Foodborne Illness Outbreaks Research Articles

MICROBIOLOGICAL QUALITY OF LEAFY GREEN VEGETABLES GROWN IN THE TOLUCA VALLEY

The intake of fresh fruits and vegetables has increased in recent years, as have outbreaks of foodborne illnesses associated with these products. The risk of microbiological hazards in vegetables can occur from the field to the table. The main sources of contamination are agricultural soil and irrigation water, which can affect product quality and be a reservoir of foodborne pathogenic bacteria. This research analysed the microbiological quality of green leafy vegetable crops: spinach (Spinacia oleracea L.), lettuce (Lactuca sativa L.) and coriander (Coriandrum sativum L.), grown in the valley of Toluca. The presence of microorganisms indicating microbiological contamination (mesophilic bacteria, total coliforms, faecal coliforms and Escherichia coli, Salmonella and Listeria) was evaluated in plants, water and soil. Sampling, processing, isolation and bacterial identification were performed in accordance with Mexican Official Standards and the FDA Bacteriological Analytical Manual. The recovered bacteria were subjected to biochemical tests, serotyping and PCR. Microbial counts were present in 100 % of the samples tested. The spinach culture had higher recovery of mesophilic bacteria and total coliforms, while the lettuce culture presented higher values for the faecal coliform group. The results indicated higher microbiological contamination in water and soil > 250 CFU for mesophilic bacteria, total coliforms and faecal coliforms, respectively. The microbiological counts of the three cultures were found within the maximum limits established by Mexican regulations. However, the presence of faecal coliforms, which included E. coli bacteria of serotype O105 ab flagellar, compromises the quality of the product and poses a risk to the health of the consumer.

Public Perceptions of Food Contamination Risks: A Simulation Experiment on the Psychological Impact of Incident Severity and Intentionality

ABSTRACT How do consumers perceive risks associated with food contamination? How do they respond to foodborne illness outbreaks and food recalls resulting from food contamination? We report findings from an experiment (N = 1,010) in which participants were exposed to a simulated news report on a food contamination incident that had led to a foodborne illness outbreak and voluntary food recalls. Two characteristics of the food contamination incident were experimentally manipulated – severity (i.e., how serious the consequences of the incident were) and intentionality (i.e., whether the incident was caused by an accident or an intentional act to harm). We found that higher severity generally led to higher risk perceptions and risk-reduction intentions. A contamination incident attributed to an intentional act to harm, as opposed to an accident, caused greater intentions to temporarily reduce consumption of the contaminated food and to seek out more information, but only when incident severity was relatively low. Implications of these findings for effectively communicating food contamination risks are discussed.

Regulation Mechanisms of Virulence Genes in Enterohemorrhagic Escherichia coli.

Enterohemorrhagic Escherichia coli (EHEC) is one of the most common E. coli pathotypes reported to cause several outbreaks of foodborne illnesses. EHEC is a zoonotic pathogen, and ruminants, especially cattle, are considered important reservoirs for the most common EHEC serotype, E. coli O157:H7. Humans are infected indirectly through the consumption of food (milk, meat, leafy vegetables, and fruits) and water contaminated by animal feces or direct contact with carrier animals or humans. E. coli O157:H7 is one of the most frequently reported causes of foodborne illnesses in developed countries. It employs two essential virulence mechanisms to trigger damage to the host. These are the development of attaching and effacing (AE) phenotypes on the intestinal mucosa of the host and the production of Shiga toxin (Stx) that causes hemorrhagic colitis and hemolytic uremic syndrome. The AE phenotype is controlled by the pathogenicity island, the locus of enterocyte effacement (LEE). The induction of both AE and Stx is under strict and highly complex regulatory mechanisms. Thus, a good understanding of these mechanisms, major proteins expressed, and environmental cues involved in the regulation of the expression of the virulence genes is vital to finding a method to control the colonization of reservoir hosts, especially cattle, and disease development in humans. This review is a concise account of the current state of knowledge of virulence gene regulation in the LEE-positive EHEC.

Effects of a novel combination of gallic acid, hydrogen peroxide and lactic acid on pathogen inactivation and shelf-life of baby spinach

Recurring foodborne illness outbreaks associated with the consumption of contaminated leafy greens attest to the challenges facing the produce industry. Here we report the effects of a novel combination of gallic acid (1500 mg/L), hydrogen peroxide (30 mg/L), and lactic acid (1800 mg/L) (GHL) on inactivation of foodborne human pathogens on baby spinach. Fresh baby spinach samples inoculated with Escherichia coli O157:H7 and Listeria monocytogenes were treated with the GHL formulation, chlorine (50 mg/L), peroxyacetic acid (80 mg/L), water, or remained unwashed. E. coli O157:H7 and L. monocytogenes populations on baby spinach and product quality and shelf-life were determined following treatments on processing day and during cold storage for up to 14 days. Washing baby spinach with GHL for 2 min reduced E. coli O157:H7 by 0.9 Log CFU/g while washing with chlorine and peroxyacetic acid reduced E. coli O157:H7 by 0.6 Log CFU/g. E. coli O157:H7 populations declined over time during cold storage in all treatment groups. However, GHL-treated samples maintained significantly lower E. coli O157:H7 populations throughout the storage period. On the other hand, all treated samples showed significantly reduced L. monocytogenes populations compared to water washed samples, while no significant difference was observed among GHL, chlorine, and peroxyacetic acid treatments. L. monocytogenes grew during storage and the difference in populations among all treatments was not significant. GHL washed samples showed slight browning (6 on a scale of 100) on rib edges and injured leaf surfaces, which disappeared within three days during storage. No other significant quality difference was observed among treatments. The results suggest that GHL can serve as an alternative to conventional sanitizers for fresh produce washing. GHL could be especially useful for the organic produce industry where the application of chlorine is limited.

Epidemiology, Serotype and Resistance of Salmonella Isolates from a Children's Hospital in Hangzhou, Zhejiang, China, 2006-2021.

PurposeThis research investigated the dynamics of antibiotic resistance in Salmonella and the epidemiology of Salmonella infection in children. These data can aid in the prevention and control of the Salmonella epidemic and the diagnosis and treatment of salmonellosis.MethodsIn this study, we retrospectively reviewed and analysed data regarding epidemiology, clinical symptoms, Salmonella serotypes, and antibiotic resistance from the medical records of patients with Salmonella infections in Hangzhou Children’s Hospital from April 2006 to December 2021.ResultsA total of 2099 Salmonella isolates were identified during the 16-year study period, and 98.6% (2069) of the isolates were isolated from stool. About 84.5% (1773/2099) of the total Salmonella isolates were detected from May to October. The median age of the 2099 children with Salmonella infection was 1.4 years (17 months) (IQR: 0.9–2.8 years). In 1572 (74.9%) patients, the course of the disease was limited to uncomplicated gastroenteritis. S. Typhimurium (805/2099, 38.4%) was predominant, followed by S. Enteritidis (290/2099, 13.8%). The total number of serotypes and the number of less common serotypes are increasing. Nontyphoid Salmonella that cause invasive infections, including S. Typhimurium, S. Stanley, and S. Choleraesuis, accounted for 60.0% (18/30). The Salmonella strains were resistant to ampicillin, ampicillin-sulbactam, trimethoprim-sulfamethoxazole, ceftriaxone, and ciprofloxacin at percentages of 71.5%, 51.5%, 36.5%, 22.4%, and 14.7%, respectively. No imipenem-resistant strains were identified. 24.8% of the isolates exhibited multidrug resistance (MDR).ConclusionS. typhimurium and S. enteritidis were the dominant serotypes in children (<2 years) with salmonella-infected arrhoea in Hangzhou, China. Ongoing serotype monitoring should be necessitated and dynamic changes in serotypes should be carefully examined to prevent the sudden outbreak of foodborne illness. Salmonella exhibits a higher rate of resistance to common antibiotics, and the risk of multidrug resistance should not be ignored. Therefore, clinicians should administer antibiotics judiciously according to the results of drug sensitivity tests.

A 2019 Outbreak Investigation of Hepatitis A Virus Infections in the United States Linked to Imported Fresh Blackberries.

Globally, hepatitis A virus (HAV) is one of the most common agents of acute viral hepatitis and causes approximately 1.4 million cases and 90,000 deaths annually despite the existence of an effective vaccine. In 2019, federal, state, and local partners investigated a multi-state outbreak of HAV infections linked to fresh blackberries sourced from multiple suppliers in Michoacán, Mexico. A total of 20 individuals with outbreak-related HAV infection were reported in seven states, including 11 hospitalizations, and no deaths. The Food and Drug Administration (FDA), the Centers for Disease Control and Prevention (CDC), and Nebraska State and Douglas County Health Departments conducted a traceback investigation for fresh blackberries reportedly purchased by 16 ill persons. These individuals reported purchasing fresh blackberries from 11 points of service from September 16 through 29, 2019 and their clinical isolates assessed through next-generation sequencing and phylogenetic analysis were genetically similar. The traceback investigation did not reveal convergence on a common grower or packing house within Mexico, but all of the blackberries were harvested from growers in Michoacán, Mexico. FDA did not detect the pathogen after analyzing fresh blackberry samples from four distributors, one consumer, and from nine importers at the port of entry as a result of increased screening. Challenges included gaps in traceability practices and the inability to recover the pathogen from sample testing, which prohibited investigators from determining the source of the implicated blackberries. This multi-state outbreak illustrated the importance of food safety practices for fresh produce that may contribute to foodborne illness outbreaks.

Effect of ultraviolet light treatment on microbiological safety and quality of fresh produce: An overview.

Fresh and fresh-cut fruits and vegetables have been associated in several foodborne illness outbreaks. Although investigations from those outbreaks reported that the contamination with pathogenic microorganisms may occur at any point in the farm to fork continuum, effective control strategies are still being widely investigated. In that direction, the concept of hurdle technology involving a sequence of different interventions have been widely explored. Among those interventions, ultraviolet (UV) light alone or in combination with other treatments such as use of organic acids or sanitizer solutions, has found to be a promising approach to maintain the microbiological safety and quality of fresh and fresh-cut produce. Recent advances in using UV as a part of hurdle technology on the safety of fresh produce at different stages are presented here. Furthermore, this review discusses the mechanism of UV induced antimicrobial activity, factors that influence antimicrobial efficacy and its effect on produce. In addition, the challenges, and prospects of using UV irradiation as an intervention treatment were also discussed.

Ability of Two Strains of Lactic Acid Bacteria To Inhibit Listeria monocytogenes by Spot Inoculation and in an Environmental Microbiome Context.

ABSTRACTWe evaluated the ability of two strains of lactic acid bacteria (LAB) to inhibit L. monocytogenes using spot inoculation and environmental microbiome attached-biomass assays. LAB strains (PS01155 and PS01156) were tested for antilisterial activity toward 22 phylogenetically distinct L. monocytogenes strains isolated from three fruit packing environments (F1, F2, and F3). LAB strains were tested by spot inoculation onto L. monocytogenes lawns (108 and 107 CFU/mL) and incubated at 15, 20, 25, or 30°C for 3 days. The same LAB strains were also cocultured at 15°C for 3, 5, and 15 days in polypropylene conical tubes with L. monocytogenes and environmental microbiome suspensions collected from F1, F2, and F3. In the spot inoculation assay, PS01156 was significantly more inhibitory toward less concentrated L. monocytogenes lawns than more concentrated lawns at all the tested temperatures, while PS01155 was significantly more inhibitory toward less concentrated lawns only at 15 and 25°C. Furthermore, inhibition of L. monocytogenes by PS01156 was significantly greater at 15°C than higher temperatures, whereas the temperature did not have an effect on the inhibitory activity of PS01155. In the assay using attached environmental microbiome biomass, L. monocytogenes concentration was significantly reduced by PS01156, but not PS01155, when cocultured with microbiomes from F1 and F3 and incubated for 3 days at 15°C. Attached biomass microbiota composition was significantly affected by incubation time but not by LAB strain. This study demonstrates that LAB strains that may exhibit inhibitory properties toward L. monocytogenes in a spot inoculation assay may not maintain antilisterial activity within a complex microbiome.IMPORTANCE Listeria monocytogenes has previously been associated with outbreaks of foodborne illness linked to consumption of fresh produce. In addition to conventional cleaning and sanitizing, lactic acid bacteria (LAB) have been studied for biocontrol of L. monocytogenes in food processing environments that are challenging to clean and sanitize. We evaluated whether two specific LAB strains, PS01155 and PS01156, can inhibit the growth of L. monocytogenes strains in a spot inoculation and in an attached-biomass assay, in which they were cocultured with environmental microbiomes collected from tree fruit packing facilities. LAB strains PS01155 and PS01156 inhibited L. monocytogenes in a spot inoculation assay, but the antilisterial activity was lower or not detected when they were grown with environmental microbiota. These results highlight the importance of conducting biocontrol challenge tests in the context of the complex environmental microbiomes present in food processing facilities to assess their potential for application in the food industry.

Foodborne Outbreak Rates Associated with Restaurant Inspection Grading and Posting at the Point of Service: Evaluation Using National Foodborne Outbreak Surveillance Data

A previously conducted national survey of restaurant inspection programs associated the practice of disclosing inspection results to consumers at the restaurant point of service (POS) with fewer foodborne outbreaks. We used data from the national Foodborne Disease Outbreak Surveillance System (FDOSS) to assess the reproducibility of the survey results. Programs that participated in the survey accounted for approximately 23% of the single-state foodborne illness outbreaks in restaurant settings reported to FDOSS during 2016 to 2018. Agencies that disclosed inspection results at the POS reported fewer outbreaks (mean = 0.29 outbreaks per 1,000 establishments) than those that disclosed results online (0.7) or not at all (1.0). Having any grading method for inspections was associated with fewer reported outbreaks than having no grading method. Agencies that used letter grades had the lowest numbers of outbreaks per 1,000 establishments. There was a positive association (correlation coefficient, R2 = 0.29) between the mean number of foodborne illness complaints per 1,000 establishments, per the survey, and the mean number of restaurant outbreaks reported to FDOSS (R2 = 0.29). This association was stronger for bacterial toxin-mediated outbreaks (R2 = 0.35) than for norovirus (R2 = 0.10) or Salmonella (R2 = 0.01) outbreaks. Our cross-sectional study findings are consistent with previous observations that linked the practice of posting graded inspection results at the POS with reduced occurrence of foodborne illnesses and outbreaks associated with restaurants. Support for foodborne illness surveillance programs and food regulatory activities at local health agencies is foundational for food safety systems coordinated at state and federal levels.

The live bacterial load and microbiota composition of prepacked “ready-to-eat” leafy greens during household conditions, with special reference to E. coli

Ready-to-eat (RTE) leafy greens are popular products that unfortunately have been associated with numerous foodborne illness outbreaks. Since the influence of consumer practices is essential for their quality and safety, the objective of this study was to analyze the microbiota of RTE products throughout shelf life during simulated household conditions. Products from different companies were analyzed in terms of plate counts, and resealed and unopened packages were compared. High bacterial loads were found, up to a total plate count of 9.6 log10 CFU/g, and Enterobacteriaceae plate counts up to 6.0 CFU/g on the expiration date. The effect of consumer practice varied, thus no conclusions regarding resealed or unopened bags could be drawn. The tested products contained opportunistic pathogens, such as Enterobacter homaechei, Hafnia paralvei and Pantoea agglomerans. Amplicon sequencing revealed that the relative abundance of major taxonomic groups changed during shelf life; Pseudomonadaceae and Xanthomonadaceae decreased, while Flavobacteriaceae and Marinomonadaceae inceased. Inoculation with E. coli CCUG 29300T showed that the relative abundance of Escherichia-Shigella was lower on rocket than on other tested leafy greens. Inoculation with E. coli strain 921 indicate growth at the beginning of shelf-life time, while E. coli 731 increases at the end, seemingly able to adapt to cold storage conditions. The high levels of live microorganisms, the detection of opportunistic pathogens, and the ability of E. coli strains to grow at refrigeration temperature raise concerns and indicate that the shelf life may be shortened to achieve a safer product. Due to variations between products, further studies are needed to define how long the shelf-life of these products should be, to ensure a safe product even at the end of the shelf-life period.

Electrochemical Biosensor for Rapid Detection of Listeria monocytogenes

Listeria monocytogenes (L. monocytogenes) is a common foodborne pathogen that has been responsible for many foodborne illness outbreaks in recent years. Currently, Listeria contamination in food products is identified only through molecular tests conducted in diagnostic laboratories. No established phage based diagnostic methods for L. monocytogenes during food production or processing are used. Here we report a potentially disruptive rapid diagnostic method based on electrochemical biosensing principles that use bacteriophages as bioreceptors for selective identification and quantification of L. monocytogenes. Electrochemical biosensors are good alternatives to molecular detection methods due to their ease of use, high specificity, sensitivity, and low cost. Bacteriophages can serve as excellent biorecognition elements in biosensors due to their robust stability in a range of environmental conditions and their ability to distinguish between live and dead bacterial cells. The impedimetric biosensing platform for L. monocytogenes detection was developed by immobilizing P100 bacteriophage onto quarternized polyethylenimine modified carbon nanotubes using an in-house developed molecular tethering method. The resulting sensor showed high selectivity and sensitivity toward L. monocytogenes with a limit of detection of 8.4 CFU/ml. Initial results demonstrate that the biosensing platform is highly reliable in its selectivity towards its target analyte, L. monocytogenes.

Foodborne Illness Outbreaks Reported to National Surveillance, United States, 2009-2018.

Foodborne outbreaks reported to national surveillance systems represent a subset of all outbreaks in the United States; not all outbreaks are detected, investigated, and reported. We described the structural factors and outbreak characteristics of outbreaks reported during 2009–2018. We categorized states (plus DC) as high (highest quintile), middle (middle 3 quintiles), or low (lowest quintile) reporters on the basis of the number of reported outbreaks per 10 million population. Analysis revealed considerable variation across states in the number and types of foodborne outbreaks reported. High-reporting states reported 4 times more outbreaks than low reporters. Low reporters were more likely than high reporters to report larger outbreaks and less likely to implicate a setting or food vehicle; however, we did not observe a significant difference in the types of food vehicles identified. Per capita funding was strongly associated with increased reporting. Investments in public health programming have a measurable effect on outbreak reporting.

Foodborne Illness Outbreak Severity Across Geographic and Supply Chain Contamination Locations in the United States, 2009–2019

ObjectivesIn 2009, the Centers for Disease Control and Prevention's National Outbreak Reporting System (NORS) began collecting supply chain contamination data as part of foodborne outbreak (FBO) traceback investigations. We created an integrated FBO severity score measure and examined differences in FBO severity by geographic and supply chain contamination locations. We used 9,407 NORS records between 2009–2019 to demonstrate the utility of the proposed methodology.MethodsThe severity scores were composed of 11 metrics based on outbreak intensity and duration characteristics and metrics’ completeness. Metrics were normalized (with natural log-transformation), calibrated (to 0–1 scale), and weighed (by completeness) across all recorded outbreaks. Individual outbreak scores ranged from 0 (lowest severity) to 1 (highest severity). We compared averages of severity scores across geographic (i.e., multistate and single state exposure outbreak) and supply chain contamination locations (i.e., suspected or confirmed before preparation, preparation, unknown and missing) using tobit-regression models.ResultsAll FBOs reported the state of exposure; 5,500 (58.5%) reported supply chain contamination location. Multistate exposure FBOs had higher median severity scores than single state outbreaks (0.54 [0.44, 0.67] vs 0.28 [0.16, 0.41], P < 0.001). FBOs with reported point of contamination that occurred before preparation had higher median severity scores than all other stages (0.36 [0.27, 0.49] vs 0.26 [0.15, 0.41], 0.25 [0.13, 0.39], and 0.29 [0.16, 0.43], P < 0.001, for preparation, unknown and missing stages respectively).ConclusionsUnderstanding an FBO's severity by geographic and supply chain contamination location helps to quantify supply chain vulnerability and improve monitoring of food safety. Identification of supply chain contamination at high level granularity and completeness is critical for developing foodborne outbreak (FBO) prediction analytics aimed to reduce both the volume and severity of outbreaks and illnesses.Funding SourcesDoD, ODNI, NIFA, NSF, USIAD.

Effects of pulsed light and aerosolized formic acid treatments on inactivation of Salmonella enterica on cherry tomato, reduction of microbial loads, and preservation of fruit quality

Fresh produce remains the leading cause of foodborne illness outbreaks. Novel nonthermal technologies are needed to reduce the risk of pathogen contamination. The objective of this study was to develop a novel intervention technology exploiting integration of high intensity short time (10 s) pulsed light (PL) and aerosolized formic acid (AFA) for inactivation of Salmonella and maintenance of quality of cherry tomato. Smooth surface of tomatoes, inoculated with a cocktail containing three serotypes of Salmonella enterica, was treated with PL for 10 s followed by 2 min treatment with 1% AFA. Non-inoculated tomatoes were used to study the treatment effects on native microflora and quality. PL delivered significant inactivation at low doses. An optimal 10 s PL treatment equivalent to a dose of 10.5 J/cm2, provided 2.2 log CFU/g reduction while a 2 min exposure in 1% AFA antimicrobial yielded comparatively low, 1.7 log CFU/g reductions of Salmonella on tomato. The combination treatments of PL (10 s) followed by 1% AFA (2 min) provided additive inactivation yielding 4.2 log CFU/g reductions (P ≤ 0.05) of the pathogen. During cold storage (10 °C) the survivor population declined further providing 4.8 log CFU/g reductions on day 21. The combination PL-AFA treatment significantly reduced the native microbiota of tomato and also hindered their growth while in storage for three weeks. Mold and yeast (M&Y) spoilage organism populations declined to below the detection level. Furthermore, the quality factors as firmness and color of tomatoes were not significantly affected by the combination treatments. The treatment boosted the redness appearance of tomatoes indicating favorable consumer acceptability. Overall, our results demonstrate that combination of PL and AFA treatment could potentially be used as a novel approach to enhance microbial safety and quality of tomatoes.

Sample-in-answer-out colorimetric detection of Salmonella typhimurium using non-enzymatic cascade amplification

Rapid and sensitive screening of pathogens is a key to prevent the outbreak of foodborne illnesses. Herein, a new colorimetric immunoassay was proposed based on the release of Ag+ ions from AgNPs and the inhibition of PtNPs, and its supporting microfluidic platform was developed to automatically perform the whole bacterial detection procedure using Raspberry Pi and smartphone App. First, the immune AgNPs and magnetic nanobeads (MNBs) were used to conjugate with Salmonella typhimurium. Then, H2O2 was used to etch the AgNPs for release Ag+ ions. Finally, the colorimetric signal was greatly diminished because of the specific and efficient inhibition of Ag+ toward the peroxidase-like activity of the PtNPs. This colorimetric immunoassay showed a good specificity and an ultralow detection limit of 16.8 CFU/mL, which was about 3 orders of magnitude improvement compared with conventional ELISA, and the averaged recovery for the spiked chicken samples was 95.6%. The combination of this immunoassay with this microfluidic platform might be promising for rapid and sensitive screening of foodborne pathogens to ensure food safety.

Nonsynonymous Mutations in fepR Are Associated with Adaptation of Listeria monocytogenes and Other Listeria spp. to Low Concentrations of Benzalkonium Chloride but Do Not Increase Survival of L. monocytogenes and Other Listeria spp. after Exposure to Benzalkonium Chloride Concentrations Recommended for Use in Food Processing Environments.

ABSTRACTSelection for Listeria monocytogenes strains that are tolerant to quaternary ammonium compounds (such as benzalkonium chloride [BC]) is a concern across the food industry, including in fresh produce processing environments. This study evaluated the ability of 67 strains of produce-associated L. monocytogenes and other Listeria spp. (“parent strains”) to show enhanced BC tolerance after serial passaging in increasing BC concentrations and to maintain this tolerance after substreaking in the absence of BC. After serial passaging in BC, 62/67 “BC passaged cultures” showed higher MICs (4 to 20 mg/L) than parent strains (2 to 6 mg/L). After the substreaking of two isolates from BC passaged cultures for each parent strain, 105/134 “adapted isolates” maintained MICs (4 to 6 mg/L) higher than parent strain MICs. These results suggested that adapted isolates acquired heritable adaptations that confer BC tolerance. Whole-genome sequencing and Sanger sequencing of fepR, a local repressor of the MATE family efflux pump FepA, identified nonsynonymous fepR mutations in 48/67 adapted isolates. The mean inactivation of adapted isolates after exposure to use-level concentrations of BC (300 mg/L) was 4.48 log, which was not significantly different from inactivation observed in parent strains. Serial passaging of cocultures of L. monocytogenes strains containing bcrABC or qacH did not yield adapted isolates that showed enhanced BC tolerance in comparison to that of monocultures. These results suggest that horizontal gene transfer either did not occur or did not yield isolates with enhanced BC tolerance. Overall, this study provides new insights into selection of BC tolerance among L. monocytogenes and other Listeria spp.IMPORTANCE Listeria monocytogenes tolerance to quaternary ammonium compounds has been raised as a concern with regard to L. monocytogenes persistence in food processing environments, including in fresh produce packing and processing environments. Persistence of L. monocytogenes can increase the risk of product contamination, food recalls, and foodborne illness outbreaks. Our study shows that strains of L. monocytogenes and other Listeria spp. can acquire heritable adaptations that confer enhanced tolerance to low concentrations of benzalkonium chloride, but these adaptations do not increase survival of L. monocytogenes and other Listeria spp. when exposed to concentrations of benzalkonium chloride used for food contact surface sanitation (300 mg/L). Overall, these findings suggest that the emergence of benzalkonium chloride-tolerant Listeria strains in food processing environments is of limited concern, as even strains adapted to gain higher MICs in vitro maintain full sensitivity to the concentrations of benzalkonium chloride used for food contact surface sanitation.

Seed inoculation with antagonistic bacteria limits occurrence of E. coli O157:H7gfp + on baby spinach leaves

BackroundDuring the last decades, outbreaks of foodborne illnesses have increasingly been linked to fresh and/or minimally processed fruit and vegetables. Enterohemorrhagic Escherichia coli was the causal agent for major outbreaks in Europe with leafy green vegetables and sprouts. To improve food safety, microbial antagonism has received attention during recent years and could be one of the solution to prevent contamination of food borne pathogens on fresh produce. Here we investigate the antagonistic effect of three bacterial strains (Pseudomonas orientalis, P. flavescens and Rhodococcus sp.) isolated from spinach leaves against E. coli O157:H7gfp + under laboratory and greenhouse conditions.ResultsOur results shows that significantly less culturable E.coli O157:H7gfp + were retrieved from the spinach canopy subjected to antagonist seed treatment than canopy inoculation. Seeds inoculated with Rhodococcus sp. significantly reduced growth of E. coli O157:H7gfp + compared with the other antagonists. The result from the in vitro study shows a significant reduction of growth of E. coli O157:H7gfp+, but only after 44 h when E. coli O157:H7gfp + was propagated in a mixture of spent media from all three antagonists.ConclusionsThe antagonistic effect on phyllospheric E.coli O157:H7gfp + observed after seed inoculation with Rhodococcus sp. might be an indication of induced resistance mechanism in the crop. In addition, there was a small reduction of culturable E.coli O157:H7gfp + when propagated in spent media from all three antagonists. Nutritional conditions rather than metabolites formed by the three chosen organisms appear to be critical for controlling E. coli O157:H7gfp+.

Comparative immunomodulatory effects in mice and in human dendritic cells of five bacterial strains selected for biocontrol of leafy green vegetables

The market for ready-to eat vegetables is increasing, but unfortunately so do the numbers of food-borne illness outbreaks related to these products. A previous study has identified bacterial strains suitable for biocontrol of leafy green vegetables to reduce the exposure to pathogens in these products. As a tentative safety evaluation, five selected strains (Rhodococcus cerastii MR5x, Bacillus coagulans LMG P-32205, Bacillus coagulans LMG P-32206, Pseudomonas cedrina LMG P-32207 and Pseudomonas punonensis LMG P-32204) were individually compared for immunomodulating effects in mice and in human monocyte-derived dendritic cells (MoDCs). Mice receiving the two B. coagulans strains consistently resemble the immunological response of the normal control, and no, or low, cell activation and pro-inflammatory cytokine expression was observed in MoDCs exposed to B. coagulans strains. However, different responses were seen in the two models for the Gram-negative P. cedrina and the Gram-positive R. cerastii. Moreover, P. punonensis and B. coagulans increased the microbiota diversity in mice as seen by the Shannon-Wiener index. In conclusion, the two strains of B. coagulans showed an immunological response that indicate that they lack pathogenic abilities, thus encouraging further safety evaluation and showing great potential to be used as biocontrol agents on leafy green vegetables.

Colorimetric food spoilage monitoring with carbon dot and UV light reinforced fish gelatin films using a smartphone application

The objective of this study was to develop novel colorimetric films for food freshness monitoring. UV light irradiation (365 nm) and carbon dots (CDs) were tested as the potential crosslinkers in the fabrication of anthocyanins doped fish gelatin (FG) films. The effect of crosslinkers on the optical, surface, structural, barrier and mechanical properties of FG films was investigated. The incorporation of CDs under UV irradiation improved the tested properties of FG films. The kinetic colorimetric responses of FG films against ammonia vapor were studied to simulate the food spoilage and determine the ammonia sensitivity of the films. Among the tested films, UV-treated FG films containing 100 mg/l (FG-UV-CD100) indicated the best properties. Later, the color difference of FG-UV-CD100 films was observed to correlate well with microbial growth and TVB-N release in skinless chicken breast samples. At the same time, a custom-designed smartphone application (SmartFood) was developed to be used with the FG-UV-CD100 film for quantitative estimation of food freshness in real-time. The proposed food freshness monitoring platform reveals a great potential to minimize global food waste and the outbreak of foodborne illness.

Biocontrol of Listeria monocytogenes and Salmonella enterica on Fresh Strawberries with Lactic Acid Bacteria During Refrigerated Storage.

Small fruits such as strawberries have been increasingly implicated in outbreaks of foodborne illnesses. Salmonella enterica and Listeria monocytogenes may contaminate strawberries leading to potential public health concern. The objective of this study was to investigate the efficacy of a combined lactic acid bacteria (LAB) treatment of Lactobacillus plantarum and Pediococcus pentosaceus for controlling S. enterica and L. monocytogenes on fresh strawberries during storage at 4°C and 10°C. Strawberries purchased from a local grocery store were separately dip inoculated with Salmonella Newport, Salmonella Tennessee, Salmonella Thompson, or a three-strain cocktail of L. monocytogenes at ∼9 log colony-forming unit (CFU)/mL and allowed to air-dry for 1 h. Inoculated strawberries were then divided into three groups: (1) Control (pathogen alone), (2) Man, Rogosa, Sharpe (MRS) control (dipping in MRS broth), and (3) LAB treatment (dipping in a LAB cocktail of L. plantarum and P. pentosaceus). After treatment, strawberries were stored at 4°C or 10°C for 7 d in vented clamshell containers. Surviving Listeria, Salmonella, and LAB populations on strawberries were determined on 0, 1, 3, and 7 d post-treatment by plating on selective agars. At both 4°C and 10°C, LAB treatment significantly decreased Listeria populations by up to 2 log CFU/g compared to controls after 3 d of storage (p < 0.05). When strawberries were stored at 4°C, LAB treatment reduced ∼2.5 log, ∼2.7 log, and ∼2.9 log CFU/g in Salmonella Newport, Salmonella Tennessee, and Salmonella Thompson populations, respectively, compared to control on day 7. Similarly, ∼2.5 log CFU/g reductions of Salmonella populations were observed with LAB treatment at 10°C on day 7. LAB populations remained at ∼7.5 log CFU/g levels on strawberries at both temperatures throughout the entire study. Results of this study suggest that a combined LAB treatment can be potentially used as biocontrol agents against Salmonella and L. monocytogenes on strawberries at postharvest level.