The influence of the food surface and matrix on norovirus detection by RT-qPCR

Abstract

Human noroviruses are predominant cause of epidemic and sporadic food-borne gastroenteritis in industrialized countries. Priority food categories, vehicles of viruses in many reported outbreaks, beside shellfish are food of plant origin including berries, lettuce, tomatoes and green onions. These items, as well as deli ham are often components of many ready-to-eat foods. The aim of this study was to assess the effect of different food matrices on norovirus detection. Stool sample with previously determined concentration of norovirus GII particles, was used to inoculate surface of lettuce, tomatoes, green onions and deli ham slices. For virus RNA extraction the direct method was used followed by RT-qPCR assay with SYBR green one-step kit and degenerate MON primers for the detection of GII norovirus. Obtained mean Ct values and Ct alterations calculated for each level of inoculation revealed that tomato had no inhibitory effect on NoV GII detection, followed by one log decrease of RT-PCRU due to properties of green onions, and two log decrease for lettuce and deli ham slices. The adsorption of viruses to different solid surfaces depends on their complexity and food surface factors such as presence of hydrophobic domains and acid/base groups, virus specific ligands, etc. This is important since many fruits and vegetables have complex surfaces that prevent the removal of viruses by simple washing and may decrease desiccation effects that could lead to virus inactivation.