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The exceptional stability of enteric viruses probably resides in their capsids. The capsid functions of inactivated human picornaviruses and feline calicivirus (FCV) were determined. Viruses were inactivated by UV, hypochlorite, high temperature (72°C), and physiological temperature (37°C), all of which are pertinent to transmission via food and water. Poliovirus (PV) and hepatitis A virus (HAV) are transmissible via water and food, and FCV is the best available surrogate for the Norwalk-like viruses, which are leading causes of food-borne and waterborne disease in the United States. The capsids of all 37°C-inactivated viruses still protected the viral RNA against RNase, even in the presence of proteinase K, which contrasted with findings with viruses inactivated at 72°C. The loss of ability of the virus to attach to homologous cell receptors was universal, regardless of virus type and inactivation method, except for UV-inactivated HAV, and so virus inactivation was almost always accompanied by the loss of virus attachment. Inactivated HAV and FCV were captured by homologous antibodies. However, inactivated PV type 1 (PV-1) was not captured by homologous antibody and 37°C-inactivated PV-1 was only partially captured. The epitopes on the capsids of HAV and FCV are evidently discrete from the receptor attachment sites, unlike those of PV-1. These findings indicate that the primary target of UV, hypochlorite, and 72°C inactivation is the capsid and that the target of thermal inactivation (37°C versus 72°C) is temperature dependent.

At 2 degrees and 30 degrees C, enteroviruses are more stable on the acid than on the alkaline side of neutrality. In the range from pH 3 to 9, temperature is so influential that the fastest inactivation rate at 2 degrees C is slower than the slowest inactivation rate at 30 degrees C. Specific ions or salts also affect the rate of inactivation of enteroviruses. NaCl and other chloride salts enhance the inactivation of poliovirus at pH 3. NaCl is considerably less effective against poliovirus in the range of pH 4.5 to 7.0 than at pH less than 4.5. Loss of RNA infectivity of the virus particle proceeds as rapidly as the loss of infectivity of the particle itself, except at pH 3 in the presence of MgCl2. Inactivation results in alterations to the physical integrity of enteroviruses. At pH 5 and 7, RNA hydrolysis of poliovirus particles occurs; and at pH3, 5,6, and 7 the nucleic acid becomes susceptible to ribonuclease. Only virus particles inactivated at pH 3 show a sensitivity to chymotrypsin. The hemagglutinins of echovirus type 7 are destroyed during inactivation at pH 3,4,5, and 6; but at pH 6 this alteration precedes the loss of infectivity. The pH of the suspension is a primary determinant of the mechanism of virus destruction and possibly of the loss of infectivity at these temperatures.

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The microbiology of Plastic and wooden cutting boards was studied, regarding cross-contamination of foods in home kitchens. New and used Plastic (four polymers plus hard rubber) and wood (nine hardwoods) cutting boards were cut into 5-cm squares (“blocks”). Escherichia coli (two nonpathogenic strains plus type O157:H7), Listeria innocua, L. monocytogenes, or Salmonella typhimurium was applied to the 25-cm2 block surface in nutrient broth or chicken juice and recovered by soaking the surface in nutrient broth or pressing the block onto nutrient agar, within 3–10 min or up to ca. 12 h later. Bacteria inoculated onto Plastic blocks were readily recovered for minutes to hours and would multiply if held overnight. Recoveries from wooden blocks were generally less than those from plastic blocks, regardless of new or used status; differences increased with holding time. Clean wood blocks usually absorbed the inoculum completely within 3–10 min. If these fluids contained 103–104 CFU of bacteria likely to come from raw meat or poultry, the bacteria generally could not be recovered after entering the wood. If ≥106 CFU were applied, bacteria might be recovered from wood after 12 h at room temperature and high humidity, but numbers were reduced by at least 98%, and often more than 99.9%. Mineral oil treatment of the wood surface had little effect on the microbiological findings. These results do not support the often-heard assertion that Plastic cutting boards are more sanitary than wood.

During inactivation of poliovirus type 1 (PV-1) by exposure to UV, hypochlorite, and heat (72°C), the infectivity of the virus was compared with that of its RNA. DEAE-dextran (1-mg/ml concentration in Dulbecco's modified Eagle medium buffered with 0.05 M Tris, pH 7.4) was used to facilitate transfecting PV-1 RNA into FRhK-4 host cells. After interaction of PV-1 RNA with cell monolayer at room temperature (21 to 22°C) for 20 min, the monolayers were washed with 5 ml of Hanks balanced salt solution. The remainder of the procedure was the same as that for the conventional plaque technique, which was also used for quantifying the PV-1 whole-particle infectivity. Plaque formation by extracted RNA was approximately 100,000-fold less efficient than that by whole virions. The slopes of best-fit regression lines of inactivation curves for virion infectivity and RNA infectivity were compared to determine the target of inactivation. For UV and hypochlorite inactivation the slopes of inactivation curves of virion infectivity and RNA infectivity were not statistically different. However, the difference of slopes of inactivation curves of virion infectivity and RNA infectivity was statistically significant for thermal inactivation. The results of these experiments indicate that viral RNA is a primary target of UV and hypochlorite inactivations but that the sole target of thermal inactivation is the viral capsid.Leading causes of food-borne, and probably water-borne, disease in the United States are the Norwalk-like viruses (NLVs) of the family Caliciviridae and the hepatitis A virus (HAV) of the family Picornaviridae (11). Poliovirus (PV) is the type species of the genus Enterovirus in the Picornaviridae family (19). PV has the same genomic structure and gene organization as that of HAV and has a close phylogenetic relationship with the NLVs (26). We have studied the inactivation of PV, HAV, and feline calicivirus (FCV, which is often used as a surrogate for NLVs because NLVs have no laboratory host cell line). Inactivating agents used in these studies were UV, hypochlorite, and heat (72°C), all of which are commonly used in food processing or preparation and in water disinfection.These simple viruses comprise only a single strand of RNA coated with protein. The RNA contains the genetic information by which intracellular infection results in production of progeny virus, so infectivity ultimately resides in the RNA. The coat protein (capsid) performs three functions: (i) protection of the RNA against environmental degradation and in transit down the digestive tract until susceptible cells are reached; (ii) attachment to the receptor of a susceptible cell, whereby the viral particle is engulfed and the capsid removed, to initiate the infection; and (iii) antigenic activity that evokes an immune response by the host and reacts with the antibody that has been produced. We have shown that capsids of HAV, vaccine PV type 1 (PV-1), and FCV inactivated (from an initial titer of ϳ1,000 PFU/ml) by UV, hypochlorite, or high temperature ...