Plants.

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.