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1.  Detection of Foodborne Bacterial Pathogens from Individual Filth Flies 
There is unanimous consensus that insects are important vectors of foodborne pathogens. However, linking insects as vectors of the pathogen causing a particular foodborne illness outbreak has been challenging. This is because insects are not being aseptically collected as part of an environmental sampling program during foodborne outbreak investigations and because there is not a standardized method to detect foodborne bacteria from individual insects. To take a step towards solving this problem, we adapted a protocol from a commercially available PCR-based system that detects foodborne pathogens from food and environmental samples, to detect foodborne pathogens from individual flies.Using this standardized protocol, we surveyed 100 wild-caught flies for the presence of Cronobacter spp., Salmonella enterica, and Listeria monocytogenes and demonstrated that it was possible to detect and further isolate these pathogens from the body surface and the alimentary canal of a single fly. Twenty-two percent of the alimentary canals and 8% of the body surfaces from collected wild flies were positive for at least one of the three foodborne pathogens. The prevalence of Cronobacter spp. on either body part of the flies was statistically higher (19%) than the prevalence of S. enterica (7%) and L.monocytogenes (4%). No false positives were observed when detecting S. enterica and L. monocytogenes using this PCR-based system because pure bacterial cultures were obtained from all PCR-positive results. However, pure Cronobacter colonies were not obtained from about 50% of PCR-positive samples, suggesting that the PCR-based detection system for this pathogen cross-reacts with other Enterobacteriaceae present among the highly complex microbiota carried by wild flies. The standardized protocol presented here will allow laboratories to detect bacterial foodborne pathogens from aseptically collected insects, thereby giving public health officials another line of evidence to find out how the food was contaminated when performing foodborne outbreak investigations.
PMCID: PMC4354650  PMID: 25742168
Environmental Sciences; Issue 96; Synanthropy; filth flies; Cronobacter; Listeria monocytogenes; Salmonella; Escherichia coli O157:H7; shiga-toxigenic E. coli; STEC; PCR-based methods; foodborne illness; foodborne outbreak investigations.
2.  Lytic bacteriophages 
Bacteriophage  2013;3(2):e25518.
Foodborne illnesses resulting from the consumption of produce commodities contaminated with enteric pathogens continue to be a significant public health issue. Lytic bacteriophages may provide an effective and natural intervention to reduce bacterial pathogens on fresh and fresh-cut produce commodities. The use of multi-phage cocktails specific for a single pathogen has been most frequently assessed on produce commodities to minimize the development of bacteriophage insensitive mutants (BIM) in target pathogen populations. Regulatory approval for the use of several lytic phage products specific for bacterial pathogens such as Escherichia coli O157:H7, Salmonella spp. and Listeria monocytogenes in foods and on food processing surfaces has been granted by various agencies in the US and other countries, possibly allowing for the more widespread use of bacteriophages in the decontamination of fresh and minimally processed produce. Research studies have shown lytic bacteriophages specific for E. coli O157:H7, Salmonella spp. and Listeria monocytogenes have been effective in reducing pathogen populations on leafy greens, sprouts and tomatoes.
PMCID: PMC3821672  PMID: 24228223
bacteriophages; lytic; leafy greens; melons; sprouts; produce; vegetables; Escherichia coli O157:H7; Salmonella; Listeria monocytogenes
3.  Food safety and foodborne disease in 21st century homes 
Over the past decade there has been a growing recognition of the involvement of the home in several public health and hygiene issues. Perhaps the best understood of these issues is the role of the home in the transmission and acquisition of foodborne disease. The incidence of foodborne disease is increasing globally. Although foodborne disease data collection systems often miss the mass of home-based outbreaks of sporadic infection, it is now accepted that many cases of foodborne illness occur as a result of improper food handling and preparation by consumers in their own kitchens. Some of the most compelling evidence has come from the international data on Salmonella species and Campylobacter species infections.
By its very nature, the home is a multifunctional setting and this directly impacts upon the need for better food safety in the home. In particular, the growing population of elderly and other immnocompromised individuals living at home who are likely to be more vulnerable to the impact of foodborne disease is an important aspect to consider. In addition, some developed nations are currently undergoing a dramatic shift in healthcare delivery, resulting in millions of patients nursed at home. Other aspects of the home that are unique in terms of food safety are the use of the home as a daycare centre for preschool age children, the presence of domestic animals in the home and the use of the domestic kitchen for small-scale commercial catering operations. At the global level, domestic food safety issues for the 21st century include the continued globalization of the food supply, the impact of international travel and tourism, and the impact of foodborne disease on developing nations.
A number of countries have launched national campaigns to reduce the burden of foodborne disease, including alerting consumers to the need to practice food safety at home. Home hygiene practice and consumer hygiene products are being refined and targeted to areas of risk, including preventing the onward transmission of foodborne illness via the inanimate environment. It has been said that food safety in the home is the last line of defense against foodborne disease, and it is likely that this will remain true for the global population in the foreseeable future.
PMCID: PMC2094945  PMID: 18159469
Food safety; Foodborne disease; Home
4.  Bacteriophages and Their Role in Food Safety 
The interest for natural antimicrobial compounds has increased due to alterations in consumer positions towards the use of chemical preservatives in foodstuff and food processing surfaces. Bacteriophages fit in the class of natural antimicrobial and their effectiveness in controlling bacterial pathogens in agro-food industry has led to the development of different phage products already approved by USFDA and USDA. The majority of these products are to be used in farm animals or animal products such as carcasses, meats and also in agricultural and horticultural products. Treatment with specific phages in the food industry can prevent the decay of products and the spread of bacterial diseases and ultimately promote safe environments in animal and plant food production, processing, and handling. This is an overview of recent work carried out with phages as tools to promote food safety, starting with a general introduction describing the prevalence of foodborne pathogens and bacteriophages and a more detailed discussion on the use of phage therapy to prevent and treat experimentally induced infections of animals against the most common foodborne pathogens, the use of phages as biocontrol agents in foods, and also their use as biosanitizers of food contact surfaces.
PMCID: PMC3536431  PMID: 23316235
5.  Prevention of bacterial foodborne disease using nanobiotechnology 
Foodborne disease is an important source of expense, morbidity, and mortality for society. Detection and control constitute significant components of the overall management of foodborne bacterial pathogens, and this review focuses on the use of nanosized biological entities and molecules to achieve these goals. There is an emphasis on the use of organisms called bacteriophages (phages: viruses that infect bacteria), which are increasingly being used in pathogen detection and biocontrol applications. Detection of pathogens in foods by conventional techniques is time-consuming and expensive, although it can also be sensitive and accurate. Nanobiotechnology is being used to decrease detection times and cost through the development of biosensors, exploiting specific cell-recognition properties of antibodies and phage proteins. Although sensitivity per test can be excellent (eg, the detection of one cell), the very small volumes tested mean that sensitivity per sample is less compelling. An ideal detection method needs to be inexpensive, sensitive, and accurate, but no approach yet achieves all three. For nanobiotechnology to displace existing methods (culture-based, antibody-based rapid methods, or those that detect amplified nucleic acid) it will need to focus on improving sensitivity. Although manufactured nonbiological nanoparticles have been used to kill bacterial cells, nanosized organisms called phages are increasingly finding favor in food safety applications. Phages are amenable to protein and nucleic acid labeling, and can be very specific, and the typical large “burst size” resulting from phage amplification can be harnessed to produce a rapid increase in signal to facilitate detection. There are now several commercially available phages for pathogen control, and many reports in the literature demonstrate efficacy against a number of foodborne pathogens on diverse foods. As a method for control of pathogens, nanobiotechnology is therefore flourishing.
PMCID: PMC4154891  PMID: 25249756
bacteriophage; pathogen control; detection; food safety
6.  Ingested Salmonella enterica, Cronobacter sakazakii, Escherichia coli O157:H7, and Listeria monocytogenes: transmission dynamics from adult house flies to their eggs and first filial (F1) generation adults 
BMC Microbiology  2015;15:150.
The mechanical transmission of pathogenic bacteria by synanthropic filth flies is widely recognized. While many studies report the fate and the temporospatial distribution of ingested foodborne bacteria by filth flies, there is little evidence about the transmission dynamics of ingested foodborne bacteria by adult house flies (Musca domestica) to their progeny. In this study, we fed parental house fly adults with food contaminated with low, medium, and high concentrations of Salmonella enterica, Cronobacter sakazakii, Escherichia coli O157:H7, and Listeria monocytogenes and evaluated the probability of transmission of these pathogens to house fly eggs and the surface and the alimentary canal of their first filial (F1) generation adults.
All foodborne pathogens were present in samples containing pooled house fly eggs. The probability of transmission was higher after parental house flies ingested food containing medium bacterial loads. Cronobacter sakazakii was 16, 6, and 3 times more likely to be transmitted to house fly eggs than S. enterica, E. coli O157:H7, and L. monocytogenes, respectively. Only S. enterica and C. sakazakii were transmitted to F1 generation adults and their presence was 2.4 times more likely on their body surfaces than in their alimentary canals. The highest probabilities of finding S. enterica (60 %) and C. sakazakii (28 %) on newly emerged F1 adults were observed after parental house flies ingested food containing medium and high levels of these pathogens, respectively.
Our study demonstrates that adult house flies that fed from food contaminated with various levels of foodborne bacteria were able to transmit those pathogens to their eggs and some were further transmitted to newly emerged F1 generation adults, enhancing the vector potential of these insects. Understanding the type of associations that synanthropic filth flies establish with foodborne pathogens will help to elucidate transmission mechanisms and possible ways to mitigate the spread of foodborne pathogens.
Electronic supplementary material
The online version of this article (doi:10.1186/s12866-015-0478-5) contains supplementary material, which is available to authorized users.
PMCID: PMC4520200
7.  Emerging foodborne diseases: an evolving public health challenge. 
Emerging Infectious Diseases  1997;3(4):425-434.
The epidemiology of foodborne disease is changing. New pathogens have emerged, and some have spread worldwide. Many, including Salmonella, Escherichia coli O157:H7, Campylobacter, and Yersinia enterocolitica, have reservoirs in healthy food animals, from which they spread to an increasing variety of foods. These pathogens cause millions of cases of sporadic illness and chronic complications, as well as large and challenging outbreaks over many states and nations. Improved surveillance that combines rapid subtyping methods, cluster identification, and collaborative epidemiologic investigation can identify and halt large, dispersed outbreaks. Outbreak investigations and case-control studies of sporadic cases can identify sources of infection and guide the development of specific prevention strategies. Better understanding of how pathogens persist in animal reservoirs is also critical to successful long-term prevention. In the past, the central challenge of foodborne disease lay in preventing the contamination of human food with sewage or animal manure. In the future, prevention of foodborne disease will increasingly depend on controlling contamination of feed and water consumed by the animals themselves.
PMCID: PMC2640074  PMID: 9366593
8.  Bacteriophage biocontrol of Listeria monocytogenes on soft ripened white mold and red-smear cheeses 
Bacteriophage  2011;1(2):94-100.
Soft-ripened cheeses belong to the type of food most often contaminated with Listeria monocytogenes, and they have been implicated in several outbreaks of listeriosis. Bacteriophages represent an attractive way to combat foodborne pathogens without affecting other properties of the food. We used the broad host range, virulent Listeria phage A511 for control of L. monocytogenes during the production and ripening phases of both types of soft-ripened cheeses, white mold (Camembert-type) cheese, as well as washed-rind cheese with a red-smear surface (Limburger-type). The surfaces of young, unripened cheese were inoculated with 101–103 cfu/cm2 L. monocytogenes strains Scott A (serovar 4b) or CNL 103/2005 (serovar 1/2a). Phage was applied at defined time points thereafter, in single or repeated treatments, at 3 × 108 or 1 × 109 pfu/cm2. With Scott A (103 cfu/cm2) and a single dose of A511 (3 × 108 pfu/cm2) on camembert-type cheese, viable counts dropped 2.5 logs at the end of the 21 day ripening period. Repeated phage application did not further inhibit the bacteria, whereas a single higher dose (1 × 109 pfu/cm2) was found to be more effective. On red-smear cheese ripened for 22 days, Listeria counts were down by more than 3 logs. Repeated application of A511 further delayed re-growth of Listeria, but did not affect bacterial counts after 22 days. With lower initial Listeria contamination (101–102 cfu/cm2), viable counts dropped below the limit of detection, corresponding to more than 6 logs reduction compared to the control. Our data clearly demonstrate the potential of bacteriophage for biocontrol of L. monocytogenes in soft cheese.
PMCID: PMC3278646  PMID: 22334865
Listeria monocytogenes; bacteriophage; food safety; soft-ripened cheese
9.  Phage Display-Derived Binders Able to Distinguish Listeria monocytogenes from Other Listeria Species 
PLoS ONE  2013;8(9):e74312.
The objective of this study was to produce phage display-derived binders with the ability to distinguish Listeria monocytogenes from other Listeria spp., which may have potential utility to enhance detection of Listeria monocytogenes. To obtain binders with the desired binding specificity a series of surface and solution phage-display biopannings were performed. Initially, three rounds of surface biopanning against gamma-irradiated L. monocytogenes serovar 4b cells were performed followed by an additional surface biopanning round against L. monocytogenes 4b which included prior subtraction biopanning against gamma-irradiated L. innocua cells. In an attempt to further enhance binder specificity for L. monocytogenes 4b two rounds of solution biopanning were performed, both rounds included initial subtraction solution biopanning against L. innocua. Subsequent evaluations were performed on the phage clones by phage binding ELISA. All phage clones tested from the second round of solution biopanning had higher specificity for L. monocytogenes 4b than for L. innocua and three other foodborne pathogens (Salmonella spp., Escherichia coli and Campylobacter jejuni). Further evaluation with five other Listeria spp. revealed that one phage clone in particular, expressing peptide GRIADLPPLKPN, was highly specific for L. monocytogenes with at least 43-fold more binding capability to L. monocytogenes 4b than to any other Listeria sp. This proof-of-principle study demonstrates how a combination of surface, solution and subtractive biopanning was used to maximise binder specificity. L. monocytogenes-specific binders were obtained which could have potential application in novel detection tests for L. monocytogenes, benefiting both the food and medical industries.
PMCID: PMC3769378  PMID: 24040227
10.  A Likelihood-Based Approach to Identifying Contaminated Food Products Using Sales Data: Performance and Challenges 
PLoS Computational Biology  2014;10(7):e1003692.
Foodborne disease outbreaks of recent years demonstrate that due to increasingly interconnected supply chains these type of crisis situations have the potential to affect thousands of people, leading to significant healthcare costs, loss of revenue for food companies, and—in the worst cases—death. When a disease outbreak is detected, identifying the contaminated food quickly is vital to minimize suffering and limit economic losses. Here we present a likelihood-based approach that has the potential to accelerate the time needed to identify possibly contaminated food products, which is based on exploitation of food products sales data and the distribution of foodborne illness case reports. Using a real world food sales data set and artificially generated outbreak scenarios, we show that this method performs very well for contamination scenarios originating from a single “guilty” food product. As it is neither always possible nor necessary to identify the single offending product, the method has been extended such that it can be used as a binary classifier. With this extension it is possible to generate a set of potentially “guilty” products that contains the real outbreak source with very high accuracy. Furthermore we explore the patterns of food distributions that lead to “hard-to-identify” foods, the possibility of identifying these food groups a priori, and the extent to which the likelihood-based method can be used to quantify uncertainty. We find that high spatial correlation of sales data between products may be a useful indicator for “hard-to-identify” products.
Author Summary
Response to foodborne disease outbreaks is complicated by globalization of our food supply chains. Rapid identification of contaminated products is essential to limit the damage caused by foodborne disease. Worldwide, foodborne disease outbreaks are responsible for $9B a year in medical costs and over $75B in economic losses. Yet relevant data required to accelerate the identification of suspicious food already exists as part of the inventory control systems used by retailers and distributors today. Combining this retail data with public health case reports has the potential to hasten outbreak investigations and provide public health investigators with better information on suspected products to test. This paper demonstrates the feasibility of the principle and efficiency of this approach. Based on these findings it can be concluded that in foodborne disease outbreaks retail data could be used to speed and target public health investigations and consequently reduce numbers of sick/dead people as well as reduce economic losses to the industry.
PMCID: PMC4080998  PMID: 24992565
11.  Prevention of foodborne listeriosis 
Listeria monocytogenes is a Gram-positive, rod-shaped bacterium which, although recognized in the medical literature as an opportunistic pathogen for the past 60 years, has only recently gained prominence as an important foodborne pathogen. Factors which make this organism unique among foodborne pathogens include its ability both to survive in foods under a variety of adverse conditions and to grow at low refrigeration temperatures. The organism is very widespread in the environment and can be found in a wide variety of foods. At least four major outbreaks definitively linked to the consumption of food containing L monocytogenes have occurred. In addition there have been a number of recent sporadic cases of listeriosis linked to the consumption of meat, fish and dairy products. The primary concern of the Health Protection Branch is contaminated foods in which L monocytogenes can grow well, and which would not normally be heated prior to consumption. Worldwide, the disease appears to be increasing in incidence, but definite links to foods are difficult to make. In most cases, individuals who come down with listeriosis include the immunocompromised, the elderly (older than 65 years) and pregnant women and their fetuses. Primary manifestations of the disease include meningitis, spontaneous abortion and septicemia. Mortality rates in foodborne listeriosis outbreaks are approximately 30%. Diagnosis of listeriosis usually requires isolation of the organism from sterile sites such as blood, cerebrospinal fluid, placenta and meconium and gastric aspirates from neonates. The recommended drug of choice is high dose intravenous ampicillin. Advice to physicians concerning measures to prevent foodborne listeriosis in high risk groups is reviewed. Included among these recommendations is avoidance of consumption of potentially hazardous foods such as soft cheese and raw products of animal origin.
PMCID: PMC3328001  PMID: 22529720
Foodborne; Listeria monocytogenes; Listeriosis; Prevention
12.  Characterization of LysB4, an endolysin from the Bacillus cereus-infecting bacteriophage B4 
BMC Microbiology  2012;12:33.
Bacillus cereus is a foodborne pathogen that causes emetic or diarrheal types of food poisoning. The incidence of B. cereus food poisoning has been gradually increasing over the past few years, therefore, biocontrol agents effective against B. cereus need to be developed. Endolysins are phage-encoded bacterial peptidoglycan hydrolases and have received considerable attention as promising antibacterial agents.
The endolysin from B. cereus phage B4, designated LysB4, was identified and characterized. In silico analysis revealed that this endolysin had the VanY domain at the N terminus as the catalytic domain, and the SH3_5 domain at the C terminus that appears to be the cell wall binding domain. Biochemical characterization of LysB4 enzymatic activity showed that it had optimal peptidoglycan hydrolase activity at pH 8.0-10.0 and 50°C. The lytic activity was dependent on divalent metal ions, especially Zn2+. The antimicrobial spectrum was relatively broad because LysB4 lysed Gram-positive bacteria such as B. cereus, Bacillus subtilis and Listeria monocytogenes and some Gram-negative bacteria when treated with EDTA. LC-MS analysis of the cell wall cleavage products showed that LysB4 was an L-alanoyl-D-glutamate endopeptidase, making LysB4 the first characterized endopeptidase of this type to target B. cereus.
LysB4 is believed to be the first reported L-alanoyl-D-glutamate endopeptidase from B. cereus-infecting bacteriophages. The properties of LysB4 showed that this endolysin has strong lytic activity against a broad range of pathogenic bacteria, which makes LysB4 a good candidate as a biocontrol agent against B. cereus and other pathogenic bacteria.
PMCID: PMC3315420  PMID: 22416675
13.  Cilantro microbiome before and after nonselective pre-enrichment for Salmonella using 16S rRNA and metagenomic sequencing 
BMC Microbiology  2015;15:160.
Salmonella enterica is a common cause of foodborne gastroenteritis in the United States and is associated with outbreaks in fresh produce such as cilantro. Salmonella culture-based detection methods are complex and time consuming, and improvments to increase detection sensitivity will benefit consumers. In this study, we used 16S rRNA sequencing to determine the microbiome of cilantro. We also investigated changes to the microbial community prior to and after a 24-hour nonselective pre-enrichment culture step commonly used by laboratory analysts to resuscitate microorganisms in foods suspected of contamination with pathogens. Cilantro samples were processed for Salmonella detection according to the method in the United States Food and Drug Administration Bacteriological Analytical Manual. Genomic DNA was extracted from culture supernatants prior to and after a 24-hour nonselective pre-enrichment step and 454 pyrosequencing was performed on 16S rRNA amplicon libraries. A database of Enterobacteriaceae 16S rRNA sequences was created, and used to screen the libraries for Salmonella, as some samples were known to be culture positive. Additionally, culture positive cilantro samples were examined for the presence of Salmonella using shotgun metagenomics on the Illumina MiSeq.
Time zero uncultured samples had an abundance of Proteobacteria while the 24-hour enriched samples were composed mostly of Gram-positive Firmicutes. Shotgun metagenomic sequencing of Salmonella culture positive cilantro samples revealed variable degrees of Salmonella contamination among the sequenced samples.
Our cilantro study demonstrates the use of high-throughput sequencing to reveal the microbiome of cilantro, and how the microbiome changes during the culture-based protocols employed by food safety laboratories to detect foodborne pathogens. Finding that culturing the cilantro shifts the microbiome to a predominance of Firmicutes suggests that changing our culture-based methods will improve detection sensitivity for foodborne enteric pathogens.
Electronic supplementary material
The online version of this article (doi:10.1186/s12866-015-0497-2) contains supplementary material, which is available to authorized users.
PMCID: PMC4534111  PMID: 26264042
14.  A review of outbreaks of foodborne disease associated with passenger ships: evidence for risk management. 
Public Health Reports  2004;119(4):427-434.
OBJECTIVE: Foodborne disease outbreaks on ships are of concern because of their potentially serious health consequences for passengers and crew and high costs to the industry. The authors conducted a review of outbreaks of foodborne diseases associated with passenger ships in the framework of a World Health Organization project on setting guidelines for ship sanitation. METHODS: The authors reviewed data on 50 outbreaks of foodborne disease associated with passenger ships. For each outbreak, data on pathogens/toxins, type of ship, factors contributing to outbreaks, mortality and morbidity, and food vehicles were collected. RESULTS: The findings of this review show that the majority of reported outbreaks were associated with cruise ships and that almost 10,000 people were affected. Salmonella spp were most frequently associated with outbreaks. Foodborne outbreaks due to enterotoxigenic E. coli spp, Shigella spp, noroviruses (formally called Norwalk-like viruses), Vibrio spp, Staphylococcus aureus, Clostridium perfringens, Cyclospora sp, and Trichinella sp also occurred on ships. Factors associated with the outbreaks reviewed include inadequate temperature control, infected food handlers, contaminated raw ingredients, cross-contamination, inadequate heat treatment, and onshore excursions. Seafood was the most common food vehicle implicated in outbreaks. CONCLUSIONS: Many ship-associated outbreaks could have been prevented if measures had been taken to ensure adequate temperature control, avoidance of cross-contamination, reliable food sources, adequate heat treatment, and exclusion of infected food handlers from work.
PMCID: PMC1497653  PMID: 15219800
15.  Assessment of the microbiological quality of fresh produce on sale in Sicily, Italy: preliminary results 
Fresh produce occupies an increasingly important place in the human food supply because of its health-promoting nutritional properties. Most fresh produce is eaten raw or after minimal processing and, consequently, pathogen contamination can represent a serious health risk. There has been an increase in foodborne outbreaks and cases associated with fresh produce, but literature data about the prevalence of pathogen contamination are inconsistent. This study was undertaken to assess the hygienic quality and the prevalence of the most common bacterial pathogens in fresh produce sold in retail markets in Sicily. A total of 125 samples of different types of vegetables were examined by standardized microbiological methods.
The aerobic mesophilic count ranged between 2 log and 7 log cfu g−1 and the Enterobacteriaceae counts between < 1 log and 6 log cfu g−1, with statistically significant differences between unprocessed and minimally processed products (p < 0.05). Escherichia coli was detected only in leaf vegetables at a concentration of 2 log - 3 log cfu g−1. Enterococci were found at a concentration of 2 log - 4 log cfu g−1. Coagulase positive Staphylococci and sulphite-reducing Clostridia were not detected in any sample. Three samples tested positive for Listeria monocytogenes, Yersinia enterocolitica and Salmonella veneziana.
Our study provides updated data on the microbiological quality of retail vegetables and confirms the need to implement strategies to increase microbial safety of fresh produce.
PMCID: PMC4389663  PMID: 25984508
Fresh produce; Vegetables; Food safety; Hygiene quality; Foodborne pathogens
16.  Antibacterial Effect of Silver Nanoparticles Against Four Foodborne Pathogens 
There is increased demand for improved disinfection methods due to microorganisms resistant to multiple antimicrobial agents. Numerous types of disinfectants are available with different properties; but the proper disinfectant must be carefully selected for any specific application to obtain the desired antimicrobial effect.
Antimicrobial effect of a commercial nanosilver product, NanoCid® L2000, against some foodborne pathogens was evaluated.
Materials and Methods:
Minimum inhibitory concentrations (MIC) were determined by monitoring the growth of bacteria at 600 nm, after 24 hours incubation at 35°C. Minimum bactericidal concentrations (MBC) were determined based on 3 log decrease in the viable population of the pathogens after incubation of nutrient agar plates at 35°C for 24 hours. The required exposure time for 3 log reduction in the viable population of the tested pathogens was determined as the minimum exposure time for efficient bactericidal activity.
The MIC values of Ag NPs against tested pathogens were in the range of 3.12-6.25 µg/mL. While Listeria monocytogenes showed the MIC value of 6.25 µg/mL, Escherichia coli O157:H7, Salmonella typhimurium and Vibrio parahaemolyticus all showed the MIC values of 3.12 µg/mL. However, all the pathogens showed the same MBC value of 6.25 µg/mL. To obtain an efficient bactericidal activity against E. coli O157:H7 and S. typhimurium, the exposure time should be at least ca. 6 hours., while this time was ca. 5 hours for V. parahaemolyticus and ca. 7 hours for L. monocytogenes.
Silver nanoparticles showed great antibacterial effectiveness on four important foodborne pathogens. Therefore, Ag NPs could be a good alternative for cleaning and disinfection of equipment and surfaces in food-related environments.
PMCID: PMC4138668  PMID: 25147658
Silver; Nanoparticles; Pathogen; Disinfection; Microbial Sensitivity Tests
17.  Endemic bacteriophages: a cautionary tale for evaluation of bacteriophage therapy and other interventions for infection control in animals 
Virology Journal  2012;9:207.
One of the most effective targets for control of zoonotic foodborne pathogens in the farm to fork continuum is their elimination in food animals destined for market. Phage therapy for Escherichia coli O157:H7 in ruminants, the main animal reservoir of this pathogen, is a popular research topic. Since phages active against this pathogen may be endemic in host animals and their environment, they may emerge during trials of phage therapy or other interventions, rendering interpretation of trials problematic.
During separate phage therapy trials, sheep and cattle inoculated with 109 to 1010 CFU of E. coli O157:H7 soon began shedding phages dissimilar in plaque morphology to the administered therapeutic phages. None of the former was previously identified in the animals or in their environment. The dissimilar “rogue” phage was isolated and characterized by host range, ultrastructure, and genomic and proteomic analyses.
The “rogue” phage (Phage vB_EcoS_Rogue1) is distinctly different from the administered therapeutic Myoviridae phages, being a member of the Siphoviridae (head: 53 nm; striated tail: 152 x 8 nm). It has a 45.8 kb genome which is most closely related to coliphage JK06, a member of the “T1-like viruses” isolated in Israel. Detailed bioinformatic analysis reveals that the tail of these phages is related to the tail genes of coliphage lambda. The presence of “rogue” phages resulting from natural enrichments can pose problems in the interpretation of phage therapeutic studies. Similarly, evaluation of any interventions for foodborne or other bacterial pathogens in animals may be compromised unless tests for such phages are included to identify their presence and potential impact.
PMCID: PMC3496638  PMID: 22985539
Escherichia coli O157:H7, VTEC; Phage therapy; Phage ecology; Genome; Proteome; Bioinformatics; Morphology; Electron microscopy
18.  Investigation of Listeria, Salmonella, and Toxigenic Escherichia coli in Various Pet Foods 
Foodborne Pathogens and Disease  2014;11(9):706-709.
The Veterinary Laboratory Investigation and Response Network (Vet-LIRN), in collaboration with the Food Emergency Response Network (FERN) and its Microbiology Cooperative Agreement Program (MCAP) laboratories, conducted a study to evaluate the prevalence of selected microbial organisms in various types of pet foods. The goal of this blinded study was to help the Center for Veterinary Medicine prioritize potential future pet food–testing efforts. The study also increased the FERN laboratories' screening capabilities for foodborne pathogens in animal feed matrices, since such pathogens may also be a significant health risk to consumers who come into contact with pet foods. Six U.S. Food and Drug Administration FERN MCAP laboratories analyzed approximately 1056 samples over 2 years. Laboratories tested for Salmonella, Listeria, Escherichia coli O157:H7 enterohemorrhagic E. coli, and Shiga toxin–producing strains of E. coli (STEC). Dry and semimoist dog and cat foods purchased from local stores were tested during Phase 1. Raw dog and cat foods, exotic animal feed, and jerky-type treats purchased through the Internet were tested in Phase 2. Of the 480 dry and semimoist samples, only 2 tested positive: 1 for Salmonella and 1 for Listeria greyii. However, of the 576 samples analyzed during Phase 2, 66 samples were positive for Listeria (32 of those were Listeria monocytogenes) and 15 samples positive for Salmonella. These pathogens were isolated from raw foods and jerky-type treats, not the exotic animal dry feeds. This study showed that raw pet foods may harbor food safety pathogens, such as Listeria monocytogenes and Salmonella. Consumers should handle these products carefully, being mindful of the potential risks to human and animal health.
PMCID: PMC4152787  PMID: 24824368
19.  Cyclic di-GMP-dependent Signaling Pathways in the Pathogenic Firmicute Listeria monocytogenes 
PLoS Pathogens  2014;10(8):e1004301.
We characterized key components and major targets of the c-di-GMP signaling pathways in the foodborne pathogen Listeria monocytogenes, identified a new c-di-GMP-inducible exopolysaccharide responsible for motility inhibition, cell aggregation, and enhanced tolerance to disinfectants and desiccation, and provided first insights into the role of c-di-GMP signaling in listerial virulence. Genome-wide genetic and biochemical analyses of c-di-GMP signaling pathways revealed that L. monocytogenes has three GGDEF domain proteins, DgcA (Lmo1911), DgcB (Lmo1912) and DgcC (Lmo2174), that possess diguanylate cyclase activity, and three EAL domain proteins, PdeB (Lmo0131), PdeC (Lmo1914) and PdeD (Lmo0111), that possess c-di-GMP phosphodiesterase activity. Deletion of all phosphodiesterase genes (ΔpdeB/C/D) or expression of a heterologous diguanylate cyclase stimulated production of a previously unknown exopolysaccharide. The synthesis of this exopolysaccharide was attributed to the pssA-E (lmo0527-0531) gene cluster. The last gene of the cluster encodes the fourth listerial GGDEF domain protein, PssE, that functions as an I-site c-di-GMP receptor essential for exopolysaccharide synthesis. The c-di-GMP-inducible exopolysaccharide causes cell aggregation in minimal medium and impairs bacterial migration in semi-solid agar, however, it does not promote biofilm formation on abiotic surfaces. The exopolysaccharide also greatly enhances bacterial tolerance to commonly used disinfectants as well as desiccation, which may contribute to survival of L. monocytogenes on contaminated food products and in food-processing facilities. The exopolysaccharide and another, as yet unknown c-di-GMP-dependent target, drastically decrease listerial invasiveness in enterocytes in vitro, and lower pathogen load in the liver and gallbladder of mice infected via an oral route, which suggests that elevated c-di-GMP levels play an overall negative role in listerial virulence.
Author Summary
Listeria monocytogenes is ubiquitously present in the environment, highly adaptable and tolerant to various stresses. L. monocytogenes is also a foodborne pathogen associated with the largest foodborne outbreaks in recent US history. Signaling pathways involving the second messenger c-di-GMP play important roles in increased stress survival of proteobacteria and mycobacteria, yet roles of c-di-GMP signaling pathways in L. monocytogenes have remained unexplored. Here, we identified and systematically characterized functions of the proteins involved in c-di-GMP synthesis, degradation and sensing. We show that elevated c-di-GMP levels in L. monocytogenes result in synthesis of a previously unknown exopolysaccharide that promotes cell aggregation, inhibits motility in semi-solid media, and importantly, enhances bacterial tolerance to commonly used disinfectants as well as desiccation. These properties of the exopolysaccharide may increase listerial survival in food processing plants as well as on produce during transportation and storage. Elevated c-di-GMP levels also grossly diminish listerial invasiveness in enterocytes in vitro, and impair bacterial accumulation in selected mouse organs during oral infection.
PMCID: PMC4125290  PMID: 25101646
20.  Application of bacteriophages for detection of foodborne pathogens 
Bacteriophage  2014;4:e28137.
Bacterial contamination of food products presents a challenge for the food industry and poses a high risk for the consumer. Despite increasing awareness and improved hygiene measures, foodborne pathogens remain a threat for public health, and novel methods for detection of these organisms are needed. Bacteriophages represent ideal tools for diagnostic assays because of their high target cell specificity, inherent signal-amplifying properties, easy and inexpensive production, and robustness. Every stage of the phage lytic multiplication cycle, from the initial recognition of the host cell to the final lysis event, may be harnessed in several ways for the purpose of bacterial detection. Besides intact phage particles, phage-derived affinity molecules such as cell wall binding domains and receptor binding proteins can serve for this purpose. This review provides an overview of existing phage-based technologies for detection of foodborne pathogens, and highlights the most recent developments in this field, with particular emphasis on phage-based biosensors.
PMCID: PMC3919822  PMID: 24533229
foodborne pathogens; bacterial detection; diagnostics; reporter phage; biosensor; phage amplification; cell wall binding domain; receptor binding protein
21.  Virulent Bacteriophage for Efficient Biocontrol of Listeria monocytogenes in Ready-To-Eat Foods▿  
Food-borne Listeria monocytogenes is a serious threat to human health, and new strategies to combat this opportunistic pathogen in foods are needed. Bacteriophages are natural enemies of bacteria and are suitable candidates for the environmentally friendly biocontrol of these pathogens. In a comprehensive set of experiments, we have evaluated the virulent, broad-host-range phages A511 and P100 for control of L. monocytogenes strains Scott A (serovar 4b) and WSLC 1001 (serovar 1/2a) in different ready-to-eat (RTE) foods known to frequently carry the pathogen. Food samples were spiked with bacteria (1 × 103 CFU/g), phage added thereafter (3 × 106 to 3 × 108 PFU/g), and samples stored at 6°C for 6 days. In liquid foods, such as chocolate milk and mozzarella cheese brine, bacterial counts rapidly dropped below the level of direct detection. On solid foods (hot dogs, sliced turkey meat, smoked salmon, seafood, sliced cabbage, and lettuce leaves), phages could reduce bacterial counts by up to 5 log units. Variation of the experimental conditions (extended storage over 13 days or storage at 20°C) yielded similar results. In general, the application of more phage particles (3 × 108 PFU/g) was more effective than lower doses. The added phages retained most of their infectivity during storage in foods of animal origin, whereas plant material caused inactivation by more than 1 log10. In conclusion, our data demonstrate that virulent broad-host-range phages, such as A511 and P100, can be very effective for specific biocontrol of L. monocytogenes in contamination-sensitive RTE foods.
PMCID: PMC2612219  PMID: 19011076
22.  The Role, Challenges, and Support of PulseNet Laboratories in Detecting Foodborne Disease Outbreaks 
Public Health Reports  2010;125(Suppl 2):57-62.
In recent years, there have been several high-profile nationwide foodborne outbreaks due to enteric organisms in food products, including Salmonella Typhimurium in peanut products, Salmonella Saintpaul in peppers, and Escherichia coli O157:H7 in spinach. PulseNet, the national molecular subtyping network for foodborne disease surveillance, played a key role in detecting each of these outbreaks.
PulseNet laboratories use bacterial subtyping methods to rapidly detect clusters of foodborne disease, which are often the first indication that an outbreak is occurring. Rapid outbreak detection reduces ongoing transmission through product recalls, restaurant closures, and other mechanisms. By greatly increasing the sensitivity of outbreak detection, PulseNet allows us to identify and correct problems with our food production and distribution systems that would not otherwise have come to our attention. Annually, millions of potentially preventable cases of foodborne illness result in billions of dollars in lost productivity and health-care expenses. We describe the critical role PulseNet laboratories play in the detection of foodborne outbreaks and discuss current challenges and potential improvements for PulseNet laboratories to more rapidly identify future foodborne outbreaks.
PMCID: PMC2846803  PMID: 20518445
23.  Foodborne Illness, Australia, Circa 2000 and Circa 2010 
Emerging Infectious Diseases  2014;20(11):1857-1864.
Overall incidence of foodborne gastroenteritis declined but remains high, and the incidence of salmonellosis and campylobacteriosis increased.
Foodborne disease is a major public health problem worldwide. To examine changes in foodborne illness in Australia, we estimated the incidence, hospitalizations, and deaths attributed to contaminated food circa 2010 and recalculated estimates from circa 2000. Approximately 25% of gastroenteritis cases were caused by contaminated food; to account for uncertainty we used simulation techniques to estimate 90% credible intervals. We estimate that circa 2010, 4.1 million foodborne gastroenteritis cases occurred, and circa 2000, 4.3 million cases occurred. Circa 2010, contaminated food was estimated to be responsible for 30,840 gastroenteritis-associated hospitalizations, 76 associated deaths, and 5,140 nongastrointestinal illnesses. Cases of salmonellosis and campylobacteriosis increased from 2000 to 2010 and were the leading causes of gastroenteritis-associated hospitalizations; Listeria monocytogenes and nontyphoidal Salmonella spp. infections were the leading causes of death. Although the overall incidence of foodborne illnesses declined over time in Australia, cases of foodborne gastroenteritis are still common.
PMCID: PMC4214288  PMID: 25340705
foodborne illness; foodborne disease; gastroenteritis; epidemiology; estimate; incidence; hospitalization; death; norovirus; salmonella; campylobacter; toxin; bacteria; parasites; viruses; Australia
24.  Contemporary issues: diseases with a food vector. 
Clinical Microbiology Reviews  1988;1(4):377-398.
Foodborne disease has become a contemporary issue. Several large, well-publicized outbreaks of foodborne disease have heightened public awareness that harmful microorganisms may be present in food and that chronic as well as acute disease may be caused by foodborne microbes. The field of food microbiology has likewise experienced a resurgence of interest. New tools, such as recombinant deoxyribonucleic acid technology and monoclonal antibody production, used to elucidate microbial virulence factors have facilitated identification of disease-causing microbes once thought to be harmless and demonstrated the complexity of individual virulence mechanisms previously considered to be well understood. Foodborne pathogens are also causing disease via some surprising food vectors, such as chopped, bottled garlic and sauteed onions. In addition to acute gastrointestinal disturbances, certain microorganisms may, through complex interactions with the human immune response, cause chronic diseases that affect several major organ systems. These microbes are serving as models in studies of molecular mimicry and genetic interrelatedness of procaryotes and eucaryotes. Other recently recognized attributes of foodborne microorganisms, such as the heat shock phenomenon and the possible nonculturability of some bacteria, may affect their ability to cause disease in humans. Because foodborne disease is a major cause of morbidity and mortality, the study of these diseases and their causative microorganisms presents a unique challenge to many professionals in the subdisciplines of microbiology, epidemiology, and clinical medicine.
PMCID: PMC358061  PMID: 3069199
25.  Food Safety in Home Kitchens: A Synthesis of the Literature 
Although foodborne illness is preventable, more than 56,000 people per year become ill in the U.S., creating high economic costs, loss of productivity and reduced quality of life for many. Experts agree that the home is the primary location where foodborne outbreaks occur; however, many consumers do not believe the home to be a risky place. Health care professionals need to be aware of consumers’ food safety attitudes and behaviors in the home and deliver tailored food safety interventions that are theory-based. Thus, the purpose of this paper is to synthesize/summarize the food safety literature by examining the following: consumers’ perceptions and attitudes towards food safety and their susceptibility to foodborne illness in the home, work, and school; common risky food safety practices and barriers to handling food safely; and the application of theory-based food safety interventions. Findings will help healthcare professionals become more aware of consumers’ food safety attitudes and behaviors and serve to inform future food safety interventions.
PMCID: PMC3799528  PMID: 24002725
food safety; food handling; foodborne illness; consumers; risky

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