The Efficacy of Chlorine and Acidified Sodium Chlorite for Disinfection of Sprout Seeds Artificially Inoculated with Salmonella as Affected by Treatment Time, Concentration, and Seed Type

Salmonella enterica has been frequently linked to major foodborne disease outbreaks. The molecular mechanisms underlying this pathogen survival on the fresh fruit surface remain largely unexplored. In this study, the environmental factors that affect the survival of Salmonella strains on the surface of selected fruits were studied. Grape tomatoes (or cantaloupe peels) were inoculated in three separate trials with 1 mL Salmonella Enteritidis ATCC13076 or Salmonella Typhimurium ATCC19585 (approximately 10 CFU/mL). After 2h air dry, samples were stored at 4°c or 25°c with 20% or 95% relative humidity for 0, 1, 3, 7, 14 days. At each time point, samples were gently washed and rigorously washed by PBS to remove loosely-attached and firmly-attached bacterial cells. Storage of grape tomatoes at 4°c resulted in significant decrease in populations of S. Enteritidis; this trend was observed at both of the tested relative humidity with the D-value as 7.25±1.05 d and 7.28±2.34 d, respectively. At different temperatures, relative humidity only had marginal effects on the bacterial survival on the surface of grape tomatoes and cantaloupes. In addition, populations of Salmonella Typhimurium ATCC19585 apparently exceeded those of Salmonella Enteritidis ATCC13076 on the surface of grape tomatoes. Furthermore, a transposon-mutagenesis library with random transposon insertion mutants of S. Enteritidis and high-throughput sequencing analysis showed that the expression of genes rcsB and nlpD were hypothesized to be associated with the survival of S. Enteritidis on grape tomatoes. In-frame deletions of the two genes in S. Enteritidis were constructed by lambda red recombinase system and respective complementation mutants were also obtained for identification of the contribution of the two genes on the bacterial survival on the surface of grape tomatoes. Thus, this study provided microbiological and molecular microbiological basis to probe the roles of putative genes in Salmonella enterica survival on the surface of fresh fruits.