Abstract
Traditional microbiological methods for testing foods for the presence of pathogens rely on growth in culture media, followed by isolation, and biochemical and serological identification. Traditional methods are laborious and time consuming, requiring a few days to a week or longer to complete. Rapid detection of pathogens in food is essential for ensuring the safety of food for consumers, and in the past 25 years, advances in biotechnology have resulted in the development of rapid methods that reduce the analysis time. Two major categories of rapid methods include immunologic or antibody-based assays and genetic-based assays such as the polymerase chain reaction. Next generation assays under development include biosensors and DNA chips that potentially have the capability for near real-time and on-line monitoring for multiple pathogens in foods. In addition to the identification and classification of microorganisms associated with foods or the food chain, global analysis methods are becoming increasingly available for analyzing these microorganisms and their environments in ways that will lead to a more complete understanding of how these organisms respond to their environments. The use of global analyses offers the opportunity to identify cellular genes, proteins, metabolites, and their interconnected networks without the need for a complete understanding of the organism prior to testing. These types of analyses have the potential to improve public health by providing the information needed to determine what causes particular organisms to become pathogenic and what causes organisms to persist in environments related to foods. This information will also allow more specific detection tests to be developed, will provide the information needed to enhance current interventions, and may possibly lead to the design and validation of new interventions.
Abstract
In the field of medical microbiology, pathogens that transmit through food are not well studied. The importance of foodborne pathogens was not realized until the 1980's when several outbreaks caused by Listeria monocytogenes and Escherichia coli O157:H7 resulted in a large number of fatalities. Since then, in-depth molecular studies have been undertaken to understand the mechanism of pathogenesis and immunity using animal and cell culture models. Several models already exist and efforts continue to find suitable ones that address unique pathogenic feature or ultimately could be used for identification and detection purposes. A specific model may be sensitive to a pathogen or a group of pathogens but may be unresponsive to others. Some pathogens are host-specific and the degree of virulence response in one model may be different from that of another. In view of this, a general description of animal and cell culture models is presented. In addition, how animal and cell culture models facilitated our understanding of selected foodborne pathogens like Listeria monocytogenes, Salmonella species, Campylobacter species, diarrheagenic Escherichia coli, Bacillus cereus, Clostridium perfringens, and Shigella species are described.
Abstract
The sensitive, rapid, and specific detection of microorganisms and toxins that taint the food supply has become increasingly important as large-scale manufacture with wide distribution can threaten large populations when a contamination occurs. Biosensors have been seen as a means to provide a higher level of surveillance in a more automated and rapid manner. Only in the last few years have biosensors matured to the point where they can begin to meet these demanding applications. In this review we will endeavor to touch upon several biosensor methodologies and give the reader some insight as to what technologies are available and how they might be applied for their particular detection needs. There are, however, numerous detection technologies, with more being developed constantly. Regrettably therefore, not all methods will be covered, but we do hope to present of representative cross-section of techniques.
Abstract
Molecular typing of foodborne pathogens is used to generate approximations of population variation, definition of specific clonal lineages, comparison of isolates of similar species from different geographical locations, and changes of types within the population over time. Thus, it can be used to confirm the identity of organisms responsible for sporadic cases or foodborne outbreaks, as well as facilitating trace-back investigations and food product recalls. Validation of typing methods should include tests for intra- and inter-laboratory reproducibility for sets of known and test strains to ensure that appropriate standardization of methodology can be achieved. Typeability, the proportion of the population of micro-organisms that can be typed, and discriminatory power, the ability to distinguish unrelated strains, are two important endpoints when developing a molecular characterization scheme. The utility of any typing or subtyping method depends in part on the size and extent of the database with which any new isolate can be compared. It has become widely accepted that no single typing or fingerprinting method will be completely accurate or informative, and that a combination of methods must often be used. The output from these methods, however, cannot be looked at in isolation, and should be combined with epidemiological data when investigating foodborne illnesses. The following chapter describes some of the current phenotypic (serology, phage typing), genotypic (PFGE, RAPD, ribotyping) and emerging (Maldi-Tof mass spectroscopy, AFLP, MLST, VNTR, Microarray technology) methods used to characterize bacterial foodborne pathogens.
Abstract
Bacteria can be subjected to chemical, physical and biological stresses in the environment, in foods and food preparation/production processes and in the body, and several such stresses influence survival in foods. Stress exposure can lead to damage at several cellular sites, but for most stresses, damage to DNA, to membranes and to enzymes is most significant for lethality. Ability to survive stress challenges not only depends on inherent tolerance, but also on the extent to which tolerance responses are induced. Many of these responses involve tolerance specifically to the inducing stress, but cross-tolerance responses occur, as does cross-sensitisation. Here, regulation of such processes is considered, with the conclusion that rapid induction of responses and early warning against impending stress exposures, depends on the functioning of extracellular sensing components (ESCs) and extracellular induction components (EICs). The pheromonal/alarmonal intercellular communication afforded by these agents may aid survival of contaminating organisms in foods, allowing such organisms to go on to cause disease on ingestion. A range of biochemical changes occur following switching-on of responses, and the structure, properties and functioning of heat-shock proteins are emphasized here, as are those changes that lead to thermotolerance, acid tolerance and irradiation tolerance.
Abstract
Cells in the viable but nonculturable (VBNC) state are alive, but undetectable by routine microbiological methods. The presence of such cells in foods presents a special concern, especially when they are human pathogens. This chapter reviews the biology of the VBNC state and the factors which induce it, the foodborne pathogens that are known to enter this state, how cells resuscitate back to the actively growing state, and the importance of the VBNC state in food microbiology.
Abstract
Accurately predicting the fate of microbial pathogens in food is a goal of all concerned food safety specialists employed by food companies, government agencies, academic institutions and consulting firms. In this regard, predictive microbiology has emerged as an important scientific discipline for estimating the consequences of diverse food handling and processing operations on the growth, survival and inactivation of microbial pathogens. The development and successful implementation of predictive models involves a series of steps that include high quality experimental designs, sound mathematical algorithms, valid models and effective user interfaces. The net results are tools that are used in HACCP plans to define critical control points and critical limits, as well as safe remedial actions when deviations occur. This chapter provides an overview of current concepts in the field of predictive microbiology and how this discipline can contribute to the production of safer foods, international commerce and increased consumer confidence.
Abstract
Food- and waterborne viruses contribute to a substantial number of illnesses throughout the world. Among those most commonly known are hepatitis A virus, rotavirus, astrovirus, enteric adenovirus, hepatitis E virus, and the human caliciviruses consisting of the noroviruses and the Sapporo viruses. This diverse group has something in common: they are transmitted by the fecal-oral route, often by ingestion of contaminated food and water. This chapter provides an introduction to the enteric viruses including the diseases they cause, their characteristics, mechanisms of pathogenesis, inactivation procedures, and methods for their detection, analysis, and control.
Abstract
Protozoan parasites have been associated with food and waterborne outbreaks causing illness in humans. Although parasites are more commonly found in developing countries, developed countries have also experienced several foodborne outbreaks. Contaminants may be inadvertently introduced to the foods by inadequate handling practices, either on the farm or during processing of ready-to-eat foods. In some instances, this contamination occurred in endemic regions and is carried to non-endemic areas where an outbreak is initiated. Other protozoan parasites can be found worldwide, either infecting wild animals or in an environment such as water and eventually finding its way to crops grown for human consumption. Parasites can infect immunocompetent individuals, however the clinical presentation can be much more severe and prolonged in immunocompromissed individuals.
Abstract
Molds produce mycotoxins, which are secondary metabolites that can cause acute or chronic diseases in humans when ingested from contaminated foods. Although the mechanisms and health effects of most mycotoxins are not completely resolved, potential diseases include cancers and tumors in different target organs (heart, liver, kidney, nerves), gastrointestinal disturbances, alteration of the immune system, and reproductive problems. Species of Aspergillus, Fusarium, Penicillium, and Claviceps grow in agricultural commodities or foods and elaborate the major mycotoxins, namely aflatoxins, deoxynivalenol, ochratoxin A, fumonisins, ergot alkaloids, T-2 toxin, and zearalenone and minor mycotoxins such as cyclopiazonic acid and patulin. Mycotoxins occur mainly in cereal grains (barley, maize, rye, wheat), coffee, dairy products, fruits, nuts and spices. Control of mycotoxins in foods has focused on minimizing mycotoxin production in the field, during storage or destruction once produced; however, most control approaches have not been totally successful. Monitoring foods for mycotoxins is important to manage strategies such as regulations and guidelines, which are used by 77 countries, and for developing exposure assessments essential for accurate risk characterization. Chromatographic methods and immunoassays are most commonly used to detect mycotoxins. Research will continue to elucidate different aspects of mycotoxins and their importance to human health.
Abstract
Yersinia enterocolitica includes well-established pathogens and environmental strains that are ubiquitous in terrestrial and fresh water ecosystems. Evidence from large outbreaks of yersiniosis and from epidemiological studies of sporadic cases has shown that Y. enterocolitica is a foodborne pathogen, and that in many cases pork is implicated as the source of infection. The pig is the only animal consumed by man that regularly harbours pathogenic Y. enterocolitica. An important property of the bacterium is its ability to multiply at temperatures near to 0ƒC, and therefore in many chilled foods. The pathogenic serovars (mainly O:3, O:5,27, O:8 and O:9) show different geographical distribution. However, the appearance of strains of serovars O:3 and O:9 in Europe, Japan in the 1970s, and in North America by the end of the 1980s, is an example of a global pandemic. The possible risk of reactive arthritis following infection with Y. enterocolitica has led to further attention being paid to this microbe.
Abstract
Vibrio species are prevalent in estuarine and marine environments and seven species can cause seafoodborne infections. Vibrio cholerae O1 and O139 serovtypes produce cholera toxin and are agents of cholera. However, fecal-oral route infections in the terrestrial environment are responsible for epidemic cholera. V. cholerae non-O1/O139 strains may cause gastroenteritis through production of known toxins or unknown mechanism. Vibrio parahaemolytitucs strains capable of producing thermostable direct hemolysin (TDH) and/or TDH-related hemolysin are most important cause of gastroenteritis associated with seafood consumption. Vibrio vulnificus is responsible for seafoodborne primary septicemia and its infectivity depends primarily on the risk factors of the host. V. vulnificus infection has the highest case fatality rate (50%) of any foodborne pathogen. Four other species (Vibrio mimicus, Vibrio hollisae, Vibrio fluvialis, and Vibrio furnissii) that have potential to cause gastroenteritis have been reported. Some strains of these species produce known toxins but the pathogenic mechanism is largely not understood. The ecology of and detection and control methods for all seafoodborne Vibrio pathogens are essentially similar.
Abstract
Staphylococcus aureus is a common cause of confirmed bacterial foodborne disease worldwide. Food poisoning episodes are characterized by symptoms of vomiting and diarrhea that occur shortly after ingestion of S. aureus-contaminated food. The symptoms arise from ingestion of preformed enterotoxin, which accounts for the short incubation time. Staphylococcal enterotoxins are a family of sequence similar, but serologically distinct proteins. These proteins have the additional property of being superantigens and, as such, have adverse effects on the immune system. The enterotoxin genes are accessory genetic elements in S. aureus, meaning that not all strains of this organism are enterotoxin-producing. The enterotoxin genes are found on prophage, plasmids, and pathogenicity islands in different strains of S. aureus. Expression of the enterotoxin genes is often under the control of global virulence gene regulatory systems. Although much progress has been made recently in defining enterotoxin structure and superantigenicity properties, much remains to be learned regarding the binding of enterotoxins to receptors in the gastrointestinal tract and how toxin production leads to the symptoms associated with staphylococcal food poisoning.
Abstract
Campylobacter spp., primarily C. jejuni subsp. jejuni is one of the major causes of bacterial gastroenteritis in the U.S. and worldwide. Campylobacter infection is primarily a foodborne illness, usually without complications; however, serious sequelae such as Guillain-Barre Syndrome occur in a small subset of infected patients. Detection of C. jejuni in clinical samples is readily accomplished by culture and non-culture methods, although improvements in diagnostic approaches are needed. A significant body of knowledge exists on the epidemiology of Campylobacter infections; however, much less is known about the mechanism of disease, despite over 2 decades of research.
Abstract
Listeria monocytogenes is Gram-positive foodborne bacterial pathogen and the causative agent of human listeriosis. The organism has served as a model for the study of intracellular pathogenesis for several decades and many aspects of the pathogenic process are well understood. Listeriae are acquired primarily through the consumption of contaminated foods including soft cheese, raw milk, deli salads, and ready-to-eat foods such as luncheon meats and frankfurters. Although L. monocytogenes infection is usually limited to individuals that are immunocompromised, the high mortality rate associated with human listeriosis makes L. monocytogenes the leading cause of death amongst foodborne bacterial pathogens. As a result, tremendous effort has been made at developing methods for the isolation, detection and control of L. monocytogenes in foods. Additional research in the area of genomics and proteomics has begun to be applied toward developing a better understanding of how L. monocytogenes responds to its environment. These efforts will allow a more complete understanding of the pathogenic process and will aid the design and development of targeted strategies for detection and intervention, leading to improved control of L. monocytogenes in foods.
Abstract
Salmonella serotypes continue to be a prominent threat to food safety in the United States. Infections are commonly acquired by animal to human transmission though consumption of undercooked food products derived from livestock or domestic fowl. The second half of the 20th century saw the emergence of Salmonella serotypes that became associated with new food sources (i.e. chicken eggs) and the emergence of Salmonella serotypes with resistance against multiple antibiotics. This review provides an overview over epidemiology, pathogenesis and control of this important foodborne disease in the United States.
Abstract
Shigella species are members of the family Enterobacteriacae and are Gram negative, non-motile rods. Four subgroups exist based on O-antigen structure and biochemical properties; S. dysenteriae (subgroup A), S. flexneri (subgroup B), S. boydii (subgroup C) and S. sonnei (subgroup D). Clinical manifestations include mild to severe diarrhea with or without blood, fever, tenesmus, and abdominal pain. Further complications of the disease may be seizures, toxic megacolon, reactive arthritis and hemolytic uremic syndrome. Transmission of the pathogen is by the fecal-oral route, commonly through food and water. The infectious dose ranges from 10-100 organisms. Shigella spp. have a sophisticated pathogenic mechanism to invade colonic epithelial cells of the host, man and higher primates, and the ability to multiply intracellularly and spread from cell to adjacent cell via actin polymerization. Shigellae are one of the leading causes of bacterial foodborne illnesses and can spread quickly within a population.
Abstract
More information is available concerning Escherichia coli than any other organism, thus making E. coli the most thoroughly studied species in the microbial world. For many years, E. coli was considered a commensal of human and animal intestinal tracts with low virulence potential. Today, it is well known that many strains of E. coli act as pathogens inducing serious gastrointestinal diseases and even death in humans. There are six major categories of E. coli strains that cause enteric diseases in humans including the (1) enterohemorrhagic E. coli, which cause hemorrhagic colitis and hemolytic uremic syndrome, (2) enterotoxigenic E. coli, which induce traveler's diarrhea, (3) enteropathogenic E. coli, which cause a persistent diarrhea in children living in developing countries, (4) enteroaggregative E. coli, which provoke diarrhea in children, (5) enteroinvasive E. coli that are biochemically and genetically related to Shigella species and can induce diarrhea, and (6) diffusely adherent E. coli, which cause diarrhea and are distinguished by a characteristic type of adherence to mammalian cells. Genomic studies on the diarrhea-inducing E. coli have provided much information on the nature of the pathogenic mechanisms of these organisms and have provided information that can be used to design techniques for the detection of specific E. coli strains. In spite of extensive study, more information is needed concerning the interaction of the human host with pathogenic E. coli.
Abstract
Clostridium botulinum produces extremely potent neurotoxins that result in the severe neuroparalytic disease, botulism. Although of lower lethality, the enterotoxin produced by C. perfringens, during sporulation of vegetative cells in the host intestine, still results in debilitating acute diarrhea and abdominal pain. Sales of refrigerated, processed foods of extended durability including sous-vide foods, chilled ready-to-eat meals, and cook-chill foods have increased over recent years. As a result of conditions accommodating growth, anaerobic spore-formers have been identified as the primary microbiological concerns in these foods. Heightened awareness over intentional food source tampering with botulinum neurotoxin has arisen with respect to genes encoding the toxins that are capable of transfer to nontoxigenic clostridia. Similarly, enterotoxin produced by C. perfringens and the genomic location of the cpe gene has epidemiologic significance for understanding the capability to cause foodborne disease in humans. This chapter focuses on the unique characteristics and virulence factors of C. botulinum and C. perfringens that make them foodborne hazards in the food supply. The susceptibility of these bacterial spore-formers to physical and chemical agents is examined as well as recommended control measures. This information is useful in developing molecular strategies to study virulence genes and their regulation as a means to safer foods.
Abstract
The Bacillus cereus group comprises six members: B. anthracis, B. cereus, B. mycoides, B. pseudomycoides, B. thuringiensis and B. weihenstephanensis. These species are closely related and should be placed within one species, except for B. anthracis that possesses specific large virulence plasmids. B. cereus is a normal soil inhabitant and is frequently isolated from a variety of foods, including vegetables, dairy products and meat. It causes an emetic or a diarrhoeal type of food-associated illness that is becoming increasingly important in the industrialized world. Some patients may experience both types of illness simultaneously. The diarrhoeal type of illness is most prevalent in the western hemisphere, whereas the emetic type is most prevalent in Japan. Desserts, meat dishes, and dairy products are the foods most frequently associated with diarrhoeal illness, whereas rice and pasta are the most common vehicles of emetic illness. The emetic toxin (cereulide) has been isolated and characterized; it is a small ring peptide synthesised non-ribosomally by a peptide synthetase. Three types of B. cereus enterotoxins involved in foodborne outbreaks have been identified. Two of these enterotoxins are three-component proteins and are related, while the last is a one-component protein (CytK). Deaths have been recorded both by strains that produce the emetic toxin and by a strain producing only CytK. Some strains of the B. cereus group are able to grow at refrigeration temperatures. These variants raise concern about the safety of cooked, refrigerated foods with an extended shelf life. B. cereus spores adhere to many surfaces and survive normal washing and disinfection (except for hypochlorite and UVC) procedures. B. cereus foodborne illness is likely underreported because of its relatively mild symptoms, which are of short duration. However, consumer interest in precooked chilled food products with a long shelf life may lead to products well suited for B. cereus survival and growth. The availability of such foods could increase the prominence of B. cereus as a foodborne pathogen.
Abstract
Sabotage of foods by terrorists and criminals has occurred in the U.S., though rarely. A multiplicity of suitable biological and chemical agents exists and the vast contemporary food supply is vulnerable. Prevention requires enhancement of food security. Since an outbreak caused by food sabotage would most likely be detected and handled by the existing public health system, minimization of casualties requires a robust standing public health infrastructure capable of detecting, investigation and controlling all foodborne disease outbreaks, intentional and unintentional, and providing appropriate medical resources.
Abstract
There are a number of factors involved in the emergence or re-emergence of pathogens associated with foodborne illness in the United States and other developed countries. These include environmentally-related factors, such climate changes and deforestation, food-related factors, such as changes in food production and distribution practices, consumer-related factors, such as increased international travel and changes in eating habits, and pathogen-related factors, such as genetic changes in microorganisms as a result of exposure to environmental stresses. One major factor is the increased globalization of the food supply, resulting in transfer of pathogenic agents between countries. The use of antimicrobials for prophylaxis in animals has contributed to the emergence of bacterial strains resistant to multiple antibiotics. Potential emerging food-related diseases include hepatitis caused by the hepatitis E virus, intestinal spirochetosis caused by Brachyspira pilosicoli, gnathostomiasis caused by nematodes belonging to the genus Gnathostoma, and anisakidosis caused by fish nematodes. Other potential emerging pathogens include non-gastric Helicobacter spp., Enterobacter sakazakii, non-jejuni/coli species of Campylobacter, and non-O157 Shiga toxin-producing Escherichia coli. An increased awareness of emerging pathogens, consumer education, changes in food production and handling practices from farm to table, and improvements in microbiological detection methods will be needed to prevent the spread of emerging foodborne diseases.
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