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Category: Food Microbiology; Applied and Industrial Microbiology
Pathogens and Toxins in Foods: Challenges and Interventions offers a farm-to-table approach to food safety that enables readers to control microbial pathogens and toxic agents at all stages of the food supply chain. The book begins with chapters that help readers understand the characteristics of specific pathogens and toxins, the illnesses they cause, and the factors such as food processing operations that affect their survival and growth in food products.
Further, the chapters in the book explore the most recent advances in biological, chemical, and physical interventions to control food-borne hazards during pre-harvest, harvest, food processing, and in retail ready-to-eat foods and food service operations. Also included are chapters that discuss the latest methods to rapidly detect food-borne pathogens as well as the implementation of comprehensive food safety management systems.
Each chapter has been written by one or more leading experts in the field of food safety. Their advice is based on a thorough investigation of the literature as well as their own first-hand experience. In short, by drawing from hundreds of sources, this book offers food safety professionals a unique, single reference containing the latest understanding of food-borne hazards as well as the latest methods to detect and control their incidence.
Hardcover, 512 pages, illustrations, index.
Bacillus spp. are gram-positive, endospore-forming facultatively anaerobic bacteria. The resistance of their spores to adverse conditions has resulted in widespread distribution of the organism. The bacteria of the genus Bacillus are usually free living, that is, not host adapted, and their spores are widely distributed throughout nature. The spores of Bacillus cereus are ellipsoidal and central to subterminal and do not distend the sporangia. Early in the growth cycle vegetative cells are gram positive, but cells may become gram variable when in late log or stationary phase. Colonies on agar media have a dull or frosted appearance. Two distinct types of illness have been attributed to the consumption of foods contaminated with B. cereus: the diarrheal syndrome and the emetic syndrome. As well as causing enteric illness, B. cereus has been responsible for postoperative infections, especially in immunocompromised patients. Early experiments relying on monkey feeding trials identified the cause of the emetic syndrome as a toxin because cell-free supernatants produced the same symptoms as cell cultures. Germination of spores requires the presence of purine ribosides and glycine or a neutral l-amino acid. Fourier transform infrared spectroscopy can provide a way to differentiate bacterial genera and species through unique Fourier transform infrared vibrational combination bands produced from active components of bacterial cells. Control against food poisoning should be directed at preventing germination of spores and minimizing growth of vegetative cells.
Campylobacter species have a chemoorganotrophic metabolism, and energy is derived from amino acids or tricarboxylic acid cycle intermediates due to their inability to oxidize or ferment carbohydrates. The majority of Campylobacter spp. reduce nitrate and nitrite. Campylobacter jejuni contains two flagellin genes, flaA and flaB; the wild-type bacterium expresses flaA only, but flaB can be expressed under certain conditions. The flagellum of Campylobacter spp. plays a much more important function than just motility. C. jejuni flagella may also play a role in the dissemination and internalization of the organism. Toxin production plays a role in pathogenicity. In regard to C. jejuni, the organism synthesizes several toxins, classified mainly as enterotoxins or cytotoxins. The prevalence of Campylobacter contamination of carcasses and poultry products can vary greatly, depending on the sensitivity of the cultural procedures utilized and by the point along the process chain at which sampling is being conducted. Cross-contamination of food products is a major factor that contributes to human illness. Campylobacter spp. can be sensitive to environmental conditions outside of an animal’s intestinal tract. While outbreaks of human campylobacteriosis have been associated with raw milk and untreated water, poultry meat, which is frequently contaminated with the organism, may be responsible for as much as 70% of sporadic campylobacteriosis. This chapter focuses on recent advantages in biological, chemical, and physical interventions to guard against the pathogen, and discriminative detection methods for confirmation and trace-back of contaminated products.
The ability to form botulinum neurotoxin is restricted to strains of Clostridium botulinum and some strains of Clostridium baratii and Clostridium butyricum. Nonproteolytic C. botulinum is a psychrotroph, with growth and neurotoxin formation reported at 3.0°C but not at 2.5°C. Spores formed by nonproteolytic C. botulinum are of moderate heat resistance. The foods most commonly involved in outbreaks are fermented marine products, dried fish, and vacuum-packed fish. The genetic diversity of nonproteolytic C. botulinum strains appears greater than that of proteolytic C. botulinum strains. Food-borne botulism is a severe but rare neuroparalytic intoxication resulting from consumption of preformed botulinum neurotoxin. Food-borne botulism has also occurred when ingredients containing preformed botulinum neurotoxin have been added to a correctly refrigerated product. The natural habitat of proteolytic C. botulinum and nonproteolytic C. botulinum is soil and sediments. Proteolytic C. botulinum produces spores with high heat resistance and is the principal concern for the safe production of low-acid canned foods. This chapter describes methods for the detection of C. botulinumand its neurotoxins. Nonproteolytic C. botulinum has been identified as the principal safety hazard in minimally heated refrigerated foods, and it is essential that research continues to underpin the safe development of these novel foods. A more recent concern is the deliberate introduction of C. botulinum or its neurotoxin into the food chain through a bioterrorism act.
Clostridium perfringens is an anaerobic (microaerophilic), gram-positive, nonmotile, spore-forming, rod-shaped bacterium. C. perfringens is ubiquitous in the environment and is found in soil, dust, raw ingredients, such as spices used in food processing, and in the intestines of humans and animals. C. perfringens outbreaks usually result from improper handling and preparation of foods, such as inadequate cooling at the home, retail, or food service level, rarely involving commercial meat processors. This chapter discusses intrinsic and extrinsic factors that affect survival and growth in food products and contribute to outbreaks, and focuses on food processing operations that influence the numbers, spread, or characteristics. The presence of inhibitory agents in the products can affect germination of C. perfringens spores and may also affect the minimum growth temperatures for the germinated spores. Recent research has focused on combining traditional inactivation, survival, and growth-limiting factors at subinhibitory levels with emerging novel nonthermal intervention food preservation techniques using ionizing radiation, high hydrostatic pressure, or exposure to ozone. The ability of C. perfringens to cause food-borne illness and occasional associated outbreaks necessitates effective discriminatory detection methods for this pathogen in order to ensure reliable and confirmatory epidemiological screening of suspected foods. Many predictive growth models have been developed to accurately estimate C. perfringens survival following various types of food processing scenarios. The best strategy to control C. perfringens appears to be a hurdle approach combined with careful handling of foods to avoid temperature abuse.
This chapter presents recent advances in control measures used in food processing, as well as discriminative detection methods for confirmation of these pathogens and trace-back of contaminated food products. Common symptoms associated with human diarrheagenic E. coli infections generally include loose, watery stools (diarrhea) and mild to severe abdominal pain and/or cramping. Colonization of host gastrointestinal (GI) tissue is rather methodical, and evasion of host defenses, colonization, replication, and damage to the host are observed with all diarrheagenic E. coli infections. The toxins involved in diarrheagenic E. coli infections are also unique to each class. While many types of E. coli toxins exist, Shiga toxins (also known as Shiga-like toxins or verotoxins) are similar to those produced by Shigella dysenteriae. Animal feces are the source of contamination for animal hides, water, soil, and inanimate objects, leading to transfer of contamination to raw food ingredients, processing water, equipment, and workers. Rapid detection methods have become increasingly popular in the food industry for the detection of specific pathogens and toxins. The documentation of smaller and smaller outbreaks is indicative of successful surveillance efforts that include the refinement and standardization of laboratory techniques, improved reporting and sharing of information, and induction of more regional testing facilities which cater to a larger proportion of the national population.
In 1924 in Cambridge, England, what is now known as Listeria monocytogenes was first documented by E. G. D. Murray and colleagues (1926) as the causative agent of a septic illness, peripheral monocytosis, in laboratory rabbits. Between 1976 and 2002, there were 27 outbreaks of food-borne listeriosis reported worldwide, with about 2,900 cases and about 260 deaths (mortality rate of ca. 9.0%). L. monocytogenes is widespread in nature, being associated with plants, soil, water, sewage, feed, and animals raised as food. L. monocytogenes growth/survival at low temperatures requires maintenance of membrane fluidity for appropriate enzymatic activity and transport of solutes across the membrane, as well as for structure stabilization of macromolecules, such as ribosomes, and/ or the uptake or synthesis of compatible cryoprotectant solutes, such as glycine betaine and carnitine. Control of L. monocytogenes is one of the most difficult challenges faced by manufacturers and handlers of ready-to-eat (RTE) meat, poultry, seafood, and dairy products. Traditional milk pasteurization times/temperatures are also considered generally adequate to eliminate the typically low levels of L. monocytogenes that may be present in raw milk. The only bacteriocin that has been granted the FDA approval is nisin, which is allowed for use in low-moisture/lowsalt pasteurized processed cheese. Many organic acids have generally recognized as safe (GRAS) status as food ingredients, and studies have shown their effectiveness under various conditions and in different foodstuffs.
This chapter provides a basic understanding of the characteristics and illness, along with the sources and incidence of Salmonella in the environment and food commodities. The majority of persons infected with Salmonella develop diarrhea, fever, and abdominal cramps 12 to 72 hours after infection. The majority of Salmonella spp. are motile by peritrichous flagella. The occurrence of Salmonella in food products which are capable of harboring the organism, but traditionally not considered to harbor the organism, presents serious problems to food safety. Outside of preventing Salmonella from ever entering the breeder or grow-out farms and being an effective method for preventing Salmonella in processed broilers, the development and use of undefined competitive exclusion (CE) cultures probably have been the most effective interventions. Isolation and identification of Salmonella by traditional cultural methods requires a series of steps for isolation and identification, which takes 4 to 6 days to complete. To reduce the screening time, rapid methods (i.e., miniaturized biochemical kits, antibody/ DNA-based tests, and modifications to conventional tests) are utilized to detect the presence of Salmonella in sample. Increased understanding of Salmonella at the molecular level will possibly lead to better intervention strategies, real-time screening methods, and a dramatic reduction of Salmonella in certain food products. However, with the increase in globalization, efforts to control Salmonella will continue to be a significant issue well into the future as new products are continually introduced into the food arena.
This chapter focuses predominantly on staphylococcal food poisoning (SFP), another toxin-mediated illness. SFP, also known as staphylococcal gastroenteritis, is not an infection but is a foodborne intoxication caused by one or more staphylococcal enterotoxins (SEs). It appears to have been initially reported in 1894 as a family outbreak due to undercooked meat from a sick cow that became contaminated with Staphylococcus aureus. Staphylococci are often divided into coagulasepositive staphylococci and coagulase-negative staphylococci (CNS), on the basis of coagulase production or the presence of a coagulase gene. Staphylococcal osmotolerance is problematic for food safety since blocked growth of competing bacteria can result in a more likely overgrowth of S. aureus. Staphylococci are ubiquitous in air, dust, sewage, water, milk, and many foods and on food equipment, environmental surfaces, humans, and animals. SE production is affected by temperature, pH, and osmotic conditions and is also regulated at the molecular level. The oligonucleotideoligosaccharide- binding fold containing a β-barrel structure capped with an α-helix comprises much of one domain and is present in other toxins including cholera toxin, pertussis toxin, and Shiga toxin. Recent studies demonstrated that staphylococcal pathogenicity island (SaPI) is mobilized by staphylococcal bacteriophages and endogenous prophages, suggesting that SE genes might be transferred horizontally. The identification of novel toxins and improved methods of detection have also indicated that SE production is much more widespread than originally thought and includes species of staphylococci other than S. aureus.
Diarrheal diseases afflict a significant number of the world’s population each year. Estimates of disease caused by Shigella spp. on a yearly basis worldwide range from 164.7 to 200 million people infected, with nearly 1.1 million deaths attributed to this pathogen. Destruction of the intestinal epithelial cells and mucosal inflammation is a consequence of the host’s polymorphonuclear leukocytes and a subsequent recruitment influx of chemokines and cytokines at the sites of Shigella invasion. Shigellosis is a highly communicable disease due in part to the rapid spread of the pathogen within certain populations, particularly in crowded communities and/or in environments with poor sanitary conditions. The primary means of human-to-human transmission of Shigella is by the fecal-oral route. Most cases of shigellosis are caused by the ingestion of fecal-contaminated food or water. Surveillance of food-borne illnesses caused by Shigella spp. continues in many countries, with many reporting to a central repository at the World Health Organization. Introduction of shigellae into foods, particularly raw vegetables/produce, most likely occurs during processing, including irrigation, harvesting, and hand packaging. Food matrices have diverse effects on the ability of the pathogen to either grow or survive. Technology of today can be the basis of instruments in the near future that will result in analysis being completed in real time and being automated and portable, two assets that will definitely impact food safety and food defense.
The primary pathogens in the genus Vibrio are Vibrio parahaemolyticus, V. cholerae, and V. vulnifius. Other Vibrio species that can cause human disease include V. hollisae, V. alginolyticus, V. damsela, V. mimicus, V. fluvialis , V. metschnikovii, V. furnissii, V. cincinnatiensis, and V. carchariae, but reported cases are either relatively rare or do not involve food-borne transmission. Nonepidemic V. cholerae is also responsible for occasional seafood-borne disease in the United States and can be distinguished from epidemic disease by the severity of symptoms, the serogroups of associated strains, and the capacity for global spread. V. vulnificus is the most common cause of serious wound infections associated with Vibrio species, and these infections may result from exposure of breached skin surface to seawater or contaminated seafood handling. This chapter talks about intrinsic factors and extrinsic factors. Comparison of heat resistances for pathogenic vibrios showed that D55 values varied among species. V. parahaemolyticus (D55 of 1.75 min) was considerably more resistant compared to V. vulnificus and V. cholera. Approved and validated treatments include high hydrostatic pressure, pasteurization (heat shock), and individual quick freezing. These treatments are generally used in combination with approved transport and storage practices involving icing, refrigeration, and/or freezing. Greater understanding of the role of the bacteria in estuarine ecosystems and the risks associated with environmental, bacterial, and host factors is crucial for control and safety of seafood products.
Yersiniosis is an infectious disease caused by Yersinia, food-borne yersiniosis being due to Yersinia enterocolitica or Yersinia pseudotuberculosis. Jerret and coworkers reported that Y. pseudotuberculosis is one of the most common infectious causes of death among farmed deer in Australia. The primary transmission route of human yersiniosis is proposed to be fecal-oral via contaminated food. The most important intrinsic factors are nutrition, pH, and water activity. The most important extrinsic factors include temperature and gas atmosphere. DNA extraction procedures using silica particles or chelex resin have commonly been used, as they are rapid and simple to use; however, they are not necessarily the most effective methods to remove inhibitors from complex matrices. The majority of Y. enterocolitica isolates recovered from nonhuman sources are considered nonpathogenic; thus, it is important to assess the pathogenicity of isolates. The methods are based on specific segments of the virulence plasmid or the chromosomal DNA with known virulence functions. A combination of direct contact with wildlife feces during the storage and cross-contamination of the equipment are the most likely contributing factors. Although several studies on the epidemiology of enteropathogenic Yersinia have been conducted, a lot of questions remain to be solved using DNA-based detection and characterization methods in the future.
This chapter covers the bacterial pathogens that include: Aeromonas, Arcobacter, Helicobacter, Mycobacterium, Plesiomonas, and Streptococcus and attempts to provide a concise, thorough overview of the significance, characteristics, and food safety concerns involving each pathogen. Aeromonas species are indicated as important human pathogens causing gastrointestinal and other infections in healthy and immunocompromised hosts. “Aerolysins” are toxins produced by some Aeromonas species that have hemolytic, enterotoxic, and cytolytic activity. The importance of aeromonads as pathogens of food-borne origin dates back to the 1950s, following their isolation from humans. Campylobacter spp. have been identified as the leading cause of bacterial food-borne diarrheal illness in humans. The genus Helicobacter was created in 1989 and includes about 23 recognized species. Transmission of Helicobacter pylori through foods leading to incidences of food-borne illness has been speculated but not demonstrated to date. In both humans and animals, Mycobacterium avium subsp. paratuberculosis is thought to exist in protoplast form, which makes identification by acid-fast staining (Ziehl-Neelsen method) untenable. Plesiomonas shigelloides produces a heat-stable enterotoxin, but based on a lack of consistent in vitro and in vivo evidence, the species is thought to possess low pathogenicity. Earlier in the 20th century, there were efforts to reduce the incidence of food-borne illness due to Streptococcus species. While there are still occasional cases of illness reported, the intervention methods put in place have greatly reduced the likelihood of food-borne illness due to members of this genus.
Food-borne infections are a significant cause of morbidity and mortality worldwide, and food-borne parasitic diseases, though not as widespread as bacterial and viral infections, are common on all continents and in most ecosystems, including arctic, temperate, and tropical regions. Major food-borne trematodiasis in humans has been discussed in this chapter. Taenia saginata, the beef tapeworm, and T. asiatica and T. solium, the pork tapeworms, cause taeniasis in humans. Taenia saginata and T. solium occur worldwide, endemically in underdeveloped regions where pork and beef are consumed and sporadically in developed nations, largely due to importation by immigrants and travelers. The neck of the tapeworm begins the process of strobilation, the production of proglottids. Humans and other piscivorous mammalian hosts harbor the adult tapeworm, which is attached to the small intestinal surface by the scoop-shaped scolex and bothria (or grooves), which are characteristic holdfast organs of pseudophyllidean tapeworms. Adult tapeworms are generally benign, but abdominal pain, nausea, and diarrhea may occur, and Diphyllobothrium latum may absorb enough vitamin B12 to cause deficiency in malnourished individuals. Nematodes in the genus Trichinella are some of the most commonly recognized agents of food-borne parasitic disease. Gnathostomes are species belonging to a geographically widespread genus but are most commonly found as adult worms in carnivorous mammals in Asia. The most widespread protozoan parasite affecting humans is Toxoplasma gondii. To prevent food-borne infection by T. gondii, the hands of people handling meat should be washed thoroughly with soap and water before they go to other tasks.
This chapter focuses primarily on those viruses for which food-borne transmission is well documented (hepatitis A virus (HAV) and noroviruses (NoV)), and therefore, control in food production, processing, and preparation is considered relevant. General information about structural, molecular, and environmental properties of those viruses specifically implicated in food-borne illness is detailed. Three types of food commodities are usually associated with viral disease outbreaks, those being (i) molluscan shellfish contaminated during production; (ii) fresh produce items contaminated during production, harvesting, or packing; and (iii) prepared foods contaminated during preparation. Poor personal hygiene practices of infected food handlers provide the source of contamination for prepared foods. This appears to be the most important factor influencing the food-borne transmission of enteric viruses, as U.S. Centers for Disease Control and Prevention (CDC) data indicate that 50 to 95% of viral food-borne disease outbreaks are attributable to poor personal hygiene of infected food handlers. In Europe, researchers compiled data from 10 surveillance systems in the European Foodborne Virus Network, finding NoV to be the cause of >85% of all acute nonbacterial outbreaks of gastroenteritis reported between 1995 and 2000. Intrinsic and extrinsic parameters commonly used by food processors include manipulation of temperature (cooking and heating, freezing, and refrigeration), water activity, pH, gaseous environment, natural and intentionally added inhibitors, and the presence of competitive microflora. Our understanding of the importance of enteric viruses in the overall burden of food-borne disease has increased dramatically over the past 20 years.
This chapter talks about marine biotoxins that can have severe impacts on health and prosperity, but effective management can minimize the risk of such impacts. It also talks about the seafood toxins includes saxitoxins, paralytic shellfish poisoning (PSP), tetrodotoxin (TTX), puffer fish poisoning, domoic acid (DOM), amnesic shellfish poisoning, brevetoxins, neurotoxic shellfish poisoning (NSP), ciguatoxins, ciguatera, okadaic acid, its derivatives, and diarrhetic shellfish poisoning (DSP). The toxins under discussion here are generally low-molecular-weight, nonprotein compounds produced by smaller organisms (generally phytoplankton) and accumulated by larger organisms that eat them. TTX and related compounds differ from the other seafood toxins discussed in the chapter, in that they appear to be endogenous or at least produced by symbionts, rather than accumulated from environmental sources. The toxicity of DOM is in part because of this strong binding and in part because the mechanisms that scavenge glutamate, keeping its concentration low and its stimulation brief, do not act on DOM. Ciguatera toxins appear to have a much stronger affinity than brevetoxins for site 5 on the voltage-activated sodium channel. The best and most comprehensive option is to use liquid chromatography–mass spectrometry (LC/MS) for detection. Most practical analyses for seafood toxins are based on high-performance liquid chromatography (HPLC), the compounds tending not to be amenable to gas chromatography. Seafood is generally wholesome but may be contaminated with potent natural toxins which can cause illness and death in consumers. Such risks can be greatly reduced by the implementation of appropriate, sustainable monitoring strategies.
This chapter discusses the formation and degradation of biogenic amines, their occurrence in foods, their significance in food safety, their potential use as quality indicators, and the available methods for their determination. The main mechanism of biogenic formation is the decarboxylation of free amino acids by specific enzymes of microbial origin, which leads to the production of amines. The concentration of available free amino acids plays a fundamental role in the formation of amines in foods, in that they are their precursors and, moreover, constitute a substrate for microbial growth. Histamine-producing microorganisms include a large number of strains from various species and families, isolated from a variety of food products. Pseudomonads are the most commonly reported bacterial group for putrescine and cadaverine formation. The addition of preservatives to foods influences the microbial population dynamics and, consequently, the production of biogenic amines. The physiological effects of tyramine include peripheral vasoconstriction, increased cardiac output, increased respiration, elevated blood glucose, and release of norepinephrine. In addition to being slightly toxic itself, tyramine reacts with monoamine oxidase (MAO) inhibitor (MAOI) drugs, giving rise to hypertensive crisis. MAO is an enzyme in the digestive tract that catalyzes the oxidative deamination of a variety of neurotransmitters as well as the monoamines of dietary origin, i.e., dopamine, phenyletylamine, serotonin, and tyramine. MAO has two subtypes, MAO-A and MAO-B, which can be found on the short arm of the X chromosome and seem to be derived from a duplication of a common ancestral gene.
The biological kingdom of the fungi contains many toxigenic species. Unlike many of the microorganisms of food safety concern, the fungi can be macroscopic, colorful, and, in this author’s opinion, beautiful and endlessly fascinating to observe. This chapter discusses species that pose the most significant food safety risks. The species include those of the filamentous fungi, also known as molds, which produce mycotoxins. The major mycotoxigenic mold genera of agronomical concern include Aspergillus, Pencillium, and Fusarium. The major food safety concerns with mycotoxins are their stability to food processing techniques and the fact that many can be transmitted through animal tissue, milk, and eggs from animals fed mycotoxin-contaminated feed. Poisonous mushrooms have been employed throughout human history for nefarious purposes. Mushrooms are becoming increasingly more prominent as cultivated foods. Mushroom amatoxins are a family of cyclic octapeptides and are produced by mushroom species including Amanita phalloides, A. virosa, and Galerina autumnalis. The mushroom toxins that cause neurological effects can cause a range of symptoms including sweating, coma, convulsions, hallucinations, excitement, depression, and spastic colon. These include some of the most infamous forms of mushroom intoxication, and cooking does not inactivate these toxins.
This chapter focuses on a specific wheat allergen and the appropriate methods for its detection in food products to demonstrate the complexity of analytical challenges that the scientific community is facing. Such challenges apply to food allergen detection in general. In this chapter, the Osborne nomenclature is used because it is most cited among immunoassay developers. In the U.S. market, gluten commercial kit providers include Neogen Corp., whose enzyme-linked immunosorbent assay (ELISA) system based on two monoclonal antibody (mAbs), for rye and wheat, and Morinaga, whose ELISA uses polyclonal antibodies for wheat proteins. The gluten test is used to demonstrate the complexity of detection methods for food allergens in processed samples and the uncertainties and implications of results. Gluten content in foods can be evaluated by either commercial ELISA kits or lateral flow devices (LFD). Four gluten levels were evaluated in this study (50, 25, 10, and 5 ppm gluten) in two different matrices, gluten-free high-fiber bread mix and matrix-free 60% ethanol. The R-Biopharm kit results can be used to illustrate the problems associated with the selection and use of reference materials. The authors have used NIST gluten SRM 8418 to evaluate the kits, and have provided a detailed discussion on the characteristics of R5 (R-Biopharm) and Skerritt (Tepnel) monoclonal Abs (mAbs) based on findings and published information. The detection of gluten proteins is quite difficult due to the complexity of the targets and specificities of the Ab.
This chapter discusses naturally occurring toxins that have been associated with the consumption of foods. The toxicity associated with ackee fruit (Blighia sapida) is due to the extremely high amounts of hypoglycin A that is present in the unripe arils (the extra seed covering) of ackee fruit. The plant part of B. sapida that is consumed is known botanically as an aril. Treatment of poisoning with ackee involves management of hypoglycemia. Proteinase inhibitors are plant, bacterial, and animal proteins that inhibit the activities of proteinases, resulting in impaired protein digestion and nutritional deficiencies in animals. Tannins are present in a number of foods, including dry beans, green peas, cereal products, leafy and green vegetables, tea, coffee, and wine. Cassava is almost always peeled, as some of the highest concentrations of cyanogens are located in the “skin” of the root. The only safe measure for sensitive individuals to avoid the toxic effects of fava beans remains to avoid “favic” agents. The chapter covers very briefly a few naturally occurring toxicants primarily from food plant sources. A clear delineation of food safety cannot be established without a comprehensive understanding of the nature and mechanism of action of each potential toxicant and the biological distinctiveness of the individual consuming it.
In this chapter, the use of the term residue relates primarily to the trace amounts of materials found in foods of various origins resulting from the application of chemicals during production. In order to focus on the type of sampling and the underlying statistical basis, the approach used for estimating the incidence of residues in animal products is presented in this chapter. The primary focus of the enforcement analytical work was related to antibiotic/antimicrobial assays and accounted for >99% of the samples. In sheep the incidence is 2.2%, approximately 2.5 times that reported in 2004, while in goats the 2005 frequency is 43% of that of 2004. A common acrylamide-forming reaction occurs when naturally occurring sugars react with asparagine at elevated temperatures. The most important point to be made is that acrylamide is considered a potential carcinogen and that the levels found in foods can be reduced during food preparation. The administration of the pesticide regulatory system is quite complex. Pesticide residues were not detected in 62.7% of domestic and 71.8% of imported samples. Of those samples, 2.4% of domestic and 6.1% of imported samples had violative levels. The problems with the U.S. food supplies are not the overall-occurring chemical residues but more likely the wide variety of bacteriological residues occurring from processing and distribution systems.
This chapter describes European contributions to food safety aspects of veterinary drugs and growth-promoting agents (GPAs). Recent developments in the area of liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS), which has become the technique of choice for surveillance of residues in food; validation of the performance of methods; and future perspectives, including the development of a risk-based surveillance program. There are several groups of substances approved for treating food-producing animals in the European Union, including antibacterials, anthelmintics, anticoccidials (or antiprotozoan drugs), sedatives, pesticides (applied as veterinary drugs), and anti-inflammatory drugs (steroidal and nonsteroidal). Legislation can be categorized into the following areas: (i) evaluation of safety, (ii) procedures for the establishment of maximum residue limits (MRLs), (iii) measures to control residues in food produced within the European Union and imported from developing countries, and (iv) guidelines for validation of analytical methods. The major deficiencies in the area of antiparasitic drug residues are that few multiresidue methods are available to detect flukicide residues and that coverage of levamisole and/or benzimidazole metabolites is often poor. A number of laboratories have developed applications using high resolution MS (HRMS) that allow the detection of several classes of veterinary drugs. Some methods include as many as 100 veterinary drug residues. The impact of such developments on methodologies and legislation will provide a clearer knowledge of exposure to veterinary drug residues through improvements in the scope of residue surveillance programs.
Prions are generally regarded as the most reliable markers of so-called prion diseases. With the advent of the protein-only concept of the transmission of prion diseases, which is predicated on the idea that prions are the infectious agents causing prion disease, and with the 1997 Nobel Prize for Medicine awarded for the prion protein concept, prions have firmly asserted their inclusion in the club of infectious agents, along with bacteria, viruses, fungi, and parasites, the club's traditional members. The essence of the protein-only theory is that the abnormal prion enters the organism and converts the host’s normal prions into abnormal prions. The efficiency of the conversion is influenced by the degree of amino acid sequence homology between the two PrPs involved, so that the greater the degree of homology, the greater the rate of conversion. Several studies suggest that white blood cells may be involved in the process. It was observed that gut-associated macrophages initially remove transmissible spongiform encephalopathy (TSE) infectivity, but once their ability to remove the infectivity completely is overcome, macrophages may facilitate the spread of infectivity. Regulatory measures introduced to prevent the spread of TSEs to humans and other animal species are likely to stay. It is possible, however, that more research and better tests will more adequately characterize risk, which in turn may lead to a gradual loosening of some of the currently existing restrictions following a carefully performed risk assessment.
This chapter focuses on biological hazards, such as viruses, parasites, bacteria, fungi, and any of their associated toxins. It should be noted that biological hazards pose the greatest public health threat at the preharvest stage since chemical and physical hazards do not reproduce and increase in the food and in the environment with time, as do microbiological hazards. Consumption of food, especially fresh foods that are not sterile, carries inherent risks of food-borne disease. Pathogens entering the chain at any stage can be transferred to the final product and result in food-borne illness. The major problem with preharvest control of food-borne pathogens is the wide variety of food products, the range of pathogens, and the complexity of environmental conditions. Vaccination of poultry against Salmonella enterica serovar Enteritidis has been effective in reducing the pathogen within flocks and eggs and indeed the incidence of salmonellosis in humans. Certain bacteria have the ability to produce and release extracellular proteins with antimicrobial properties, termed bacteriocins. Waste must be handled and stored in a manner that does not contaminate fresh produce. Manure must be obtained from an approved supplier with certification that it is processed adequately to kill pathogens. Agricultural water is used for chemical application, fertilizer application, and irrigation and does not need to be potable. Preharvest control of biological hazards in foods is a relatively new concept, although there have always been “quality assurance” programs in the production sector.
This chapter discusses the interventions applied during harvest of different food commodities. Current interventions applied in order to reduce hazards during the harvesting of beef cattle include physical and chemical treatments. Chemical dehairing is a decontamination process that involves the removal of hair from animals by using a sodium sulfide solution followed by a rinse with a hydrogen peroxide solution and water prior to dehiding. The approved methods to meet this requirement are knife trimming and vacuuming beef carcasses with hot water or steam, when such contamination is less than 1 square inch. Steam pasteurization treatments have been used in meat processing. Several chemicals with antimicrobial activity have been tested for usefulness as carcass sanitizers. The steps in poultry slaughter for which contamination is most likely to occur are the scalding and defeathering points. High-pressure processing is an alternative treatment used to eliminate pathogens from foods with no thermal pasteurization and extend the shelf life of foods. Some studies developed to test the effectiveness of radiation in decontamination of seafood have demonstrated that doses of 3 kGy or below are enough to eliminate pathogenic bacteria. There are multiple interventions for hazard control during harvest that are capable of reducing pathogenic bacteria in foods of different origin. Overall, the proper use of approved interventions/ decontamination methods will continue to enhance the safety of the food supply and allow producers to meet the demands and expectations of the consumers.
Food preservation technologies, some of which have been used for centuries to minimize deterioration of foods and to enhance their safety, include salting, heating, chilling, freezing, drying, acidifying (either directly or by fermentation), modifying packaging atmosphere, and using chemical antimicrobial compounds. The major approaches used to enhance the microbiological quality and safety of food include the application of procedures that (i) prevent or minimize access of microorganisms to the product, (ii) reduce contamination that has gained access to the product, (iii) inactivate microorganisms on the product without cross-contamination, and (iv) prevent or inhibit growth of microorganisms which have gained access and have not been inactivated, during product storage. The antimicrobial activity of essential oils or their components has also been enhanced when combined with nonthermal processing technologies, such as high-pressure processing (HPP), high-intensity pulsed electric fields (PEF), and ultrasound. Overall, non edible antimicrobial films can be classified as those that contain additives that (i) migrate to the surface of the food or (ii) are bound to the surface layer of the film and are effective against surface contamination without migration. Several other food processing technologies for microbial inactivation have been described in scientific publications. These include radio frequency heating, ohmic and conductive heating, UV light, pulsed light, ultrasound, magnetic fields, high-voltage arc discharge, and dense-phase carbon dioxide. The goal of any food preservation method is to enhance product safety, maintain product quality, and extend product shelf life by inactivating or retarding the growth of pathogenic and spoilage microorganisms.
This chapter deals with biological hazards and, more specifically, viral and bacterial pathogens. It provides an overview of the hazards and risks associated with the presence and transmission of viral and bacterial pathogens in retail-handled ready-to-eat (RTE) foods, and discusses potential control interventions. The limited number of reports of outbreaks of viral infections originating from retail-handled foods should not be considered as evidence that viral pathogens are not of importance at retail. Assurance for hazard control on incoming products can be derived from purchase specifications and supplier audits. Furthermore, good hygiene practices (GHP) including regular and thorough hand washing and use of barriers to bare-hand contact with RTE foods, such as gloves, deli wraps, and utensils, can contribute considerably to the interruption of both of the food handler-associated routes of pathogen transmission. Indeed, GHP appear to be the most important hazard control intervention, with regard to food handlers that may be asymptomatic carriers of pathogenic organisms. Effective risk communication, education, and training of food workers, supervisors, and managers are considered prerequisites for the successful implementation of hazard control measures at retail.
This chapter describes the science-based intervention strategies for a manager to use in a food service operation. Most of the chemical hazards cannot be eliminated or reduced by intervention strategies available to the cook, such as washing, peeling, or cooking food. Occasionally, there is a loss of control/deviation of the hazard control processes on the farm. The environment surrounding the facility can be contaminated with pests, birds, insects, standing water, and possible sewage backup. There can be Salmonella spp. and Listeria monocytogenes at up to an estimated 103 CFU per gram or ml. Campylobacter spp. are a common bacterial contaminant of raw poultry products. Salmonella is chosen as the target organism because it is frequently found in many foods, and the severity of the illness is high, with over two deaths per 1,000,000 people. The food safety objective (FSO) for Salmonella is to reduce it to 1 cell per 25 grams of food, or basically, a 5-log reduction. The hazard can be controlled when the customer tells the server that he/she has a sensitivity, and the server asks the cook if the food contains that ingredient and informs the customer. A regular self-inspection (daily, weekly, and monthly) must be completed to verify that intervention strategies with policies, procedures, and standards are being carried out and to determine if there are any process deviations that need corrective action.
The continued presence of pathogenic microorganisms and their toxins in food and drinking water has necessitated the ongoing need for newer, more sensitive and robust analytical systems capable of rapid detection of these contaminants in complex samples. The ideal detection method should be capable of rapidly detecting and confirming the presence of food-borne pathogenic microorganisms directly from complex samples with no false-positive or false-negative results. Rapid detection methods including immunological detection, cell/tissue-based assays and nucleic acid-based assays have been discussed in this chapter. Conventional culture techniques continue to be the gold standard for the isolation, detection, and identification of target pathogens. These methods increase detection times by hours to days, causing preliminary test results to be delayed. These assays are defined as affinity, cell/ tissue, and nucleic acid technologies. Antibody-based detection systems are still considered to be the gold standard of affinity-based testing methods. Aptamers offer several advantages over the use of antibodies in the identification of food-borne microorganisms and toxins. Any microorganism that contains DNA or RNA can be detected using nucleic acid-based assays, but a limitation of these diagnostics is their inability to detect protein-based agents of disease, such as toxins or prions.
This chapter provides an overview on molecular subtyping methods, including conventional banding-based methods and novel DNA sequence-based methods, to molecularly confirm that isolates belong to a given food-borne bacterial pathogen and to discriminate among isolates belonging to a given food-borne bacterial pathogen. It discusses about molecular subtyping methods which will be grouped into two categories: (i) conventional banding-based or DNA fingerprint-based methods and (ii) DNA sequence-based methods. DNA sequencing of one or more genes or the whole genome, probing the presence of specific repeat sequences, sequence-specific hybridizations, and differentiating allelic types from single-nucleotide polymorphisms (SNPs) represent DNA sequence-based molecular subtyping methods used to differentiate food-borne pathogens. SNP typing assays may be developed to directly target nucleotides that have been shown to discriminate allelic types. Another major advantage of SNP typing over conventional banding-based or other DNA sequence-based molecular subtyping techniques is that SNP genotyping assays can be designed to target slowly accumulated genetic variations in protein-coding genes (e.g., synonymous mutations), providing the most reliable inference of genetic relatedness. In addition, DNA sequence-based subtyping techniques (particularly multilocus sequence typing (MLST) and multiple-locus variable-number tandem repeat analysis (MLVA) typing schemes) are becoming more standardized across laboratories and databases that contain DNA sequenced-based molecular subtyping data continue to rapidly expand. Multiplexed SNP typing assays that differentiate allelic types based on SNPs present within housekeeping genes known to diversify on an evolutionary time scale show great promise to characterize food-borne pathogens.
Food safety management can be viewed from different levels: broadly from the perspective of government food safety management systems or more narrowly from that of industry-wide food safety management systems or that of food safety management within an individual establishment. The role of the food industry is to provide safe foods; industry is responsible for establishing food safety management systems that ensure that foods present a minimal risk to the consumer. Risk analysis allows the development of risk-based metrics, such as food safety objectives (FSOs), performance objectives (POs), and performance criteria (PCs), which are addressed in this chapter. Seven hazard analysis and critical control point (HACCP) principles form the framework of a systematic approach to ensure the determination and control of significant food safety hazards associated with a product and process. Monitoring is the first line of defense in the preventive HACCP system. In addition to those related to GMP or sanitation regulations, prerequisite programs can include other programs, such as ingredient specifications, consumer complaint management, glass control programs, allergen management programs, microbiological monitoring of the plant environment, ingredient-to-product traceability programs, and supplier approval programs. PCs can easily be translated into product or process criteria by industry or by government. In integrating a farm-to-fork food safety system, there will be a variety of metrics at points along the food chain.
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There is no such thing as an over-crowded market in publishing and this certainly appears to be the view of those concerned with commissioning and editing books on microbiological food safety. Here we have another which has assembled an international collection of authors to contribute chapters on the principal pathogens and toxins in foods. Allergens and veterinary drug residues and growth promoters are included in the latter and also have their own chapters. A fairly uniform format is employed to give up-to-date information describing individual pathogens, their source and distribution, the illness they cause and the factors that affect their growth, etc. Individual chapters also have a section reviewing recent advances in biological, chemical and physical control methods.
What is most novel in the approach adopted here is a series of general cross-cutting chapters describing hazard control options at various points in the food production chain: preharvest, during harvest, during processing, retailing ready-to-eat foods and food service, as well as a general over view of food safety management systems. It is fair to say that much of the material in this book is available elsewhere but it is an up-to-date and comprehensive compilation which will prove a useful library purchase where budgets permit.
Society for General Microbiology: Microbiology Today
Reviewer: Martin Adams, University of Surrey
Review Date: 2009
At A Glance
"Pathogens and Toxins in Foods: Challenges and Interventions" offers a farm-to-table approach to food safety that enables readers to control microbial pathogens and toxic agents at all stages of the food supply chain. The book begins with chapters that help readers understand the characteristics of specific pathogens and toxins, the illnesses they cause, and the factors such as food processing operations that affect their survival and growth in food products. Further, the chapters in the book explore the most recent advances in biological, chemical, and physical interventions to control food-borne hazards during preharvest, harvest, food processing, and in retail ready-to-eat foods and food service operations. Also included are chapters that discuss the latest methods to rapidly detect food-borne pathogens as well as the implementation of comprehensive food safety management systems. Each chapter has been written by one or more leading experts in the field of food safety. Their advice is based on a thorough investigation of the literature as well as their own first-hand experience. In short, by drawing from hundreds of sources, this book offers food safety professionals a unique, single reference containing the latest understanding of food-borne hazards as well as the latest methods to detect and control their incidence. This title investigates the microbial pathogens and toxic agents that threaten the global food supply. It covers all stages of the food supply chain from farm to table. It presents tested and proven intervention strategies to control food-borne hazards. It offers sound advice based on an analysis of the latest findings from the scientific literature. It sets the foundation for new approaches to control food-borne hazards and decrease the incidence of food-borne illnesses.
Description
The complexity of food processing makes it a challenge to control and monitor for contamination with harmful microbial agents or toxins. This book reviews the infectious agents and toxins that can contaminate food and the methods used to control them.
Purpose
This book is designed to inform readers about the variety of methods used to survey food products for toxic agents, which includes the application of various tests as well as methods of processing that decrease contamination.
Audience
This would be appropriate for students studying food processing as well as for industry and research applications. All of the authors have experience in these areas and have brought their expertise to this topic with clarity and enthusiasm.
Features
The book describes each of the potential microbial agents or toxins that have been found to contaminate food products. These are a variety of different organisms or chemicals that are found naturally in the environment but cause serious harm to humans when they are ingested. The first sections provide a great amount of detail on the bacterial contaminants found in food, which include the ubiquitous Bacillus species and toxin-producing Clostridia species, as well as the enteric bacteria such as Campylobacter, Salmonella, and E. coli. Interestingly, this is followed by a discussion of parasitic agents and fungal agents that can contaminate food products. These chapters contain very good, detailed diagrams of the lifecycles of the agents as well as detailed tables. The book also discusses the potential for seafood toxins from phytoplankton to contaminated shell fish. Each chapter contains good information on the detection methods used for each contaminant.
Assessment
This is a well-designed book with information on food contamination that will be valuable to any individuals involved in food production or research on food production.
Doody Enterprises
Reviewer: Rebecca Horvat, PhD, D(ABMM) (University of Kansas Medical Center)
Review Date: Unknown
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