This study evaluated the thermal inactivation kinetic parameters of a Salmonella surrogate Enterococcus faecium (E. faecium) during feed manufacture in a university pilot feed mill setting. A batch of 227 kg mash broiler feed was pelleted after being inoculated with 1,000 mL of nalidixic acid (NaL) resistant E. faecium (5.4 log(10)CFU/g) at 70 degrees, 75 degrees, 80 degrees, and 85 degrees C for 0 to 115 s. Bacterial survival cell counts were analyzed by spread plating onto bile esculin agar plus 200 ppm of NaL. Microbial data and thermal kinetic parameters [n=6, Global-Fit and United States Department of Agriculture (USDA)-Integrated-Predictive-Modeling-Program software] were analyzed by R-software (orthogonal polynomial model). Pelleting mash broiler feed at 70 degrees, 75 degrees, 80 degrees, and 85 degrees C decreased (P < 0.05) E. faecium cell counts by 0.81, 1.18, 1.69, and 1.94 log(10) CFU/g after 115 s, respectively. D-values of orthogonal polynomial, Linear with Tail, Weibull models for E. faecium at 70 degrees, 75 degrees, 80 degrees, and 85 degrees C were 47.1 to 135.4, 42.1 to 135.2, and 51.4 to 118.8 s, respectively. These results suggest that pelleting at 80 or 85 degrees C reduces E. faecium populations the fastest, and it takes at least 50 s to reduce populations by 1 log(10) CFU/g at these temperatures. Thermal inactivation for E. faecium took longer and required higher temperatures in the feed mill than lab estimates, highlighting the importance of testing thermal inactivation temperatures in the field to ensure proper feed hygiene.

This study aims to 1) evaluate the efficacy of peroxyacetic acid (PAA) to inactivate Listeria monocytogenes in 0.1 % buffered-peptone-water; and 2) evaluate the reduction and mitigation of cross-contamination on peppers. In study-1, aliquots of 1.0-ml PAA solutions (133, 265, and 448 ppm) were added to the first 6 wells of 8-strip-deep well microplates. Then, 0.1 ml of serially diluted nalidixic-acid-resistant (NaL) L. monocytogenes was added and mixed immediately with a multichannel pipette. After exposure for 0, 5, 15, 30, and up to 120-s, 1 ml of 2 × D/E neutralized solution was added to terminate the reaction followed by spread-plating onto tryptic soy agar +200 ppm NaL and incubated at 35 °C for 48 h. In study-2, 5 inoculated red peppers were triple-washed with 15 uninoculated green peppers with 0, 23, 53, and 96 ppm of PAA and analyzed using MPN-method. L. monocytogenes counts were <0.3 log10 CFU/ml after exposure to 133, 265, and 448 ppm of PAA for 120, 90 and 60 s, respectively and fit the Linear and Weibull Models. Applying 23–96 ppm of PAA reduced L. monocytogenes by 2.03–3.32 log10MPN/g and transferred cross-contaminated cell counts by 2.36–3.17 log10MPN/g, with no differences (P > 0.05) compared to the water only treatment. Results suggested that applying allowable concentrations (23–96 ppm) of PAA during triple-wash does not show promising anti-Listeria activity on peppers. Future studies are needed to determine the minimum concentrations of the PAA solution required to effectively reduce and mitigate microbial cross-contamination of Listeria monocytogenes on peppers.

This study evaluated the effectiveness of triplewashing with a hydrogen peroxide (H2O2)-peroxyacetic acid (PAA) mixer to mitigate microbial cross-contamination of Salmonella Typhimurium and the surrogate bacteria Enterococcus faecium on butternut squash. To produce cross-contamination, one or two butternut squash were dip-inoculated with nalidixic acid-resistant S. Typhimurium (4.03 log10MPN/g) or E. faecium (4.20 log10MPN/g) and then mixed with 6 ("1:6") or 5 ("2:5") uninoculated fresh clean squash followed by triplewashing for 45 s in water, water, and then the H2O2-PAA mixer at doses 0, 0.0064, 0.25, 0.50, and 0.84 ml/dL. The most-probable -number was used to determine microbial population. Triple-washing squash with 0.25-0.84 ml/dL H2O2-PAA mixer resulted in greater (P < 0.05) reductions of S. Typhimurium and E. faecium by 2.50-3.10 and 2.01 to 3.43 log10MPN/g, respectively, than the 0 and 0.0064 ml/dL treated samples. Applying 0.25-0.84 ml/dL H2O2-PAA mixer resulted 1.02 to 1.31 and 0.84 to 1.12 log10MPN/g cross-contaminated S. Typhimurium cell counts in the "1:6" and "2:5" ratio tests, respectively. E. faecium showed similar reduced cell counts and cross-contaminated cell counts in most tested treatments compared to S. Typhimurium, indicating it is an appropriate surrogate bacterium for Salmonella during post-harvest produce washing challenge studies.

This study aims to determine the minimal concentrations of a 23% hydrogen peroxide and 5.3% peroxyacetic acid (H2O2-PAA) mixture required to prevent microbial cross-contamination of Salmonella and the potential surrogate Enterococcus faecium on tomatoes. Nalidixic acid-resistant (NaL) S. Typhimurium (5.15 log10MPN/g) or E. faecium (5.29 log10MPN/g) inoculated tomatoes were triple-washed for 45 s at each step using a water + antimicrobial + water (WAW) or water + water + antimicrobial (WWA) wash strategy with a solution of H2O2-PAA at 0 (control) and off-label concentrations of 0.50 and 0.70%. A most probable number (MPN) method was used to analyze the microbial reductions and cross-contamination trasnferred cell counts. Significant reductions (P < 0.05) of Salmonella were only achieved when the off-label concentration of 0.7% H2O2-PAA was applied using the WWA strategy. When LS-Means were calculated, there were no significant differences (P > 0.05) in reductions of S. Typhimurium or E. faecium regardless of wash strategy. Cross-contamination of S. Typhimurium was prevented at 0.7% of H2O2-PAA using the WWA strategy, and E. faecium was prevented at and above 0.50% of H2O2-PAA, respectively, regardless of wash strategy. There were no differences (P > 0.05) of bacterial cell survival in triple-wash solutions between S. Typhimurium and E. faecium. Results suggested that E. faecium could be an acceptable surrogate for S. Typhimurium when validating antimicrobial washing systems on tomatoes. The off-label concentrations of H2O2-PAA that were tested resulted in non-detectable microbial cross-contamination. Off-label use of antimicrobials is not encouraged until future research determines the safety of these greater concentrations prior to their implementation in commercial settings.

The efficacy of a triple-wash system to reduce and mitigate cross-contamination of Salmonella Typhimurium and Enterococcus faecium was tested on tomatoes. Tomatoes were dip-inoculated with S. Typhimurium or E. faecium followed by triple-washing for 45 s at each wash step: water + antimicrobial + water (WAW) or water + water + antimicrobial (WWA). A mixture [23 ml/dL hydrogen peroxide + 5.3 ml/dL peroxyacetic acid (SaniDate-5.0, SD)] was tested at 0, 0.0064, 0.1, and 0.25 ml/dL. Microbial population was estimated using a modified most-probable-number (MPN) method. Reductions of S. Typhimurium were similar (P > 0.05) to E. faecium (1.83–3.53 vs 1.72–3.65 log10MPN/g) with the greatest reductions at 0.25 ml/dL of SD. No differences (P > 0.05) were seen in reductions of S. Typhimurium or E. faecium regardless of wash strategy. Application of 0.25 ml/dL of SD in WAW or WWA wash strategy resulted in the lowest (P < 0.05) cell counts than the lower concentration treatments for S. Typhimurium (0.16–0.69 log10MPN/g) and E. faecium (−0.41 log10MPN/g). There were no differences (P > 0.05) in of survival between S. Typhimurium and E. faecium after treatment with the triple-wash strategies. Results suggest that E. faecium could be an acceptable surrogate for S. Typhimurium when validating antimicrobial washing systems on tomatoes.

This study compares kinetic parameters of Salmonella and surrogate Enterococcus faecium in mash broiler feed during thermal inactivation. Two-gram samples of mash broiler feed were added into a filtered sample bag and inoculated with nalidixic acid (NaL, 200 ppm) resistant S. Typhimurium or Enterococcus faecium, followed by vacuum-packaging and heating in a circulated thermal water bath at 75°, 85°, and 95°C for 0 to 180 s. Counts of bacterial survival were analyzed on tryptic soy agar and bile esculin agar plus 200 ppm of NaL. Microbial data and thermal kinetic parameters (n = 8, Global-Fit and United States Department of Agriculture [USDA]-Integrated-Predictive-Modeling-Program software) were analyzed by JMP software. Heating mash broiler feed at 75°, 85°, and 95°C decreased (P < 0.05) Salmonella cell counts by >6 log10CFU/g after 180, 60, and 50 s, respectively. Heating E. faecium in feed at 75°, 85°, and 95°C for 180, 120, and 70 s achieved reductions of 3, 6, and >6.5 log10CFU/g, respectively. D-values of linear, Weibull models, and z-value of Salmonella at 75°, 85°, and 95°C were 1.8 to 11.2, 4.2 to 21.8, and 28.6 s, respectively, which were lower (P < 0.05) than those of E. faecium (3.7–18.1, 8.5–34.4, and 34.1 s). Linear with Tail, Linear with Tail and Shoulder, and Weibull with tail equations revealed that E. faecium were more resistant (P < 0.05) to heat than Salmonella as shown by longer “Shoulder-time” (26.5 vs. 16.2 s) and greater “Tail” effect (4.4–4.5 vs. 2.5–2.6 log10CFU/g). Results clearly suggested that E. faecium can be used as a surrogate for Salmonella to validate thermal inactivation during feed manufacture.