Transfer of Acanthamoeba spp. to fresh produce from water and environmental surfaces

Human noroviruses (HuNoV) are the primary cause of food-borne disease outbreaks in the United States. The most frequent commodities implicated in HuNoV outbreaks are leafy greens where contamination may occur during production and harvesting practices. With respect to the transmission of HuNoV to fresh produce, one hypothesis is that free-living amoebae that are ubiquitous in the environment (soil, sediments and water) can serve as vehicles of contamination through interaction with viruses. Here, we investigated the transfer of Acanthamoeba spp. both alone and associated with murine norovirus (MNV-1)-a surrogate for HuNoV-from water and food contact surfaces to fresh produce to understand the transfer of amoebae and the effect of virus association with amoeba on transferability, if any. In water containing a low concentration of amoebae (3 log10  cell ml(-1) ), 3·85 log10 amoebae transferred to 5 g of leafy greens, and for 5 cherry tomatoes, 3·4 to 3·5 log10 amoebae were transferred. Similarly, for high concentrations of amoeba (5 log10  cell ml(-1) ) in water, 6·14 and 5·81 log10 amoebae were transferred to 5 g leafy greens and five cherry tomatoes respectively. However, the transfer of amoebae from food contact surfaces to fresh produce was very limited. In addition, amoebae association with MNV-1 did not impact transferability.

The results of this study provide a better understanding of physical parameters (e.g. surface area and texture of fresh produce, transfer medium-water vs surface) potentially associated with transfer of free-living amoeba to fresh produce as well as the role that contaminated water (irrigation or wash water) may play in the transmission of enteric viruses associated with amoeba.