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Abstract
Salmonella is a major causal agent of outbreaks associated with low moisture foods. Salmonella is known to have several defensive mechanisms, one of which is development of biofilms, for survival in low moisture foods and environments. This study was conducted to identify genetic elements that may play critical roles in attachment and biofilm formation by Salmonella enterica serovars Tennessee and Enteritidis using mini-Tn10 transposon mutagenesis, to determine role of identified genes on attachment to peanuts and almonds, and to examine heat tolerance of wildtype and mutants in peanut butter. We found that mini tn-10 were inserted on five genes encoding bacterial cell membrane lipoprotein, DNA topoisomerase III, attachment and invasion locus protein, bacteriocin immunity protein, and cell division protein in S. Tennessee mutants which showed significantly less biofilm mass on polystyrene surface. It is found that the interrupted genes in the S. Enteritidis mutants were responsible for the biosynthesis of aldehyde dehydrogenase (EutE), cysteine desulfurase (SufS or SufE), a transporter protein, porin OmpL, and a ribbon-helix-helix protein from the CopG family. Cells of the Salmonella mutants had a significantly lower (P < 0.05) percentage of attachment than those of the wildtype parents. On average, more S. Tennessee cells attached to blanched than to unblanched peanut seeds, especially at the low inoculation level. Seed soaking time did not significantly affect the release of Salmonella cells from peanut and almond seeds to PBS. The result showed that mutants with a defective gene encoding lipoprotein or cell division protein significantly reduced the survival of the pathogen in LBNS broth and peanut butter during the heat treatments. Significantly higher reduction in the population of Salmonella was observed in regular peanut butter, followed by natural, and reduced-fat, peanut spreads. The study provides a better understanding on molecular mechanism underlying biofilm formation by Salmonella. Identified genes from this study whose products play important roles in attachment and biofilm formation and affect heat tolerance in peanut, almond seeds, and peanut butters will help to control of S. enterica in low-moisture foods and their production environments.