Inactivation susceptibility of enteric viruses treated with iron, plant, and bacterial constituents

Date
2018
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
Human norovirus (HuNov) is the leading global cause of acute gastroenteritis. An estimated 20 million cases of norovirus illness occur annually in the United States, of which more than 56,000 require hospitalization and up to 800 result in death. Norovirus is transmitted via the fecal-oral route through direct contact with an infected individual, consumption of contaminated food or water, and contact with contaminated surfaces. The number of domestically-acquired norovirus illnesses in the United States attributed to foodborne transmission is estimated at 5.5 million. Foods that require considerable handling and which do not receive treatment to inactivate virus prior to consumption are particularly vulnerable to serve as norovirus transmission vehicles. ☐ Human norovirus prevalence is likely due in part to its ability to adhere to, persist on, and transfer among a variety of food and food contact surfaces. Norovirus directly interacts with cell surface glycans of host cells as well as similar molecules found on some plant tissues and fecal bacteria. The impact of these interactions for norovirus transmission and persistence has not been fully elucidated. Methods to remove or inactivate norovirus from fresh produce without comprising sensory attributes have limited efficacy. Strategies to mitigate contamination are needed to enhance the safety of foods. ☐ In the absence of an efficient cell-culture model for HuNov, research was undertaken to evaluate the resistance of HuNov surrogates, Tulane virus (TV) and murine norovirus (MNV), to inactivation strategies and ecological pressures. Novel viral inactivation strategies evaluated included zero-valent iron (ZVI) and plant-derived proteases for potential to enhance safety of water and ready-to-eat produce, respectively. Viral and bacterial interactions were evaluated for direct association, antiviral bacterial metabolic products, and bacterial impact on viral thermal and chlorine resistance. ☐ Inactivation strategies demonstrated effectiveness of ZVI treatment to remove virus from water, but limited efficacy of plant-derived proteases to reduce infectivity of virus. ZVI removed approximately 2 to 4 log10 of TV and MNV, respectively, from water filtered through sand columns with ZVI incorporated. Buffers of various pH and osmolality did not enhance elution of virus as compared to elution by water from ZVI suggesting virus irreversibly associates with ZVI or is inactivated. Bromelain treatment (2500 ppm) of MNV for 10 minutes at 50°C resulted in a 2.5-log10 reduction in infectivity; whereas, infectivity of TV was not reduced by plant-derived protease treatments. ☐ Recovery of TV suspended in enteric, skin, soil, and phyllospheric bacteria was not impeded as compared to TV alone suggesting a lack of direct, stable binding between virus and bacteria. Exposure of human norovirus to the metabolic growth products (cell-free supernatant, CFS) of Bifidobacterium bifidum, a bacterium previously reported to constitutively produce extracellular glycosidases that degrade histoblood group antigens (HBGA), did not enhance viral recovery from stool or in coculture with Enterobacter cloacae as compared to phosphate buffered saline. TV propagation in cell culture was not impeded by the addition of CFS of B. bifidum. Exposure of MNV and TV to the CFS of Bacillus subtilis 168 and Enterococcus faecalis 19433 resulted in 2-log10 PFU/ml and less than one-log10 PFU/ml reductions in propagation, respectively, relative to viral propagation in media alone. Exposure of MNV and TV to the CFS of ten other bacterial species associated with the human intestinal tract, human skin, soil, or phyllosphere did not decrease viral propagation. ☐ Suspension of TV in commercially-prepared bacterial peptidoglycan (PEP) of Bacillus subtilis increased viral thermal and chlorine inactivation resistance. TV was undetectable (>3.7-log10 PFU/ml reduction) after 60°C treatment when suspended in PBS and LPS, but was reduced by only 1.99 log10 PFU/ml in PEP. Chlorine treatment of 200 ppm rendered TV undetectable (>3-log10 PFU/ml reduction) in PBS and LPS; however, TV was still detected in PEP, reduced by 2.86 log10 PFU/ml. Suspension of TV in commercially-prepared lipopolysaccharide of Escherichia coli O111:B4 did not significantly affect viral resistance to the chlorine and thermal inactivation treatments tested. ☐ Collectively, these data indicate ZVI has potential for remediation of viral-contaminated water, but plant-derived proteases were not antiviral at commercially-relevant conditions. Bacterial metabolic products had limited antiviral properties under the conditions tested, and the presence of bacteria may require more stringent treatment conditions to inactivate virus. These data are significant for understanding factors important for norovirus transmission and resistance and for identifying strategies to reduce norovirus contamination risk, thereby enhancing the safety of food and water. ☐ INDEX WORDS: Norovirus, Zero-valent iron, Plant protease, Bacteria binding, Inactivation
Description
Keywords
Biological sciences, Bacteria binding, Inactivation, Norovirus, Plant protease, Zero-valent iron
Citation