Purpose: The objective of this research was to assess and characterize the possible routes of Salmonella internalization into peanut seedpods and plant tissues.
Methods: The internalization of Salmonella Typhimurium was studied by exposing peanut seedpods to cell suspensions and inoculated soil containing 7.0 log CFU/g at different temperatures and variable times (n = 3 - 6). For sterile soil experiments, moisture level and soil type were studied. Internalized cells were determined by swabbing and rinsing the interior surfaces of the seedpod. External and internalized cells were quantified using differential tryptic soy agar. Peanut plants were also grown in inoculated soil and the presence of Salmonella in the roots, stems, and leaves was determined.
Results: Using cell suspensions, the average count of internalized cells after 22-h exposure ranged from 3.4 log CFU/pod at 16°C to 6.4 log CFU/pod at 37°C which resulted in rates of internalization of 0.07 and 13.7%, respectively. This trend was consistent with 4-h exposure results. Pods exposed to Salmonella-inoculated soils at < 10% moisture content had no detectable (< 10 CFU/pod) internalized cells, but when water content was > 15% the mean internal count was 4.2 log CFU/pod. Plants that were seeded in inoculated soils had detectable levels of Salmonella inside of roots and stems.
Significance: The direct uptake of Salmonella by peanut seedpods indicated a potential route for product contamination is influenced by moisture and temperature. This work suggests that peanut seedpods and whole plants are susceptible to Salmonella infiltration, which indicates an entry point into a peanut processing facility from the growing field.