SARS-CoV-2 surrogate bacteriophage φ6 cross-contamination between fruits and gloves, survival on discarded gloves and inactivation by photodynamic treatment.

This study assessed the SARS-CoV-2 surrogate bacteriophage φ6 cross-contamination between high-density polyethylene or polyvinyl chloride gloves and fruits (tomato and cucumber) using different inoculum levels (6.0 and 4.0 log PFU/sample). Bacteriophage φ6 survival on contaminated gloves was assessed over 9 days at 25 °C. The effectiveness of photodynamic treatment using curcumin as a photosensitizer to inactivate φ6 on fruits was determined. The fruit type and the glove material influenced the φ6 transfer. Longer contact times resulted in greater φ6 transfer. The highest φ6 transfer occurred from tomato to HDPE glove (0.8% or -1.1 log % transfer) after 30 s of contact at the higher inoculum level. Bacteriophage φ6 was detected on cross-contaminated HDPE gloves for up to 6 days. Bacteriophage φ6 survived better on vinyl gloves cross-contaminated by cucumber vs. tomato (detected up to 6 vs 3 days). Photodynamic inactivation of φ6 was time-dependent and varied with the tested fruit but was not influenced by viral starting concentration. Photodynamic treatment decreased the φ6 titer by 3.0 and 2.2 log PFU/sample in tomato and cucumber, respectively. Transmission electronic microscopy showed that photodynamic treatment changed the structure of the φ6 capsid. These findings may help in the management of SARS-CoV-2 contamination risks in fruit handling. They may also help in the establishment of effective measures to manage cross-contamination risk.

Models for the Inactivation of Foodborne Pathogens in Salad Dressing from Challenge Studies.

The Association for Dressings and Sauces' (ADS) members have conducted challenge studies on salad dressing products to assess pathogen survival. Data from 79 different challenge studies provided by ADS were used in this analysis. The acid-moisture ratio, pH, incubation temperature, and ingredient details were provided for each study. Linear regression models were used to predict the time to 3-log, 4-log, and 5-log reduction as a function of study parameters. A statistically based approach also was used to estimate the concentration of pathogens in ingredients based on testing history. This was combined with decline modeling to estimate pathogen concentration over time. The time-to-five log reduction for each of the target pathogens were highly skewed. A logarithmic transformation of time to 5 log reduction resulted in approximately normal distributions. Incubation temperature and formulation pH were highly significant (p < 1E-6), in predicting the number of days to a five-log reduction of Escherichia coli O157:H7, while the percentage of spices in the formulation is also quite significant (p = 0.01). Salmonella modeling showed that the most highly significant parameter was the percentage of water (p < 1E-8). Other parameters in order of descending significance include the percent fruit (p = 0.00032), incubation temperature (p = 0.00268), followed by percent sugar (p = 0.02161) and percent vegetables (p = 0.03149). The most significant parameter in predicting Listeria monocytogenes reduction was incubation temperature (p = 0.000687), followed by acid moisture ratio (p = 0.012423). The next two significant parameters in the Listeria model were percent lipid (p = 0.023772) and percent water (p = 0.025701). The least significant parameter that meets the minimum criteria for inclusion in the Listeria model (p < 0.05) was percent fruit (p = 0.047074). Our analysis will be useful in developing risk-based approaches to continue to assure the safety of commercially prepared salad dressings.

Cooling Uncovered Foods at a Depth of ∼5.1 cm (2 in.) or Less Poses Little Risk of Pathogen Growth.

The U.S. Food and Drug Administration has guidelines for cooling cooked foods in retail operations. Data on foodborne illness risk factors in restaurants indicate that cooling is often out of compliance with these guidelines. We sought to identify factors under the control of the operator that had a significant effect on the cooling rates of cooked foods. Minneapolis Minnesota Health Inspectors were trained in standardized operating procedures for cooling data collection. Data loggers set to appropriate time intervals and calibrated to ±0.5 °C (∼1°F) were used in data collection. Analysis was performed using the R statistical computing language version 4.2.2. Preexisting pathogen models were used to predict Log CFU increases of Clostridium perfringens or Bacillus cereus. Data from 224 recipes were recorded by inspectors between October 2018 and October 2019. Food depth had a highly significant effect (p = 8.90E-08) on cooling rate. The use of an ice bath or ice wand was also significant (p < 0.005). There was a significant correlation between container material (metal or plastic) and food depth because foods with a greater depth are often being cooled in plastic containers. Foods at a depth greater than 5.1 cm (2 in.) that cooled faster than 0.23 log(°C)/h were often wholly or partially cooled in blast chillers or freezers, cooled using an ice bath or ice wand (or both), or were composed of protein pieces (e.g., chicken wings) that facilitated more rapid cooling due to air gaps in the food. Foods in shallow containers at a food depth of less than or equal to ∼5.1 cm (2 in.) that cooled more slowly than 0.23 log(°C)/h were being cooled at temperatures greater than 5 °C (41°F) or were partially or wholly covered. These foods also showed little evidence of pathogen growth from predictive models. Our analysis shows that cooling foods in shallow containers at a food depth of less than or equal to ∼5.1 cm (2 in.) poses little risk of significant pathogen growth.

Predicting the impact of temperature and relative humidity on Salmonella growth and survival in sliced chard, broccoli and red cabbage.

This study assessed the fate of a Salmonella enterica cocktail (S. Typhimurium, S. Enteritidis, S. Newport, S. Agona and S. Anatum; initial counts 3.5 log CFU/g) in minimally processed sliced chard, broccoli and red cabbage at 16 conditions of different temperature (7, 14, 21 and 37 °C) and relative humidity (RH; 15, 35, 65 and 95%) over six days (144 h). Linear regression was used to estimate the rate change of Salmonella in cut vegetables as a function of temperature and relative humidity (RH). R2 value of 0.85, 0.87, and 0.78 were observed for the rates of change in chard, broccoli, and red cabbage, respectively. The interaction between temperature and RH was significant in all sliced vegetables. Higher temperatures and RH values favored Salmonella growth. As temperature or RH decreased, the rate of S. enterica change varied by vegetable. The models developed here can improve risk management of Salmonella in fresh cut vegetables.

Ozone and photodynamic inactivation of norovirus surrogate bacteriophage MS2 in fresh Brazilian berries and surfaces.

This study assessed the efficacy of ozone (bubble diffusion in water; 6.25 ppm) and photodynamic inactivation (PDT) using curcumin (75 µM) as photosensitizer (LED emission 430-470 nm; 33.6 mW/cm2 irradiance; 16.1, 20.2, and 24.2 J/cm2 light dose) against the Norovirus surrogate bacteriophage MS2 in Brazilian berries (black mulberry and pitanga) and surfaces (glass and stainless steel). Contaminated berries and surfaces were immersed in ozonized water or exposed to PDT-curcumin for different time intervals. Transmission electron microscopy was used to assess the effects of the treatments on MS2 viral particles. The MS2 inactivation by ozone and PDT-curcumin varied with the fruit and the surface tested. Ozone reduced the MS2 titer up to 3.6 log PFU/g in black mulberry and 4.1 log PFU/g in pitanga. On surfaces, the MS2 reduction by ozone reached 3.6 and 4.8 log PFU/cm2 on glass and stainless steel, respectively. PDT-curcumin reduced the MS2 3.2 and 4.8 log PFU/g in black mulberry and pitanga and 2.7 and 3.3 log PFU/cm2 on glass and stainless steel, respectively. MS2 particles were disintegrated by exposure of MS2 to ozone and PDT-curcumin on pitanga. Results can contribute to establishing effective practices for controlling NoV in fruits and surfaces, estimated based on MS2 bacteriophage behavior.

Efficacy of Peracetic Acid and Chlorine on the Reduction of Shiga Toxin-producing Escherichia coli and a Nonpathogenic E. coli Strain in Preharvest Agricultural Water.

Produce-borne outbreaks of Shiga toxin-producing Escherichia coli (STEC) linked to preharvest water emphasize the need for efficacious water treatment options. This study quantified reductions of STEC and generic E. coli in preharvest agricultural water using commercially available sanitizers. Water was collected from two sources in Virginia (pond, river) and inoculated with either a seven-strain STEC panel or environmental generic E. coli strain TVS 353 (∼9 log10 CFU/100 mL). Triplicate inoculated water samples were equilibrated to 12 or 32°C and treated with peracetic acid (PAA) or chlorine (Cl) [low (PAA:6ppm, Cl:2-4 ppm) or high (PAA:10 ppm, Cl:10-12 ppm) residual concentrations] for an allotted contact time (1, 5, or 10 min). Strains were enumerated, and a log-linear model was used to characterize how treatment combinations influenced reductions. All Cl treatment combinations achieved a ≥3 log10 CFU/100 mL reduction, regardless of strain (3.43 ± 0.25 to 7.05 ± 0.00 log10 CFU/100 mL). Approximately 80% (19/24) and 67% (16/24) of PAA treatment combinations achieved a ≥3 log10 CFU/100 mL for STEC and E. coli TVS 353, respectively. The log-linear model showed contact time (10 > 5 > 1 min) and sanitizer type (Cl > PAA) had the greatest impact on STEC and E. coli TVS 353 reductions (p < 0.001). E. coli TVS 353 in water samples was more resistant to sanitizer treatment (p < 0.001) indicating applicability as a good surrogate. Results demonstrated Cl and PAA can be effective agricultural water treatment strategies when sanitizer chemistry is managed. These data will assist with the development of in-field validation studies and may identify suitable candidates for the registration of antimicrobial pesticide products for use against foodborne pathogens in preharvest agricultural water treatment.

Wheat craft beer made from AFB1-contaminated wheat malt contains detectable mycotoxins, retains quality attributes, but differs in some fermentation metabolites.

Levels of aflatoxin B1 (AFB1) were measured during the production of wheat craft beer made with wheat malt contaminated with AFB1 (1.23 µg/kg). A wheat craft beer made with non-contaminated wheat malt was produced for comparison purposes. AFB1 was measured after mashing (malt after the mashing process), and in spent grain (spent grains are filtered to collect the wort - remaining sugar-rich liquid), sweet wort, green beer, spent yeast, and in beer. Physicochemical parameters (pH, titratable acidity, color parameters, total soluble solids), sugars, organic acids, alcohols, and phenolics were evaluated after mashing, and in sweet wort, green beer, and beer samples. Density and yeast counts were determined over 120 h of sweet wort fermentation every 24 h. The AFB1 levels in the final beer were 0.22 µg/L, while the spent grains and spent yeasts contained 0.71 ± 0.17 and 0.11 ± 0.03 µg/kg of AFB1, respectively. AFB1 contamination did not influence the final product's physicochemical parameters, density during fermentation, fructose, or glycerol content. Higher yeast counts were observed during the first 48 h of non-contaminated wheat craft beer fermentation, with higher ethanol, citric acid, and propionic acid contents and lower glucose, malic acid, and lactic acid contents compared with beer contaminated with AFB1. Non-contaminated wheat craft beer also had higher concentrations of gallic acid, chlorogenic acid, catechin, procyanidin A2, and procyanidin B1. AFB1 contamination of wheat malt may not affect basic quality parameters in wheat craft beer but can influence the final product's organic acid and phenolic contents. Our findings show that if wheat craft beer is made with contaminated malt, AFB1 can remain in the final product and may pose a risk to consumers.

Ranking Food Safety Priorities of the Fresh Produce Industry in the United States.

A broad understanding of community member food safety priorities in the fresh produce supply chain does not currently exist. This information is essential to improve food safety knowledge and practices effectively and efficiently throughout the fresh produce industry; therefore, the goal of this study was to identify and rank community produce safety priorities in the United States. Survey questions were designed and approved by food safety experts for participants to rank 24 fresh produce safety priorities. The anonymous survey was distributed online via Qualtrics™ to fresh produce community members from November 2020 to May 2021. A score was calculated for each priority by summing weighted ranking scores across responses. Descriptive statistics and logistic regression were used to determine frequencies and distribution of response and identify factors (e.g., role in produce safety, size/location of organization/operation) that influenced rankings. A total of 281 respondents represented fourteen different roles in the fresh produce industry, with most identified as growers (39.5%). Produce operations were distributed across the U.S. and annual produce sales ranged from below $25,000 to over $5,000,000. Health and hygiene, training, postharvest sanitation, traceability, and harvest sanitation were ranked as the top five food safety priorities. These findings provide insight into community member priorities in fresh produce safety and can be used to inform intervention efforts, ranging from specialized training for produce growers and packers, industry-driven research projects, and gaps in risk communication strategies.

Growth models for Salmonella, E. coli O157:H7 and L. monocytogenes give different predictions for pathogen growth in cut leafy greens transportation, but are consistent in identifying higher risk conditions.

Leafy greens are frequently implicated in foodborne disease outbreaks and cut-leafy greens are a food that requires time and temperature control for safety. Predictive microbiology uses mathematical models to predict the growth of bacteria based on environmental conditions. The objective of our study was to compare published square root growth models for Salmonella (n = 6), pathogenic E. coli (n = 6) and Listeria monocytogenes (n = 4) using real world transport temperature data. Data from trucks transporting fresh-cut leafy greens during cross-country shipments were used as temperature inputs to the models. Bacterial growth was computed using the temperatures from each probe in every truck over the duration of transit, which resulted in 12-18 growth predictions per truck for each model. Each model generally gave significantly different predictions than other models for the same organism. The exception was for the two Salmonella models predicting the least growth and the two Salmonella models predicting the most growth which gave predictions that were not significantly different. Although different models tended to give different predictions, their ability to rank risk by truck was generally consistent across models. While absolute risk might be dependent upon choice of model, relative risk is independent of model choice.

Efficacy of cold plasma-activated water as an environmentally friendly sanitizer in egg washing.

Eggs in the United States are typically washed using chemical sanitizers such as quaternary ammonia (QA) or chlorine. Such treatments generate wash water, which could be potentially hazardous to the environment. A novel, nonthermal sanitization technique for washing shell eggs using cold plasma-activated water (PAW) was investigated in this study. The inactivation efficacy of PAW on Klebsiella michiganensis and the impact of PAW on the cuticle of the eggshell and shell strength were tested in comparison to QA. Washing inoculated eggs with PAW and QA achieved a similar microbial reduction (>5.28 log CFU/egg). Colorimetric analysis showed that ∆E-value for PAW-treated eggs was significantly lower than QA-treated eggs, suggesting higher cuticle coverage in eggs treated with PAW. The texture analysis to test for shell egg strength indicated that washing eggs with PAW did not affect the structural integrity of the eggshell when compared to eggs washed with QA. According to this study, PAW has the potential as an alternative to commercial sanitizers like QA in the egg-washing industry. PAW does not detrimentally impact shell strength or cuticle coverage and provides similar microbial reduction efficacy.

Microbiological Quality and Safety of Pizza Held Out of Temperature Control in University Dining Halls.

Pizza is a popular food consumed around the world every day. Hot food temperatures were obtained from 19,754 nonpizza samples and 1,336 pizza temperatures were taken from dining facilities operated by Rutgers University between 2001 and 2020. These data showed that pizza was more frequently out of temperature control than many other foods. A total of 57 pizza samples that were out of temperature control were collected for further study. Pizza was tested for total aerobic plate count (TPC), Staphylococcus aureus, Bacillus cereus, Lactic acid bacteria, coliforms, and Escherichia coli. Water activity of pizza and surface pH of each individual pizza component (topping, cheese, bread) were measured. Predictions for the growth of four relevant pathogens were made for select pH and water activity values using ComBase. Rutgers University dining hall data show only about 60% of all foods that are pizza are held at the appropriate temperature. When pizza contained detectable microorganisms (∼70% of samples), average TPC ranged from 2.72 log CFU/g to 3.34 log CFU/g. Two pizza samples contained detectable S. aureus (∼50 CFU/g). Two other samples contained B. cereus (∼50 and 100 CFU/g). Five pizza samples contained coliforms (4-9 MPN/g), and no E. coli were detected. Correlation coefficients (R2 values) for TPC and pickup temperature are quite low (<0.06). Based on the pH and water activity measurements, most (but not all) of the pizza samples would be considered to potentially require time temperature control for safety. The modeling analysis shows that the organism most likely to pose a risk would be S. aureus, and the largest magnitude increase predicted is 0.89 log CFU at 30°C, pH 5.52, and water activity 0.963. The overall conclusion from this study is that while pizza represents a theoretical risk, the actual risk would likely only manifest for pizza samples that are held out of temperature control for time periods of more than eight hours.

Estimation of Bacteriophage MS2 Inactivation Parameters During Microwave Heating of Frozen Strawberries.

Frozen berries have been repeatedly linked to acute gastroenteritis caused by norovirus, the most common cause of foodborne illness in the United States. Many guidelines recommend that frozen berries be microwaved for at least 2 min, but it is unclear if this thermal treatment is effective at inactivating norovirus. The objective of this study was to model the effect of microwave heating at varying power levels on the survival of bacteriophage MS2, a norovirus surrogate, when inoculated onto frozen strawberries. Bacteriophage MS2 was inoculated onto the surface of frozen strawberries with a starting concentration of approximately 10 log PFU/g. Samples (either 3 or 5 whole strawberries) were heated in a 1300-Watt domestic research microwave oven (frequency of 2450 MHz) at power levels of 30, 50, 70, and 100% (full power), for times ranging from 15 to 300 s to determine inactivation. Temperatures at berry surfaces were monitored during heating using fiberoptic thermometry. All experiments were conducted in triplicate. The primary model for thermal inactivation was a log-linear model of logN vs. time. The secondary model was for a D-value decreasing linearly with temperature and an added term that was path-dependent on the thermal history. Parameters in the model were estimated using dynamic temperature history at the surface of the berry, via nonlinear regression using all data simultaneously. The root mean square error was ∼0.5 PFU/g out of a total 6-log reduction. Log reductions of 1.1 ± 0.4, 1.5 ± 0.5, 3.1 ± 0.1, and 3.8 ± 0.2 log PFU/g were observed for 30, 50, 70, and 100% microwave power levels when three berries were heated for 60 s. D-values were 21.4 ± 1.95 s and 10.6 ± 1.1 s at 10 and 60°C, respectively. This work demonstrates an approach to estimate inactivation parameters for viruses from dynamic temperature data during microwave heating. These findings will be useful in predicting the safety effect of microwave heating of berries in the home or food service.

Curli Production Influences Cross-contamination by Escherichia coli O157:H7 When Washing Fresh-cut Romaine Lettuce.

Escherichia coli O157:H7 expresses extracellular proteins called curli that are essential for surface colonization. Transfer rates of E. coli O157:H7 0018+ (curli+), and 0018- (curli-) from inoculated to noninoculated lettuce pieces during washing were quantified in this study. Romaine lettuce pieces were inoculated with ∼6 log CFU on just the surface, just the cut edges, or both surface and cut edges. Samples were dried for 2 h in a biosafety cabinet and then washed with ten (10) noninoculated lettuce pieces in 500 mL of water for 30 s. The curli- strain was more readily removed (3 log reduction) compared to the curli+ (1 log reduction) when only the lettuce surface was inoculated (p > 0.05). The same was true when only the lettuce piece edge was inoculated (p > 0.05), although the magnitude of the reduction was less. There was no significant difference in reduction of curli+ strain between any of the surfaces. There was a significant difference (p < 0.05) in reduction of the curli- strains when comparing the leaf surface (more removal) to the cut leaf edge (less removal). The curli+ strain always showed significantly (p < 0.05) more transfer to noninoculated leaves regardless of the inoculation location. The curli+ strain transferred about -1 log percent (∼0.1%) to noninoculated pieces, while the curli- strain transferred about -2 log percent (∼0.01%) CFU to the noninoculated pieces. Mean log percent transfer was not significantly different within the curli+ or curli- experiments (p > 0.05). When the leaf surface was inoculated, there was about 2 log percent (i.e., close to 100% transfer) into the wash water for both the curli+ and curli- strains. When only the cut edges or surface and edge were inoculated, observed mean transfer rates were lower but not significantly different (p > 0.05). Further research is needed to more fully understand the factors that influence bacterial cross-contamination during the washing of fresh produce.

Efficacy of Grignard Pure to Inactivate Airborne Phage MS2, a Common SARS-CoV-2 Surrogate.

Grignard Pure (GP) is a unique and proprietary blend of triethylene glycol (TEG) and inert ingredients designed for continuous antimicrobial treatment of air. TEG has been designated as a ″Safer Chemical" by the US EPA. GP has already received approval from the US EPA under its Section 18 Public Health Emergency Exemption program for use in seven states. This study characterizes the efficacy of GP for inactivating MS2 bacteriophage─a nonenveloped virus widely used as a surrogate for SARS-CoV-2. Experiments measured the decrease in airborne viable MS2 concentration in the presence of different concentrations of GP from 60 to 90 min, accounting for both natural die-off and settling of MS2. Experiments were conducted both by introducing GP aerosol into air containing MS2 and by introducing airborne MS2 into air containing GP aerosol. GP is consistently able to rapidly reduce viable MS2 bacteriophage concentration by 2-3 logs at GP concentrations of 0.04-0.5 mg/m3 (corresponding to TEG concentrations of 0.025 to 0.287 mg/m3). Related GP efficacy experiments by the US EPA, as well as GP (TEG) safety and toxicology, are also discussed.

Thermal Inactivation of Salmonella enterica and Nonpathogenic Bacterial Surrogates in Wheat Flour by Baking in a Household Oven.

ABSTRACT: Wheat flour has been implicated in recalls and outbreaks linked to Salmonella and pathogenic Escherichia coli. An instructional online video posted on a popular YouTube channel with over 20 million subscribers claimed that safe raw cookie dough could be made from flour baked in a household oven at 177°C (350°F) for 5 min, but no evidence in support of that claim was provided. This study was conducted to assess thermal inactivation of two Salmonella strains, as well as Enterobacter aerogenes and Pantoea dispersa in wheat flour during home oven baking. Wheat flour was inoculated with Salmonella Enteritidis PT 30, Salmonella Typhimurium PT 42, or their potential surrogates at high concentrations (4.8 to 6.1 log CFU/g) before baking in a consumer-style convection oven (toaster oven) at 149, 177, and 204°C (300, 350, or 400°F) for up to 7 min. Flour was heated in an aluminum tray, with a maximum depth of ∼2 cm. Heated wheat flour samples (5 g each) were enumerated in triplicate, and the microbial concentration was expressed in log CFU per gram. Thermal profiles of the geometric center of the wheat flour pile and air in the oven during the baking were recorded. Water activity of wheat flour samples was also measured before and after baking. The water activity of wheat flour decreased, as baking temperature and time increased. Water activity values ranged from 0.30 to 0.06 after 7 min, as oven temperature increased from 149 to 204°C. Thermal inactivation kinetics were linear until counts approached the limit of detection for all microorganisms. D-values for Salmonella and potential surrogate strains ranged from 1.86 to 2.13 min at 149°C air temperature, 1.66 to 1.92 min at 177°C air temperature, and 1.12 to 1.38 min at 204°C air temperature. Both Salmonella strains and surrogates showed similar inactivation patterns. Baking of wheat flour in household toaster ovens has potential as an inactivation treatment of pathogenic bacteria in consumer homes, despite its low water activity.

Enterobacter aerogenes B199A May Be an Effective Surrogate for Quantifying Transfer of Salmonella Newport 96E01152C-TX from Cucumber Peel to Edible Flesh and Peeler during Peeling.

ABSTRACT: Fresh cucumbers have been linked to multistate outbreaks of salmonellosis in the United States. Cutting, slicing, shredding, or peeling can transfer pathogens from the surface of fresh produce to the edible flesh portion through tools or hands. Different nonpathogenic surrogates have been used in various intervention studies to predict Salmonella behavior. Little is known about the degree to which pathogens or their surrogates can transfer from the surface of fresh produce to edible flesh during peeling. This study quantifies the transfer of Salmonella Newport from the surface of cucumber to the edible flesh portion or peeler during peeling and evaluates Enterobacter aerogenes B199A, as well as native mesophilic microbiota, as surrogates for Salmonella transfer. Cucumbers were dip inoculated with Salmonella Newport or E. aerogenes at 7 log CFU per cucumber. Half of each inoculated cucumber was hand peeled by using a sterilized peeler, resulting in four separate samples (unpeeled half, edible flesh half, removed peel, and used peeler) to quantify bacterial transfer. Most (>95%) of inoculated E. aerogenes, Salmonella, or native mesophilic microbiota generally remained associated with the peel during peeling. E. aerogenes transfer to cucumber flesh ranged from 0.02 to 12.9%, while transfer to the peeler ranged from 0.01 to 6.6%. Salmonella to cucumber flesh ranged from 0 to 0.6%, while transfer to the peeler ranged from 0 to 2.2%. Native microflora transfer to cucumber flesh ranged from 0.02 to 3.7%, while transfer to the peeler ranged from 0.04 to 3.7%. The log percent transfer of E. aerogenes at 24 h, as well as several shorter times, was not significantly different (P > 0.05) from that of Salmonella transferred to the edible flesh portion or peeler during peeling. E. aerogenes B199A may be a useful surrogate for Salmonella in cross-contamination studies and may help guide future risk management efforts to reduce pathogen risk associated with fresh cucumbers.

Modeling the Growth of Salmonella on Sliced Cucumbers as a Function of Temperature and Relative Humidity.

ABSTRACT: Recent multistate outbreaks of salmonellosis linked to fresh cucumbers underscore the importance of understanding Salmonella behavior on cucumbers under different storage conditions. No validated models that describe the impact of environmental factors on the growth of Salmonella on sliced cucumbers currently exist. This study developed mathematical models to predict the growth of Salmonella on sliced cucumbers at different temperature and relative humidity (RH) conditions. Sliced cucumbers were inoculated with a four-strain cocktail of Salmonella and placed in desiccators containing a saturated salt solution to create controlled RH environments (∼15, 50, and 100% RH) at 7, 14, and 21°C for up to 120 h. Predictive models were developed by using the Baranyi and Roberts equation as a primary model, and estimated kinetic parameters were fitted into a square root (or Ratkowsky) equation for secondary models. The maximum growth rates for Salmonella on sliced cucumbers depended on temperature but not RH. The square root model for Salmonella growth was √µ= 0.0297 × (T - 6.5185), with a high R2 value (0.98). The models in this study will be useful for future microbial risk assessments and predictions of Salmonella behavior in the cucumbers to manage the risk of Salmonella on sliced cucumbers.

Draft Genome Sequence for Klebsiella michiganensis B199A, Originally Identified as Enterobacter aerogenes.

Here, we report the draft genome sequence of a strain of Klebsiella michiganensis originally identified as Enterobacter aerogenes B199A. This strain has been used as a Salmonella surrogate to study the effectiveness of handwashing and measure cross-contamination to and from a wide variety of surfaces and foods.

Initial and Final Cell Concentrations Significantly Influence the Maximum Growth Rate of Listeria monocytogenes in Published Literature Data for Whole Intact Fresh Produce.

ABSTRACT: Listeria monocytogenes has shown the ability to grow on fresh uncut produce; however, the factors that control growth are not well understood. Peer-reviewed journal articles (n = 29) meeting the inclusion criteria and related to the growth of L. monocytogenes on fresh produce were found through university library databases and Google Scholar searches. Growth models were fit to each of the extracted 130 data sets to estimate log CFU per day rates of growth by using the DMFit tool. Multiple linear stepwise regression models for factors influencing growth rate were developed using R software. Factors included were temperature, nutrient level of inoculation buffer, initial cell concentration, final cell concentration, inoculation method, container permeability, and surface characteristics. The full model produced adjusted R2, Akaike information criterion, and root mean square error values of 0.41, 488, and 1.61, respectively. Stepwise regression resulted in a reduced model with parameters for incubation temperature, inoculation buffer type, initial and final cell concentrations, container characteristics, and produce surface characteristics. Model fit statistics improved slightly in the reduced model. A further reduced three-parameter model included storage temperature and initial and final cell concentrations, with interaction terms. This three-parameter model had adjusted R2, Akaike information criterion, and root mean square error values of 0.66, 417, and 1.24, respectively. Incubation temperature (P = 1.00E-09) initial cell concentration (P = 3.05E-12), and final cell concentration (P = 4.17E-09) all had highly significant effects on maximum growth rate. Our findings show the importance of inoculum concentration and produce microbial carrying capacity on the estimated growth rate and highlight the overall importance that temperature has on growth rate. Future experiments should consider initial inoculum concentration carefully when conducting growth studies for L. monocytogenes on whole produce.