Purpose: Little is known about microbial cell surface characteristics that affect adhesion on subsequent bacterial cross-contamination and transfer. This study determined the effects of surface characteristics of Salmonella on the transfer of Salmonella Newport from cucumber skin to interior flesh and peeler during peeling.
Methods: Wild type Salmonella Newport and putative attachment mutants, JDB 279 (rpoS:Tn10:lac:kan) and JDB 287 (Tn10:lac:kan insertion in the agfD/agfB intergenic region), were used to inoculate cucumbers. Bacterial transfer from cucumber skin to the flesh and peeler during peeling was quantified. The attachment strength values (SR) of Salmonella Newport to the cucumber surface were calculated using an attachment assay method. The Congo red binding assay was used to determine curli expression of Salmonella Newport.
Results: The population of curli-positive Salmonella Newport wild type attached to the cucumber surface was greater than curli-negative mutant strains (JDB 279 and JDB 287) (P<0.0001). The SR value of Salmonella Newport wild type on cucumber (0.59) was higher than that of JDB 287 (0.50) and JDB 279 (0.53), but not significantly different. Increased attachment of Salmonella Newport wild type on cucumber surface resulted in the lowest transfer to the flesh and peeler during cucumber peeling. Relatively higher bacterial transfer to the flesh (-0.84 log %, P=0.1346) and peeler (-0.60 log %, P=0.0277) was observed during peeling of cucumbers inoculated with JDB 287 compared to the transfer of Salmonella Newport wild type (-1.31 to -1.15 log %) and JDB 279 (-1.10 to -1.07 log %).
Significance: This study showed that Salmonella attachment does affect subsequent bacterial transfer during cucumber peeling. The findings will help in the development of washing and/or peeling technologies to reduce Salmonella contamination risk.