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University of Baghdad College of Veterinary Medicine Dept. of Vet. Public Health/ Food Hygiene Foodborne Infections Foodborne infection occurs from the consumption of food (and water) contaminate...

University of Baghdad College of Veterinary Medicine Dept. of Vet. Public Health/ Food Hygiene Foodborne Infections Foodborne infection occurs from the consumption of food (and water) contaminated with pathogenic enteric bacteria and viruses. Many pathogens are included in this group. However, many are involved more frequently than others, and they are discussed in this lecture. The discussions include their relative importance, characteristics, food association, toxins, disease symptoms, and prevention. For some, detection methods and case histories are also included. The following are some characteristics of foodborne infections: 1. Live cells of the enteric pathogens (bacteria and viruses) have to be consumed through food. 2. The surviving cells (from gastric environment) penetrate through the membrane and establish in the epithelial cells of the intestines, multiply, and produce toxins (infection). 3. Dose levels that cause infection vary greatly. Theoretically, one live cell has the potential to produce the disease. Experts estimate that consumption of 10 cells (for an extremely virulent species and strain, such as Escherichia coli O157:H7) to 105 cells or more (for a less virulent species and strain, such as Yersinia enterocolitica) might be required for the disease. 4. Symptoms generally occur after 24 h, which, depending on the pathogen, and can be both enteric and nonenteric in nature. 5. Enteric symptoms are local and due to enteric infection and the effect of toxins. Symptoms include abdominal pain, diarrhea (sometimes accompanied with blood), nausea, vomiting, and fever. Examples of pathogens include Salmonella, Shigella, 1 enteroinvasive Esc. coli (EIEC), Vibrio parahaemolyticus, Campylobacter jejuni, and Yer. enterocolitica. 6. Nonenteric symptoms (along with enteric symptoms) result when the pathogens or their toxins pass through the intestine and invade or affect other internal organs and tissues. Symptoms depend on the types of organs and tissue affected, but are accompanied by fever. Examples of pathogens include Listeria monocytogenes, enterohemorrhagic Esc. coli (EHEC), Vib. vulnificus, and Hepatitis A virus. SALMONELLOSIS BY SALMONELLA A. Importance Before the 1940s, Salmonella typhi and Sal. paratyphi were considered the major causes of worldwide foodborne and waterborne diseases caused by Salmonella in humans. However, with the pasteurization of milk and chlorination of water supplies, the spread of typhoid and paratyphoid fever through food and water was greatly reduced, at least in the developed countries. As efficient techniques to isolate and identify other Salmonella serovars from foods and environmental samples were developed, it became apparent that the worldwide incidence of foodborne salmonellosis caused by other Salmonella is quite high. Since the 1950s, foodborne salmonellosis has been recognized to be the major cause of all foodborne diseases by pathogenic bacteria and viruses, both in number of incidents (sporadic and outbreaks) and number of cases. Although, at present, scientific information about the habitats, mode of transmission in foods, growth characteristics, and survival parameters of the pathogen are available, and methods to control its contamination of foods have been developed, The control measures seem to be working for several other foodborne pathogens, at least in the U.S., such as Clostridium perfringens, Bacillus cereus, Yer. enterocolitica, Vib. parahaemolyticus, and probably Staphylococcus aureus. Even incidences from Sta. aureus and Lis. monocytogenes seemed to have declined since the 1990s. It is somewhat astonishing that control measures are not working against Salmonella. Not only does the incidence not decrease, but it continues to increase at a high rate. It is difficult to pinpoint the exact causes of this increase. It may be related to the large number of 2 serotypes present in high frequency in carrier state in food animals, birds, pets, insects, humans, and their ability to grow in foods; the way the food animals and birds are raised, processed, and marketed; better surveillance systems by regulatory agencies; or our lifestyles and food habits giving these pathogens an edge. Several studies indicated that the present increase in salmonellosis (including foodborne salmonellosis) in the U.S. could be related to four factors: (1) increase in number of antimicrobial-resistant Salmonella isolates, (2) increase in immunodeficient individuals who are extremely susceptible to Salmonella, (3) increase in egg- associated Salmonella Enteritidis contamination due to increase in laying hens with infected ovaries, and (4) food production in centralized facilities that can lead to, if contamination occurs, extremely large and widespread outbreaks. It is necessary to understand the importance of these factors in the increase of salmonellosis and to develop corrective measures to control the incidence. B. Characteristics Salmonella cells are Gram-negative, nonsporulating, facultative anaerobic, motile rods. They form gas while growing in media containing glucose. Generally, they do not ferment lactose; utilize citrate as a carbon source; produce hydrogen sulfide, decarboxylate lysine, and ornithine; do not produce indole; and are negative for urease. They are mesophilic, with optimum growth temperature between 35 and 37oC, but generally have a growth range of 5 to 46oC. They are killed by pasteurization temperature and time, sensitive to low pH (4.5 or below), and do not multiply at an Aw of 0.94, especially in combination with a pH of 5.5 and below. The cells survive in frozen and dried states for a long time. They can multiply in many foods without affecting the acceptance qualities. C. Habitat Salmonellae are natural inhabitants of the gastrointestinal tracts of domesticated and wild animals, birds, and pets (including turtles and frogs), and insects. In animals and birds, they can cause salmonellosis and then persist in a carrier state. Humans can also be carriers following an infection and shed the pathogens through feces for 3 a long time. They have also been isolated from soil, water, and sewage contaminated with fecal matters. D. Toxins Following ingestion of Salmonella cells, the pathogens invade mucosa of the small intestine, proliferate in the epithelial cells, and produce a toxin, resulting in an inflammatory reaction and fluid accumulation in the intestine. Once inside the epithelial cells, the pathogens multiply and produce a thermolabile enterotoxin that is directly related to the secretion of fluid and electrolytes. Production of the enterotoxin is directly related to the growth rate of the pathogens. E. Disease and Symptoms foodborne salmonellosis, an individual generally has to consume 105–6 cells; however, for some virulent strains, ingestion of fewer cells can cause the disease. Strains sensitive to gastric acidity generally need more cells to establish in the intestine and cause the disease; conversely, acid resistant strains may require fewer cells to cause the disease. Following ingestion of the pathogen, symptoms appear in 8 to 42 h, generally in 24 to 36 h. Symptoms last for 2 to 3 days, but in certain individuals can linger for a long time. An individual remains in a carrier state for several months following recovery. Not all individuals ingesting the same contaminated foods develop symptoms, and those who develop symptoms do not have all the symptoms in the same intensity. Susceptibility varies with the state of health and natural resistance of an individual. The general symptoms are abdominal cramps, diarrhea, nausea, vomiting, chills, fever, and prostration. It can be fatal, especially to the sick, infants, and the elderly. F. Food Association Foods of animal origin have been associated with large numbers of outbreaks. These include beef, chicken, turkey, pork, eggs, milk, and products made from them. In addition, many different types of foods have been implicated in both sporadic cases and outbreaks. These foods were contaminated directly or indirectly with fecal matters from carriers (animals, birds, and humans) and eaten either raw or 4 improperly cooked, or contaminated following adequate heat treatment. Cross contamination at home and at food services are the major sites of contamination of heated foods with Salmonella. Salmonellae have also been isolated from many foods of plant origin (use of sewage as fertilizer or washing products with polluted water), seafood, (harvested from polluted water). Although there are more than 2000 serotypes of Salmonella, only some of them have been frequently associated with foodborne illnesses. This can be because of geographical distribution of the serotypes as well as pathogenicity of a serovar or a strain. In the U.S., Salmonella Typhimurium has been considered the major causative agent of foodborne salmonellosis (more than 20% of the total cases). However, since the 1980s, foodborne salmonellosis from Salmonella Enteritidis has increased, mainly from contaminated eggs. In recent years, it has been involved in the same number of cases as Salmonella Typhimurium. The exact cause of the predominance of Salmonella Enteritidis is not yet clearly understood. The methods used in raising food of animals and birds and in processing of foods of animal origin are suspected to have an important role. G. Prevention and Control Raw foods of animal origin that are heat treated before consumption can have Salmonella. However, in the U.S. (and other developed countries), as per regulatory requirements, heat-treated and ready-to-eat foods that contain Salmonella in portions (samples) tested are considered to be adulterated and should not be sold. Regulatory agencies also have programs to educate consumers at home and food handlers in food service places to control Salmonella contamination in foods. These include proper cooking of foods (minimum to pasteurization temperature and time, such as 71.7oC for 15 sec or equivalent) and prompt cooling (to 3 to 4oC or freezing); preventing cross-contamination of ready-to-eat food with a raw food through cutting boards, equipment, utensils, and hands; using proper sanitation and personal hygiene; sick people not handling a food; and properly reheating a food refrigerated for a long time. 5 PATHOGENIC ESCHERICHIA COLI A. Importance Since its discovery in 1885, Escherichia coli was considered a harmless, Gram negative, motile, nonsporulating, rod-shaped, facultative anaerobic bacterium, a normal inhabitant of the intestinal tract of humans and warm-blooded animals and birds. Because it is normally present at a very high level (in millions per gram of the content of the large intestine), for a long time it has been used as an index organism for possible fecal contamination and presence of enteric pathogens in food and water. Since the mid-1940s, evidence has accumulated that certain Esc. coli strains cause diarrhea, particularly in infants, and they were designated as enteropathogenic Esc. coli. However, current evidence indicates that pathogenic strains of Esc. coli are more than one type. They are subdivided into four groups. Recently, they have been subdivided into six groups, including the four discussed here, together with the enteroaggregative Esc. coli (EAggEC) and diffuse-adhering Esc. coli (DAEC). 1. Enteropathogenic Esc. coli (EPEC) These strains are important in infant diarrhea worldwide, especially in places with poor sanitation. They are transmitted directly or indirectly through human carriers. Several serotypes are implicated in waterborne and foodborne disease outbreaks in different countries. The pathogenesis is produced by their ability to form a close contact with the intestinal epithelial cells and cause lesions. One needs to ingest high numbers of cells (106–9) to develop symptoms. The predominant symptomis gastroenteritis. 2. Enterotoxigenic Esc. coli (ETEC) These strains are the major cause of diarrhea in travelers, as well as in infants in many developing countries with poor sanitation. The pathogens produce an invasive factor and a heat-labile (HL), a heat-stable (HS), or both HL and HS, enterotoxins to cause the disease. The symptom is gastroenteritis, like a mild form of cholera. The pathogen is spread directly or indirectly by human carriers. Both food and water 6 have been implicated in outbreaks and sporadic cases in humans. In 1983, imported Brie cheese contaminated with O27:H7 serotype caused outbreaks in several countries, including the U.S. Ingestion of large numbers of cells (108–9) is necessary for an individual to develop symptoms. 3. Enteroinvasive Esc. coli (EIEC) These strains are known to cause dysentery similar to that that caused in shigellosis. The ability of the strains to produce an invasive factor is thought to be the cause of the disease. Human carriers, directly or indirectly, spread the disease. Ingestion of as many as 106 cells may be necessary for an individual to develop symptoms. An outbreak in the U.S. as early as 1971 was recognized from the consumption of imported Camembert cheese contaminated with serotype O124:B17. 4. Enterohemorrhagic Esc. coli (EHEC) The strains in this group (a principal serogroup is O157:H7) have been recognized relatively recently as the cause of severe bloody diarrhea (hemorrhagic colitis) and hemorrhagic uremic syndrome (HUS) in humans. Animals, particularly dairy cattle, are thought to be the carriers. Ingestion of as few as 10 to 100 cells can produce the disease, especially in sensitive individuals. Three enterotoxins (verotoxins) produced by the serotype cause the disease symptoms. B. Gastroenteritis Due to EIEC 1. Toxins The pathogens produce several polypeptides, the genes of which are encoded in a plasmid. These are considered to be the invasive factors that enable the pathogen to invade epithelial cells and set up infection in the colon. Separate toxins have not yet been identified. 2. Disease and Symptoms The disease and symptoms are similar to those for shigellosis. Following ingestion of the pathogen (106 cells) and incubation period, symptoms appear as abdominal 7 cramps, profuse diarrhea, headache, chills, and fever. A large number of pathogens are excreted in the feces. Symptoms can last for 7 to 12 d, but a person can remain a carrier and shed the pathogens in feces for a long time. 3. Food Association Only humans are known to be the host of the pathogen, and a food can get contaminated directly or indirectly though fecal contamination. Outbreaks from the ingestion of foods contaminated with the pathogen have been recorded. The 1971 outbreak in the U.S. from the ingestion of an imported cheese was traced to contamination of the processing plant equipment from a malfunctioning water filtration system. In 1983, another outbreak on a cruise ship was related to potato salad contaminated by a carrier food handler. 4. Prevention The pathogen is sensitive to pasteurization temperature. Thus, proper heat treatment, elimination of post heat contamination for a ready-to-eat food, and refrigeration of a food soon after preparation are necessary to control the disease. In addition, proper sanitation at all stages of food processing and handling is an important factor. Individuals suspected of being carriers should not handle food, especially ready-to eat food. C. Gastroenteritis due to EHEC 1. Characteristics The principal serotype associated with enterohemorrhagic colitis is Esc. Coli O157:H7. As opposed to other Esc. coli, it does not ferment sorbitol or have glucuronidase activity. Like other Esc. coli, it grows rapidly at 30 to 420C, grows poorly at 44 to 450C, and does not grow at 10oC or below. Strains resistant to pH 4.5 or below have been identified. The organism is destroyed by pasteurization temperature and time and killed at 64.3oC in 9.6 sec. The cells survive well in food at –20oC. 8 2. Toxins Esc. coli O157:H7 produces a verotoxin (VTI), or Shiga toxin (ST). For this, it is also designated as VTEC or STEC. More than one toxin can be involved in the disease and the symptoms related to it. It is not known whether the pathogen also produces invasive factors. The cells probably colonize in the intestine by adhering to the epithelial cells and produce toxins, which then act on the colon. Toxins are also absorbed into the bloodstream and damage the small blood vessels in the intestine, kidneys, and brain. 3. Disease and Symptoms Esc. coli O157:H7 causes hemorrhagic colitis, hemolytic uraemic syndrome (HUS), and thrombotic thrombocytopenic purpura (TTP). Symptoms occur 3 to 9 d after ingestion and generally last for 4 d. The colitis symptoms include a sudden onset of abdominal cramps, watery diarrhea (which in 35 to 75% of cases turns to bloody diarrhea), and vomiting. Fever may or may not be an associated symptom. Damage to the lining of the large intestine causes bleeding. Toxins also cause breakdown of red blood cells, and clotting in small blood vessels of the kidney, causing kidney damage and occasional kidney failure, causing HUS. It can be fatal, particularly in children. TTP results from a blood clot in the brain, with seizures, coma, and often death. 4. Food Association The pathogen is probably present in the intestine of animals, particularly in dairy cattle, without producing symptoms. Food of animal origin, especially ground beef, has been implicated in many outbreaks in the U.S., Europe, and Canada. The affected people were found to have consumed improperly cooked, contaminated hamburgers. In a 1993 outbreak, affecting over 500 people and causing 4 deaths, consumption of hamburgers served by a fast-food chain in Washington, Nevada, Oregon, and California was implicated. The hamburgers, contaminated with Esc. coli O157:H7, were cooked at a temperature that failed to kill the pathogen. In addition to ground beef, other foods, such as raw milk, apple cider, some fruits, uncooked 9 sausages, and salad have been implicated. Investigations revealed the presence of Esc. coli O157:H7 in many different types of foods of animal origin, such as ground beef, pork, poultry, lamb, and raw milk, in low percentages. The organism was isolated in low frequencies from dairy cows as well as calves and chickens. 5. Prevention Proper sanitation, cooking or heating at appropriate temperatures, proper refrigeration, and prevention of cross-contamination should be practiced in order to control the presence of Esc. coli O157:H7 in a ready-to-eat food. The Food Safety Inspection Service (FSIS) in the U.S. has provided the following guidelines to control foodborne illness from this pathogen: use only pasteurized milk; quickly refrigerate or freeze perishable foods; never thaw a food at room temperature or keep a refrigerated food at room temperature over 2 h; wash hands, utensils, and work areas with hot soapy water after contact with raw meat; cook meat or patties until the center is gray or brown; and prevent fecal–oral contamination through proper personal hygiene. SHIGELLOSIS (BACILLARY DYSENTERY) BY SHIGELLA SPP. A. Importance The genus Shigella contains four species: Shigella dysenteriae, Shi, flexneri, Shi. boydii and Shi. sonnei and each species has several serovars. Only humans and some primates are their hosts. The organisms are either transmitted directly through fecal–oral routes or indirectly through fecal-contaminated food and water. While in most developed countries transmission through drinking water has been reduced, in developing countries contaminated drinking water is a major cause of shigellosis. The disease is prevalent in some geographic locations, particularly in Asia, Mexico, and South America. It occurs more frequently in places with poor sanitation. Children below 5 years of age are,more affected. In developing countries, there is a high fatality rate among children suffering from shigellosis. 10 In general, food service establishments have been implicated in more outbreaks, and poor personal hygiene has been the major cause. The disease is more predominant during late spring to early fall. B. Characteristics The cells of the species are Gram-negative, nonmotile, facultative anaerobic rods. They are generally catalase positive and oxidase and lactose negative. They ferment sugars, usually without forming gas. The strains grow between 7 and 46oC, with an optimum at 37oC. They survive for days under different physical and chemical stresses, such as refrigeration, freezing, 5% NaCl, and pH 4.5. They are killed by pasteurization. The strains can multiply in many types of food when stored at growth temperature range. C. Habitat The intestine of humans and some primates is the only habitat known. Humans can carry the organism in the intestine, and shed it in the feces without showing any symptoms. Following recovery from shigellosis, an individual can remain a carrier for months. D. Toxins The strains are believed to carry plasmid-encoded invasive traits that enable the shigellae cells to invade epithelial mucosa of the small and large intestines. Once engulfed by the epithelial cells, they can produce an exotoxin that has an enterotoxigenic property. The toxin is designated as Shiga toxin (ST). The invasive trait is expressed at 37oC but not at 30oC. Shigellae cells growing at 30oC need a few hours of conditioning at 37oC before they can invade intestinal epithelial cells. The engulfed shigellae cells kill the epithelial cells and then attack fresh cells, causing ulcers and lesions. E. Disease and Symptoms The infective dose is very low, 101–3 cells in adults. Following ingestion of a contaminated food, the symptoms occur in 12 h to 7 d, but generally in 1 to 3 d. In 11 case of mild infection, symptoms last for 5 to 6 d, but in severe cases, symptoms can linger for 2 to 3 weeks. Certain individuals might not develop symptoms. An infected person sheds the pathogens long after the symptoms have stopped. The symptoms are the consequence of both invasiveness of epithelial mucosa and the enterotoxin and include abdominal pain, diarrhea often mixed with blood, mucus and pus, fever, chills, and headache. Generally, children are more susceptible to the disease than adults. F. Food Association Shigella cells are present in a food only through fecal contamination, directly or indirectly, from a person either suffering from the disease, or a carrier or a person who has not developed symptoms yet but is shedding the pathogens in feces. Direct contamination occurs from poor personal hygiene. Indirect contamination occurs from the use of fecal-contaminated water to wash foods that are not subsequently heat processed. Also, cross-contamination of ready-to-eat foods can be involved in an outbreak. Foods often implicated in shigellosis are those that are handled too much and are ready-to-eat. In many developed countries, the most frequently involved foods are different types of salads (potato, tuna, shrimp, and chicken ). Foods that are chopped, diced, or cut prior to eating, such as vegetables used in salads, have also been involved in outbreaks. Shellfish harvested from sewage polluted water and eaten raw have been associated with shigellosis. Many foods support their growth. As the infective dose is very low, growth in food is probably not an important factor for the disease. G. Prevention Foodborne shigellosis, at least in the developed countries, is caused by contamination of foods by food handlers shedding the pathogen in the feces and having poor personal hygiene. To prevent contamination of ready-to-eat food by such individuals, it is necessary to forbid them to handle such foods. Quite often, this is impossible, especially if the individual is a carrier. Proper education of the food handlers about the importance of good personal hygiene and the need to not handle food if one suspects having a digestive disorder is important. Use of rigid 12 sanitary standards to prevent cross-contamination of ready-to-eat food, use of properly chlorinated water to wash vegetables to be used for salads, and refrigeration of foods are necessary to reduce foodborne shigellosis. CAMPYLOBACTERIOSIS BY CAMPYLOBACTER SPP. (CAMPYLOBACTER ENTERITIS AND CAMPYLOBACTER JEJUNI ENTERITIS) A. Importance Several Campylobacter species can cause human gastroenteritis; however, Campylobacter jejuni and Cam. coli are considered the most common causative agents of human diarrheal disease in many countries worldwide. Cam. jejuni has been confirmed as a causative agent in many foodborne illnesses. Since it was first recognized as the cause of an outbreak in 1979, The foods implicated most often in campylobacteriosis were raw milk and improperly cooked chicken. Although several Campylobacter spp. have been associated with foodborne campylobacteriosis, Cam. jejuni has been isolated in most incidents; the discussion here is on Cam. jejuni. B. Characteristics Cam. jejuni is a Gram-negative, motile, nonsporulating, rod-shaped bacterium. The cells are small, and spirally curved. The strains are microaerophilic and catalase and oxidase positive. The strains require a microaerophilic environment of. 5% oxygen, 8% CO2, and 87% N2 for growth. Growth temperature ranges between 32 and 45oC, with optimum 42oC. They grow better in amino acids than in carbohydrates. They generally grow slowly and are not a good competitor while growing with other bacteria. They do not generally grow well in many foods. They are sensitive to many environmental parameters, including oxygen (in air), NaCl (above 2.5%), low pH (below pH 5.0), temperature (below 30oC), heat (pasteurization), and drying. However, they survive well under refrigeration and for months in the frozen state. C. Habitat Cam. jejuni is an enteric organism. It has been isolated in high frequency from feces of animals and birds. Human carriers were also found to shed the organisms in feces. 13 Fecal materials from poultry were found to contain 106 cells/g in some instances. Water, sewage, vegetables, and foods of animal origin are easily contaminated with Cam. jejuni excreted through feces. D. Toxins Cam. jejuni has a thermolabile enterotoxin that is responsible for enteric disease symptoms. In addition, the strains produce an invasive factor that enables the cells to invade and establish in epithelial cells in both the small and large intestines in humans. E. Disease and Symptoms The infective dose for campylobacteriosis is considerably low, only 500 cells. Following ingestion, symptoms of the disease occur in 2 to 5 d. Symptoms generally last for 2 to 3 d, but can longer for 2 weeks or more. Persons with no visible symptoms can shed the cells in feces for a long time. The main symptoms are enteric and include abdominal cramps, profuse diarrhea, nausea, and vomiting. Other symptoms include fever, headache, and chills. In some cases, bloody diarrhea has been reported. F. Food Association Because the organism is present in high frequency in animals, birds, and the environment, many foods, both from plant and animal sources, can be contaminated with Cam. jejuni. The foods can be contaminated directly with fecal material from animals and infected humans or indirectly from sewage and contaminated water. Cam. Jejuni has been isolated at a very high frequency from raw meats (beef, lamb, pork, chicken, and turkey), milk, eggs, vegetables, mushrooms, and clams. In heat-processed food, their presence has been related to cross-contamination following heat treatment or to improper heating. The use of animal feces as fertilizers was found to contaminate vegetables. Outbreaks of campylobacteriosis result from the consumption of raw milk, improperly cooked chicken, dairy products, bakery products, turkey products, eggs, and others. Consumption of raw milk and chicken were implicated in many outbreaks. Although 14 the organism is a poor competitor against other microorganisms present in a food and generally does not grow well in foods, enough cells can survive in a contaminated food to provide the dose required for the disease. G. Prevention It is rather difficult to control the access of Cam. jejuni to raw foods, particularly foods of animal origin. However, proper sanitation can be used to reduce its load in raw foods during production, processing, and future handling. Preventing consumption of raw foods of animal origin, heat-treatment of a food, when possible, and preventing post heat contamination are important to control campylobacteriosis in foods of animal origin. Contamination of vegetables can be controlled by not using animal feces as fertilizer and not using contaminated water to wash vegetables (especially ready-to-eat types). Contamination from humans can be reduced by establishing good personal hygiene and not allowing sick individuals to handle foods, especially ready-to-eat foods. 15