Abstract
Fresh produce has been identified as an important vehicle for foodborne pathogen transmission and fresh culinary herbs have occasionally been associated with human pathogens and illness. In this study, the fate of human NoV surrogates [murine norovirus 1 (MNV-1) and Tulane virus (TV)] and three strains of Salmonella enterica on pre-harvest basil (Ocimum basilicum) was investigated. The persistence after contamination via either leaf surface or plant substrate was tested respectively. After 3 days, both MNV-1 and TV on pre-harvest leaves were at non-detectable levels (>5.5-log reduction for MNV-1 and >3.3-log reduction for TV). The three Salmonella strains showed consistent reductions of 3- to 4-log. At day 6 and 9, all the tested samples showed low levels of infectivity which were close or below the detection limits (1.7-log PFU/sample leaf for MNV-1 and TV, 0.7-log CFU/sample leaf for Salmonella) except for S. Thompson FMFP 899, one out of three samples showed to maintain present at exceptional high levels (day 6: 5.5-log CFU/sample leaf; day 9: 6.7-log CFU/sample leaf). Possibilities of microbial internalization into the edible parts of basil via the roots was demonstrated with both MNV-1 and S. enterica Thompson FMFP 899. The infectivity of internalized MNV-1 and S. enterica both decreased to non-detectable levels within 9 days after inoculation. Moreover, it should be noticed that very high microbial inoculation was used in the experimental set-up (8.46-log PFU/ml of MNV-1, 8.60-log CFU/ml of S. enterica), which is abnormal in the real-life expected contamination scenario. Within the tested scenarios in this study, S. enterica contaminated on the adaxial leaf surface of basil plants while in growth, and remained/reached a high population of over 6-log CFU/sample leaf after 9 days in one out of three samples, thus showed the highest potential for causing foodborne infection.
Highlights
Fresh produce has been identified as an important vehicle for the transmission of foodborne pathogens including Salmonella, Shiga toxin-producing E. coli (STEC), Listeria monocytogenes, human noroviruses (NoVs), Hepatitis A virus, etc. (Li et al, 2015; Alegbeleye et al, 2018)
Three days post inoculation on the adaxial leaf surfaces of the 4 week old pre-harvest basil plants, both MNV-1 and Tulane virus (TV) were at non-detectable levels, corresponding to >5.5-log reductions for MNV-1 (Figure 1A) and > 3.3-log reductions for TV (Figure 1B) of the initial inoculum levels
Both NoVs and Salmonella are leading foodborne pathogens worldwide which can be transmitted by fresh produce
Summary
Fresh produce has been identified as an important vehicle for the transmission of foodborne pathogens including Salmonella, Shiga toxin-producing E. coli (STEC), Listeria monocytogenes, human noroviruses (NoVs), Hepatitis A virus, etc. (Li et al, 2015; Alegbeleye et al, 2018). Fresh produce has been identified as an important vehicle for the transmission of foodborne pathogens including Salmonella, Shiga toxin-producing E. coli (STEC), Listeria monocytogenes, human noroviruses (NoVs), Hepatitis A virus, etc. Fresh culinary herbs have occasionally been associated with human pathogens and illness (FDA, 2013). It is of interest to investigate the fate of foodborne pathogens once they contaminate culinary herbal plants, both via leaves and roots, in order to provide data for comprehensive risk assessments. The fate of human NoV surrogates [murine norovirus 1 (MNV-1) and Tulane virus (TV)] and three strains of Salmonella enterica on pre-harvest basil leaf surfaces were investigated. The internalization of the MNV1 and Salmonella into edible parts of basil from the roots was evaluated
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