Effects of high pressure processing on Toxoplasma gondii oocysts on raspberries.

Oocysts are the environmentally resistant life stage of Toxoplasma gondii. Humans can become infected by accidentally ingesting the oocysts in water or from contaminated produce. Severe disease can occur in immunocompromised individuals, and nonimmune pregnant women can infect their offspring. Chronic infection is associated with decreased mental functions, vision and hearing problems, and some mental disorders such as schizophrenia. High pressure processing (HPP) is a commercial method used to treat food to eliminate pathogens. Treatment of produce to eliminate viable T. gondii oocysts would provide a means to protect consumers. The present study was done to better define the effects of HPP on oocysts placed on raspberries. Raspberries were chosen because they are a known source of a related human intestinal parasite, Cyclospora cayetanensis. Raspberries were inoculated with 5 x 10(4) oocysts of the VEG strain of T. gondii for 20 hr prior to HPP. Individual raspberries were exposed to 500 MPa, 400 MPa, 340 MPa, 300 MPa, 270 MPa, 250 MPa, 200 MPA, 100 MPa, or no MPa treatment for 60 sec in a commercial HPP unit (1 MPa = 10 atm = 147 psi). Treatment of raspberries with 340 MPa for 60 sec was needed to render oocysts spot inoculated on the raspberries noninfectious for mice. Treatment of raspberries with 200 MPa or less for 60 sec was not effective in rendering oocysts noninfectious for mice.

Inactivation of a norovirus by high-pressure processing.

Murine norovirus (strain MNV-1), a propagable norovirus, was evaluated for susceptibility to high-pressure processing. Experiments with virus stocks in Dulbecco's modified Eagle medium demonstrated that at room temperature (20 degrees C) the virus was inactivated over a pressure range of 350 to 450 MPa, with a 5-min, 450-MPa treatment being sufficient to inactivate 6.85 log(10) PFU of MNV-1. The inactivation of MNV-1 was enhanced when pressure was applied at an initial temperature of 5 degrees C; a 5-min pressure treatment of 350 MPa at 30 degrees C inactivated 1.15 log(10) PFU of virus, while the same treatment at 5 degrees C resulted in a reduction of 5.56 log(10) PFU. Evaluation of virus inactivation as a function of treatment times ranging from 0 to 150 s and 0 to 900 s at 5 degrees C and 20 degrees C, respectively, indicated that a decreasing rate of inactivation with time was consistent with Weibull or log-logistic inactivation kinetics. The inactivation of MNV-1 directly within oyster tissues was demonstrated; a 5-min, 400-MPa treatment at 5 degrees C was sufficient to inactivate 4.05 log(10) PFU. This work is the first demonstration that norovirus can be inactivated by high pressure and suggests good prospects for inactivation of nonpropagable human norovirus strains in foods.

Effects of high hydrostatic pressure on embryonation of Ascaris suum eggs.

High hydrostatic pressure processing (HPP) has been shown to be an effective non-thermal means of inactivating microorganisms from various food products. Little information is available regarding the effects of HPP on metazoan parasites. Outbreaks of food-borne disease have been associated with importation of food contaminated with fecal material. Ascaris suum is used as a surrogate model metazoan parasite for the human roundworm, Ascaris lumbricoides, to study the effects of treatments on the inactivation of eggs in sludge. The present study was conducted to determine the effects of HPP on A. suum eggs. Unembryonated A. suum eggs were subjected to 138-552 megapascals (MPa) for 10-60s in a commercial HPP unit. Embryonation was induced after HPP treatments by incubating eggs in 0.01N sulfuric acid at room temperature. After 21 days, 100 eggs were examined per treatment using a light microscope and the percent of embryonated eggs was determined. Embryonation was induced in 38-76% eggs that were subjected to 138 and 270MPa. No embryonation was observed in eggs exposed to pressures of 241MPa or more for 60s or in eggs exposed to 276MPa for 10-30s. These results indicate that HPP treatment could be used to protect contaminated food items by inactivating A. suum eggs and may also have potential in reducing food-borne illness resulting from fecal contamination.

Effects of high-pressure processing on Toxoplasma gondii tissue cysts in ground pork.

Ingestion of Toxoplasma gondii tissue cysts can result in severe disease in immunocompromised individuals and pregnant women. Treatment of meat and meat products to eliminate viable T. gondii tissue cysts would provide a means to protect consumers. In this study, we examined the effects of high-pressure processing (HPP) on ground pork containing viable tissue cysts of the VEG strain of T. gondii. Ground pork containing tissue cysts was exposed to 400, 300, 200, 100, or 0 MPa treatment for 30, 60, or 90 sec in a commercial HPP unit. The HPP-treated ground pork was subjected to acid-pepsin digestion and bioassayed in mice. The results of the mouse bioassay revealed that none of the mice inoculated with tissue cysts exposed to 400 or 300 MPa became infected, whereas all mice inoculated with tissue cysts exposed to 200, 100, or 0 MPa became infected with T. gondii regardless of exposure time. Results indicate that HPP treatment of ground pork with 300 MPa of pressure will render tissue cysts of T. gondii nonviable and make pork safe for human consumption.

Effects of high-pressure processing on in vitro infectivity of Encephalitozoon cuniculi.

High-pressure processing (HPP) has been shown to be an effective means of eliminating bacteria and destructive enzymes from a variety of food products. HPP extends the shelf life of products while maintaining the sensory features of food and beverages. In this study, we examined the effects of HPP on the infectivity of Encephalitozoon cuniculi spores in vitro. Spores were exposed to between 140 and 550 MPa for 1 min in a commercial HPP unit. Following treatment, the spores were loaded onto cell culture flasks or were kept for examination by transmission electron microscopy. No effect was observed on the infectivity of spores treated with 140 MPa. Spores treated with between 200 and 275 MPa showed reduction in infectivity. Following treatment of 345 MPa or more, spores were unable to infect host cells. No morphologic changes were observed in pressure-treated spores with transmission electron microscopy.