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Abstract: Experimental conditions can affect the outcome of bacterial stress-tolerance assays. Growth conditions that optimize microbial recovery should be established to help evaluate the effectiveness of treatment conditions for food safety. The objectives of this study were to determine the effects of growth and recovery temperatures on pressure resistance of early stationary-phase Listeria monocytogenes in milk. The tested conditions were the following: (1) L. monocytogenes was grown at various temperatures (10, 15, 20, 25, 30, 35, 40 and 43°C), suspended in ultra-high temperature (UHT) -processed whole milk, pressure-treated at 400MPa for 2min at 21°C and recovered on Tryptic Soy Agar supplemented with 0.6% yeast extract (TSAYE) at 35°C; (2) L. monocytogenes was grown at 35 and 43°C, pressure treated in milk (400 and 500MPa, respectively, for 2min at 21°C) and recovered on TSAYE at various temperatures (4, 10, 15, 20, 25, 30, 35 and 40°C); (3) L. monocytogenes originally grown at 35°C, was pressure treated in milk (400 or 450MPa for 2min at 21°C), and recovered on TSAYE at 10°C for various time intervals (1, 2, 3, 6, 9 and 12days) then at 35°C for 5days. There was no significant difference (P >0.05) in pressure-resistance of L. monocytogenes grown at 10 to 25°C with approximately 6.5-logCFU/ml population reductions. At growth temperatures greater than 25°C, pressure resistance increased with less than 1-logCFU/ml reduction observed for L. monocytogenes originally grown at 43°C. After pressure treatment, regardless of growth temperature and pressure treatment, the greatest recovery of L. monocytogenes was within the 4 to 20°C range; maximum recovery at 10°C required approximately 24days. The time for comparable post-pressure treatment recovery could be reduced by incubation at 10°C for at least 2days followed by incubation at 35°C for 5days. The findings of the present study indicate that growth and recovery temperatures affect the pressure resistance of L. monocytogenes and should, therefore, be taken into account when assessing the adequacy of inactivation treatments. [Copyright &y& Elsevier]

Abstract: The effect of high hydrostatic pressure (HPP) and hydrodynamic pressure (HDP), in combination with chemical treatments, was evaluated for inactivation of foodborne viruses and non-pathogenic surrogates in a pork sausage product. Sausages were immersed in distilled water, 100-ppm EDTA, or 2% lactoferrin, and then inoculated with feline calicivirus (FCV), hepatitis A virus (HAV) or bacteriophage (MS2, phiX174, or T4). Each piece was packaged individually and subjected to pressure by either HDP, HPP (500 MPa, 5 min, 4 °C), or control (no pressure). On sausages immersed in water, HPP and HDP significantly (P <0.05) reduced titers of FCV by 2.89 and 2.70 log10 TCID50/ml, and HAV by log10 3.23 and 1.10, respectively, when compared to non-pressure-treated controls. Titers of T4 (1.48 and 1.10 log10 PFU/g) and MS2 (1.46 and 0.96 log10 PFU/g) were also significantly reduced by HPP and HDP treatments, respectively, in combination with water. Inoculation of viruses and bacteriophage on a meat product may have protected viruses from complete inactivation by pressure treatments. Industrial relevance: This is the first study to directly compare hydrostatic and hydrodynamic pressure technologies to inactivate microorganisms. This is also the first study to examine the inactivation of viruses and bacteriophages by pressure technology in a deli meat product. This study shows that viruses attached to meat surfaces may be protected from complete inactivation by hydrostatic and hydrodynamic pressure treatments, and these findings require more investigation into the survival of viruses in deli meat products. [Copyright &y& Elsevier]

Abstract: The objective of this study was to identify the high pressure processing conditions (pressure level, time, and temperature) needed to achieve a 5-log reduction of Vibrio parahaemolyticus in live oysters (Crassostrea virginica). Ten strains of V. parahaemolyticus were separately tested for their resistances to high pressure. The two most pressure-resistant strains were then used as a cocktail to represent baro-tolerant environmental strains. To evaluate the effect of temperature on pressure inactivation of V. parahaemolyticus, Vibrio-free oyster meats were inoculated with the cocktail of V. parahaemolyticus and incubated at room temperature (approximately 21 °C) for 24 h. Oyster meats were then blended and treated at 250 MPa for 5 min, 300 MPa for 2 min, and 350 MPa for 1 min. Pressure treatments were carried out at −2, 1, 5, 10, 20, 30, 40, and 45 °C. Temperatures ≥30 °C enhanced pressure inactivation of V. parahaemolyticus. To achieve a 5-log reduction of V. parahaemolyticus in live oysters, pressure treatment needed to be ≥350 MPa for 2 min at temperatures between 1 and 35 °C and ≥300 MPa for 2 min at 40 °C. [Copyright &y& Elsevier]

Abstract: Eimeria acervulina is a protozoan parasite that can cause intestinal lesions and reduced weight gain in chickens. E. acervulina oocysts were treated by high hydrostatic pressure and evaluated for pathogenicity, immunogenicity, and structural integrity. Pressure treatment of E. acervulina oocysts at 550 MPa for 2 min at 4, 20 or 40 °C rendered the parasites nonpathogenic to chickens. Pressure treatment at 40 °C also prevented fecal shedding of oocysts. Upon challenge with non-pressurized E. acervulina oocysts, partial immunity was observed with a reduction in lesion severity in chickens that had been inoculated with pressure-treated oocysts. No changes to the fragility and permeability of the oocyst wall or excystation of sporocysts were observed as a result of pressure treatment. Light and scanning electron microscopy revealed no changes to the whole oocyst or sporocysts. Recovery and the morphology of excysted sporozoites were altered by pressure treatment. These results suggest that pressure affects sporozoite integrity. Industrial relevance: High-hydrostatic pressure processing has been shown to inactivate various microorganisms and is utilized commercially for enhanced food safety and quality. Some pathogenic microorganisms have been inactivated by HPP yet retain immunogenic properties suggesting potential application for vaccine development. Eimeria acervulina is a poultry pathogen for which new vaccines are sought. E. acervulina is also closely related to Cyclospora cayetanensis, a foodborne human pathogen. HPP was explored for effect on E. acervulina for potential vaccine development for chickens and for insight on HPP effects on parasites for enhanced safety of human foods. [Copyright &y& Elsevier]

BAX, a polymerase chain reaction (PCR)-based pathogen detection system, was used to survey retail sprouts and mushrooms for contamination with Escherichia coli O157:H7, Salmonella, Listeria spp., and Listeria monocytogenes. No Salmonella or E. coli O157:H7 was detected in the 202 mushroom and 206 alfalfa sprout samples screened. L. monocytogenes was detected in one sprout sample, and seven additional sprout samples tested positive for the genus Listeria. BAX also detected Listeria species in 17 of the mushroom samples. Only 6 of 850 PCR assays (0.7%) failed to amplify control DNA, and therefore reagent failures and the inhibition of PCR by plant compounds were rare. The sensitivity of the detection system was evaluated by assaying samples inoculated with 10 CFU of each of the pathogens. One hundred seventy-two alfalfa sprout samples were inoculated with E. coli O157:H7, and two sets of 130 samples were experimentally contaminated with Salmonella Enteritidis and L. monocytogenes. The frequency of detection depended on the protocols used for inoculation and culturing. Inoculation of samples with approximately 10 CFU from frozen stocks yielded detection rates of 87.5 and 94.5% for L. monocytogenes and Salmonella Enteritidis, respectively, in mushrooms. The corresponding rates for alfalfa sprouts were 94.5 and 76.3%. The E. coli O157:H7 detection rate was 100% for mushrooms but only 48.6% for sprouts when standard BAX culture protocols were used. The substitution of an overnight incubation in modified E. coli medium for the 3-h brain heart infusion incubation increased the rate of E. coli O157:H7 detection to 75% for experimentally contaminated sprouts. The detection rate was 100% when E. coli O157:H7 cells from a fresh overnight culture were used for the inoculation. Test sensitivity is therefore influenced by the type of produce involved and is probably related to the growth of pathogens in the resuscitation and enrichment media. [ABSTRACT FROM AUTHOR]