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Foodborne Infections. Characteristics of Foodborne Infections. Live cells of the enteric pathogens(bacteria and viruses) have to be consumed through food.

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characteristics of foodborne infections
Characteristics of Foodborne Infections

Live cells of the enteric pathogens(bacteria and viruses) have to be consumed through food.

The surviving cells(from gastric environment) penetrate through the membrane and establish in the epithelial cells of the intestines, multiply and produce toxins(infection).

Dose levels that cause infection vary greatly. e.g.

10 cells from virulent E. coli 0157:H7 might be required for disease.

Symptoms generally occur after 24 h, which, depending on pathogen, can be both enteric and nonenteric in nature.


Enteric symptoms are local and due to enteric infection and the effect of toxins. Symptoms include abdominal pain, diarrhea, nausea, vomiting, and fever. Examples of pathogens include Salmonella, Shigella, enteroinvasive E. coli(EIEC), Vibrio parahaemolyticus, Campylobacter jejuni, and Yersinia enterocolitica.

Nonenteric symptoms result when the pathogens or their toxins pass through the intestine and invade other internal organs. Symptoms depend on the affected tissue, but are accompanied by fever. Examples of pathogens include Listeria monocytogenes, enterohemorrhagicE. coli(EHEC), hepatitis A virus.

pathogenic escherichia coli
Pathogenic Escherichia coli

E. Coli is Gram negative, motile, nonsporulating, rod-shaped, facultative anaerobic bacterium.

E.Coli is a normal inhabitant of the intestinal tract of humans, warm-blooded animals and birds.

E.Coli is used as an index organism for possible fecal contamination and presence of enteric pathogens in food and water.

Certain E.coli strains are pathogenic and cause diarrhea.

pathogenic groups of e coli
Pathogenic Groups Of E. coli

Enteropathogenic E. coli(EPEC)

These strains are important in infant diarrhea worldwide, especially in places with poor sanitation.

They cause waterborne and foodborne disease outbreaks in different countries.

They have the ability to form a close contact with the intestinal epithelial cells and cause lesions. The predominant symptom is gastroenteritis.

The infectious dose exceeds several million cells.

enterotoxigenic e coli etec
Enterotoxigenic E. coli(ETEC)

These strains are the major cause of diarrhea in travelers and infants where there is poor sanitation.

The pathogens produce an invasive factor and heat labile(HL) and heat stable(HS) or both enterotoxins.

The symptom is gastroenteritis, like a mild form of cholera.

The pathogen is spread by human carriers.

Ingestion of several millions of cells is necessary to cause disease.

enteroinvasive e coli eiec
Enteroinvasive E. coli(EIEC)

These strains cause dysentery similar to that caused in shigellosis.

They produce an invasive factor which is the cause of the disease.

Human carriers spread the disease.

Ingestion of one million cells is necessary for an individual to develop symptoms.

enterohemorrhagic e coli ehec
Enterohemorrhagic E. coli(EHEC)

The strains in this group(a principal serogroup is (0157:H7) produce powerful toxins causing bloody diarrhea(hemorrhagic colitis) due to the damage of the lining of large intestine and hemorrhagic uremic syndrome (HUS) in humans. HUS results from hemolyzed RBCs and clotting in small blood vessels of the kidney leading to kidney damage and occasionally kidney failure, it can be fatal , particularly in children.

Animals, particularly dairy cattle, are thought to be the carriers.

Ingestion of as few as 10-100 cells can produce the disease. Enterotoxins(verotoxins or shiga toxin ;VTEC or STEC) produced by the serotype cause the disease symptoms. Toxins are absorbed into the blood stream and damage the small blood vessels in the intestine, kidneys and brain.


Pasteurization of milk

Refrigeration or freezing of perishable foods

Never thaw a food at room temperature or keep a refrigerated food at room temperature over 2h

Wash hands, utensils, and work areas with hot soapy water after contact with raw meat

Prevent fecal-oral contamination through proper personal hygiene.

Proper sanitation at all stages of food processing and handling

Individuals suspected of being carriers should not handle food, especially ready-to-eat.

shigellosis bacillary dysentery
Shigellosis(Bacillary Dysentery)

The genus Shigella contains four species:





The organisms are either transmitted directly through fecal-oral routes or indirectly through fecal-contaminated food and water.

Shigellosis occurs more frequently in places with poor sanitation.


Gram-negative, nonmotile, facultative anaerobic rods, catalase positive, oxidase and lactose negative. They ferment sugars without gas.

The strains grow between 7-46C with an optimum at 37C.

They survive for days under refrigeration, freezing, 5% NaCl, pH 4.5.

They are killed by pasteurization.

The strains can multiply in many foods when stored at growth temperature range.

Following recovery, a person can remain a carrier for months.


Shigella can invade epithlial mucosa of the small and large intestines.

Once engulfed by the epithelial cells, they can produce an exotoxin that has an enterotoxigenic properties.

The toxin is known as Shiga toxin(ST). It is expressed at 37C.

The engulfed shigellae cells kill the epithelial cells and then attack fresh cells, causing ulcers and lesions.


The infective dose is very low(10-1000 cells)

Symptoms occur in 1-3 days

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. Children are more susceptible than adults.

Foods implicated in shigellosis are those that are handled too much and are ready to eat. As the infective dose is very low, growth in food is probably not an important factor for the disease.

Prevention like pathogenic E. coli.


Foodborne salmonellosis is the leading cause of foodborne bacterial and viral diseases in the U.S.A and other developed countries.

It may be related to the large number of 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.

The present increase in salmonellosis could be related to four factors; increase in number of antimicrobial-resistant Salmonella isolates, increase in immunodeficient individuals, increase in laying hens with infected ovaries, food production in centralized facilities that can lead to, if contamination occurs, extremely large and widespread outbreaks.


There are more than 2000 serovars(based on somatic, flagellar, and capsular antigen types) of Salmonella, potentially capable of causing salmonellosis in humans. Along with fecal-oral direct transmission, contaminated food and water can cause salmonellosis.


Salmonella cells are Gram-negative, nonsporulating, facultative anaerobic, motile rods, they form gas while growing in media containing glucose, they ferment dulcitol but not lactose, utilize citrate as a carbon source, produce H2S, decarboxylate lysine and ornithine, do not produce indole and are negative for urease.


Salmonella are mesophilic with optimum growth temperature between 35-37C, with growth range of 5-46C, they are killed by pasteurization temperature, sensitive to low pH.

The cells survive in frozen and dried states for a long time.

They can multiply in many foods without affecting the acceptance qualities.

Salmonellae are natural inhabitants of the GIT of domisticated and wild animals, birds and pets and insects. In humans and animals they cause salmonellosis and then persist in a carrier state. They have also been isolated from soil, water and sewage contaminated with fecal matters.

toxins and disease
Toxins and disease

Following ingestion of Salmonella cells, the pathogens invade mucosa of the small intestine, proliferate in the epithelial cells, resulting in an inflammatory reaction and fluid accumulation in the intestine.

The ability of the pathogens to invade and damage the cells is due to the production of a thermostable cytotoxic factor.

Once inside the epithelial cells, the pathogen multiply and produce a thermolabile enterotoxin that causes the secretion of fluid and electrolytes.


For foodborne salmonellosis, the infectious dose is around one million cells, for more virulent strains, ingestion of fewer cells can cause the disease.

Symptoms appear in 24-36 h, symptoms last for 2-3 days, an individual remains in a carrier state for several months following recovery.

Symptoms are abdominal cramps, diarrhea, nausea, vomiting, chills, fever. It can be fatal, especially to the sick, infants, and the elderly.

food association
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.

Salmonella have also been isolated from many foods of plant origin( use of sewage as fertilizer or washing products with polluted water), and fish harvested from polluted water.

Different serotypes of salmonella are geographically distributed and vary in their pathogenecity.


In the U.S., SalmonellaTyphimurium has been considered the major causative agent of foodborne salmonellosis.

Foodborne salmonellosis from Salmonella Enteritidis has increased, mainly from contaminated shell eggs. The exact cause of predominance of SalmonellaEnteritidis is not 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.

prevention and control
Prevention and Control

Raw foods of animal origin that are heat treated before consumption can have Salmonella.

Many food processing industries have in-house Salmonella.

Control measures include proper cooking of foods(minimum to pasteurization temperature and time; 71.7C for 15 seconds and prompt cooling(3-4C or freezing if not used in 2 h).

Preventing cross-contamination of ready-to-eat food through cutting boards, equipment, utensils and hands.

Using proper sanitation and personal hygiene.

Properly reheating a food refrigerated for a long time.

detection methods
Detection Methods

The methods involve preenrichment of a sample in a nutrient broth, followed by selective enrichment, streaking on a selective-differential agar medium, and biochemical and serological confirmation.

Case Study

A group of people(24) attended a party, 6-57h later, 21 persons had gastroenteritis, with severe diarrhea, vomiting, fever and cramps. Twenty people needed medical help, of which 18 were hospitalized. SalmonellaEnteritidis was isolated from all 21 people(rectal swab). Epidemiological investigation revealed that the implicated food was homemade pasta dish consisting of one raw egg,


Ricotta cheese, cooked tomato and meat sauce.

They were mixed together in a pan and refrigerated overnight. Before serving, the preparation was baked for 30 min at 177C. Several attendees observed that the center of the dish was cold when served. SalmonellaEnteritidis was isolated from the leftover and from the unused eggs from the carton. SalmonellaEnteritidis was also isolated from laying hens at the poultry farm that supplied the eggs.


Several Campylobacter species can cause human gastroenteritis.

The most common causative agents are :

Campylobacter jejuni


Campylobacter coli


They are Gram-negative, motile, nonsporulating, rod-shaped bacteria. The cells are small, fragile, and spirally curved. The strains are microaerophilic and catalase and oxidase positive. Growth temperature ranges between 32-45C, with optimum 42C. They survive well under refrigeration and for months in the frozen state.



Campylobacter jejuni is an enteric organism, it has been isolated from feces of animals and birds.

Human carriers were found to shed the organisms in feces.

Fecal materials from poultry were found to contain more than one million cells/g.

Water, sewage, vegetables, and foods of animal origin are easily contaminated with campylobacter jejuni through feces.

Campylobacter jejunihas a thermolabile enterotoxin which cross –reacts with cholera toxin. 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.

disease and symptoms
Disease and Symptoms

The infective dose of campylobacteriosis is low(500 cells). Following ingestion, symptoms of the disease occur in 2-5 days and last for 2-3 days. Persons with no visible symptoms can shed the cells in feces for a long time.

The main symptoms are enteric and include abdominal cramps, diarrhea, nausea and vomiting. Other symptoms include fever, headache, and chills. In some cases bloody diarrhea has been reported.

food association1
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 Campylobacter jejuni.

The organism has been isolated frequently from raw meats(beef, lamb, pork, chicken, and turkey), milk, eggs, vegetables and mushrooms.

The use of animal feces as fertilizers was found to contaminate vegetables.


Proper sanitation reduces food load of the organism during production, processing and future handling.

Preventing consumption of raw foods of animal origin.

Heat-treatment of food.

Prevention of post-heat contamination.

Contamination of vegetables can be controlled by not using animal fertilizer and contaminated water to wash vegetables.

Adopting good personal hygiene to control contamination

By humans.