Root internalization, transport and in-planta survival of Salmonella enterica serovar Newport in sweet basil

It is now acknowledged that food-borne pathogens present in the irrigation water or soil can become associated with crop plants in the field, penetrate internal plant tissues via the root, translocate and survive inside plants. Only little information is available concerning interaction between enteric pathogens and plants. The present study evaluated the potential for contamination of the aromatic plant, sweet basil during cultivation, by Salmonella enterica serovar Newport. Root internalization was plant-age-dependent, with the highest susceptibility occurring at the beginning of the rapid growth phase of the root. Higher incidence of internalization was detected in vegetative than reproductive plant organs, pointing at bacterial transport in the transpiration stream. Internalized Salmonella survived only <30h in the phyllosphere. In contrast, survival of Salmonella on the leaf surface was much pronounced (at least 8 days), and the initial decay rate was lower at the abaxial (lower) compared with the adaxial (upper) side of the leaf. Although the experiments were conducted with high concentration of Salmonella unlikely to happen in the field, internalization occurred at a low frequency and in-planta survival was limited to less than 30h. These findings imply that leaf surface contamination, rather than root internalization, may pose higher risk for human infection following consumption of contaminated basil.