Purpose: To compare survival of foodborne pathogens on wet- and dry-inoculated cilantro plants in the field and in an environmental growth chamber.
Methods: Mature cilantro plants were inoculated with rifampicin-resistant attenuated strains of Escherichia coli O157:H7 ATCC 700728 (commercial field Salinas, California and laboratory growth chamber) and Salmonella Typhimurium (laboratory only). Bacteria were applied to the plants (4 to 8 log CFU/g) via spraying an aqueous solution or dusting freeze-dried bacterial powders mixed with chalk. Survival for up to 10 h in the field or 48 h in the laboratory (23 °C, 30% and 80% RH) was compared. To recover inoculated bacteria, plants were added to 0.1% peptone and stomached, and then samples were plated onto TSA or filtered onto CHROMagar O157 or CHROMagar Salmonella, all containing rifampicin.
Results: In the field, E. coli O157:H7 populations declined by 3 log after 10 h on cilantro plants inoculated by either method. These declines were similar to those observed a growth chamber set to 30% RH (2 and 3 log reduction after 6 h for wet and dry inoculation, respectively). Salmonella populations changed by < 1 log for wet and dry inoculation methods under the same conditions. In contrast, at 80% RH, E. coli O157:H7 and Salmonella populations on cilantro were consistent over 48 h when inoculated via either wet or dry methods.
Significance: Inoculation method did not affect survival of E. coli O157:H7 or Salmonella on cilantro plants. Low RH better mimics survival of foodborne pathogens under field conditions in Salinas, CA.