Foodborne pathogens

Hippocrates in 460 BC reported that there are as strong connection between food consumed and human illness.

What is a pathogen? A pathogen is defined as an organism causing disease to its host, with the severity of the disease symptoms referred to as virulence. Pathogens are taxonomically widely diverse and comprise viruses and bacteria as well as unicellular and multicellular eukaryotes.

A pathogen brings disease to its host. Another name for a pathogen is an infectious agent, as they cause infections. As with any organism, pathogens prioritize survival and reproduction.

Foodborne pathogens are biological agents that can cause a foodborne illness event. Foodborne pathogens are a concern for both public health officials and the food and dairy industries.

There are five main types of pathogens: Bacteria, Viruses, Fungi, Protists, Parasitic worms

Common foodborne pathogens including:
*Campylobacter
*Clostridium botulinum
*E. coli O157:H7
*Listeria monocytogenes
*Norovirus
*Salmonella
*Staphylococcus aureus
*Shigella
*Toxoplasma gondii
*Vibrio vulnificus

Campylobacter sp. (mostly associated with raw or undercooked poultry) is the major foodborne pathogen in the U.S. food supply, causing more than two million infections per year, while Salmonella, mostly found in meat, poultry, and eggs, is responsible for more than one million cases of food poisoning.

Foodborne illness occurs when a pathogen is ingested with food and establishes itself (and usually multiplies) in the human host, or when a toxigenic pathogen establishes itself in a food product and produces a toxin, which is then ingested by the human host.

In recent times, a significant number of people have died due to foodborne diseases, and such pathogens are a priority and a critical health issue all over the world. It was reported that roughly one of every six Americans in the U.S.A. get sick, the number of hospitalized patients is 128,000, and 3000 people die due to foodborne diseases annually.

The factors contributing to the emergence of foodborne diseases are changes in human demographics and behavior, technology and industry, and international travel and commerce; microbial adaptation; economic development and land use; and the breakdown of public health measures.
Foodborne pathogens

Food related illnesses

Foodborne illness is a common, costly, sometimes life threatening—yet largely preventable—public health problem. Food borne diseases (FBD) are acute illnesses associated with the recent consumption of food. The food involved is usually contaminated with a disease pathogen or toxicant.

The CDC estimates that about 90% of all foodborne illness in United States is caused by the following seven (7) pathogens: Norovirus, Salmonella, Clostridium perfrigens, Campylobacter, Listeria, E. coli 0157:H7 and Toxoplasma.

What are the symptoms? Symptoms range from relatively mild discomfort to very serious, life-threatening illness. While not all gastroenteritis is foodborne, and not all foodborne diseases cause gastroenteritis, food does represent an important vehicle for pathogens of substantial public health significance.

Food borne diseases are classified into:
1. Food borne infections and
2. Food borne intoxications
Food related illnesses

Strain of Escherichia coli O157:H7

Although most kinds of E. coli bacteria do not cause disease in humans, those that are pathogenic are a significant threat to public health, especially relating to food safety.

The most common and notorious of these pathogenic bacteria are E. coli O17:H7, which part of a category call enterohemorrhagic E. coli (EHEC).

Escherichia coli O157:H7 was first identified as a human pathogenic in 1982. A rare but dangerous type of E. coli, the strain O157:H7 is now a major public health problem worldwide.

The main method of identifying pathogenic strains of E coli has been stereotyping base on specific markers found on the bacterial cell surface, namely the O, H and K antigens. The “O” antigen of E. coliO157:H7 was the 157th cell surface lipopolysaccharide or somatic antigen, to be identified; the ”H” antigen was the seven flagellar antigen identified.

The major reservoir of E. coli O157:H7 are ruminant animal, particularly cattle. E. coli O157:H7 has also been isolate from sheep, deer, and goats. E. O157:H7 was identified as the cause of two outbreaks of hemorrhagic colitis that occurred in 1982 and were associated with undercooked ground beef.
Strain of Escherichia coli O157:H7

Vibrio parahaemolyticus

One of the common bacterial foodborne pathogens is Vibrio parahaemolyticus. It is the most common seafood pathogen and along with other members of the genus.

Vibrio parahaemolyticus is a halophilic marine bacterium first isolated from Shirasu, semi-dried juvenile sardine, implicated in an outbreak.

The first food poisoning case due to Vibrio parahaemolyticus reported outside Japan was from the East Coast of the United States in 1971.

Vibrio parahaemolyticus gastroenteritis is generally self limiting with diarrhea, abdominal cramps, nausea, vomiting, fever and chills being common signs and symptoms of this disease.

Vibrio parahaemolyticus is typically present in seafoods and occurs only sporadically on other foods that have been exposed to salt, such as salt-preserved vegetables.

In North America and Europe most outbreaks of Vibrio parahaemolyticus-induced gastroenteritis have been due to the consumption of raw mollusks (oysters and clams) or cooked crustaceans (shrimp, crab and boosters).

The increase of the outbreaks incidence may be attributed to many factors such as warmer water temperatures or an increase in raw shellfish consumption. Vibrio parahaemolyticus can be isolated from coastal waters when the water temperature is 15 °C or above. The organism can only be detected in sediment with the temperature is below 15 °C.
Vibrio parahaemolyticus

Food irradiation reduces biological food contamination

Food irradiation reduces biological food contamination and related foodborne illness.

With the increase of some food borne infectious diseases in many countries, irradiation has been proposed as a procedure which could eliminate microbial pathogen contamination of food at the processor level and thus allow the delivery to the consumer of a safer product.

Food irradiation has been approved for use in the United States in selected foods since 1963. 

Electromagnetic radiation suitable for food irradiation may be electrons, X-rays or gamma ray. Ionizing radiation passes through the food and destroys harmful bacteria and other organisms.

Irradiation could reduce spoilage ro the need for fungicides for fruits, and increase the safety of meats.

It is also effective for seafood, eggs, precooked meats and produce. It is safe, proven process that has many useful applications.

The potential for using radiation as a way of destroying pathogens in food has been known for more than a century.
Food irradiation reduces biological food contamination

Toxoplasma gondii

Toxoplasma gondii is a protozoan parasite which can be transmitted by fecal-oral contamination. Cats are the original hosts for this protozoa. They excrete microscopic in active forms of this protozoa in their feces. Farm animals (notably sheep and pigs) become infected by consuming feed and water contaminated by barn cats’ fecal material.

Active forms of this parasite then multiply with the farm animals and encyst themselves in the brain, heart muscle, other skeletal muscle, and liver. The cysts are microscopic and can exists as long as the farm animal lives.

When these animals are slaughtered to provide meat, the raw meat contains the cysts which can then infected humans if it is eaten raw or not heated sufficiently to inactive various forms of this parasite. About 30% of all fresh pork is infected and is the main meat source of Toxoplasma gondii in the United Sates.

If cutting and grinding equipment is not thoroughly washed and sanitized, other raw meats such as ground beef can also become contaminated. About 5% of the ground beef sold in supermarket contains some pork because the grinding equipment is not properly cleaned between grinding operations. Cysts of this protozoa are also found in wild game meats such as elk, moose, and venison.

Symptoms of the disease in humans are fever, muscle aches, headaches, loss of appetite and sore throat. Other symptoms will appear, depending upon the internal organs involved. In pregnant women, these parasites can be carried by way of the placenta to fetal tissue. If fetuses are infected, spontaneous abortions may occur. Most infected infants show no obvious symptoms at birth, but will show signs of eye damage and mental retardation later in life.

It is estimated that there are over 3,300 cases of congenital Toxoplasmosis each year resulting in 450 deaths of infants and young children. Other surviving infected children are mentally retarded as a result of this parasitic infection.
Toxoplasma gondii

Salmonella Association with Foods

Salmonella Association with Foods
The bulk of human salmonellosis is clearly related directly to man’s association with animals, both wild and domestics. Salmonella are host adapted; however most Salmonella are not host adapted. Although any Salmonella is a potential pathogen for humans, most food borne salmonellosis is caused by non-host adapted serotypes.

Improper cooling, inadequate cooking of thermal processing, ingestion of contaminated raw products and cross contamination were frequently identified as contributing factors in the implicated foods. Raw foods of animal origin are the major sources of salmonellae in kitchens of restaurants, institutions and homes. Salmonella may survive in these foods as a result of improper cooking, more commonly, cross contamination of foods after cooking is the source of Salmonella. Foodservice workers or in home preparers may transfer salmonellae from raw products to cooked or other uncontaminated foods as a result of not washing between handling of these foods. Salmonella can also be transferred from contaminated raw foods to equipment surfaces e.g., knives cutting boards, counter tops, etc, and then from equipment to previous uncontaminated foods. Once contamination occurs, the situation may further complicated by insufficient storage of the product before serving. Contaminated foods are sometimes kept at room temperature, improperly refrigerated, or held in warmers within the growth range for salmonellae.

Although responsible for fewer outbreaks, contamination of foods by infected workers cannot be ignored as a cause of foodborne salmonellosis. Improper hygiene practices by these individuals may lead to either contamination of foods or direct person-to-person contamination. Historically egg-products were a significant source of human salmonellosis in the United States but mandatory pasteurization of egg products has been responsible for greatly reducing eggs as an important cause of salmonellosis.
Salmonella Association with Foods

Shigella as a Pathogen

Shigella as a Pathogen
Shigellosis, or bacillary dysentery, as it is commonly known, is caused by bacteria of the genus Shigella (S. dysenteriae, S. flexneri, S. boydii and S. sonnei). The normal habitat for Shigellae is the intestinal tract of humans and other primates. They are rarely found in other animals. The main source of Shigellae involved in outbreaks is asymptomatic carriers or persons recovering from disease. Shigellae may persist in the intestinal tract for month.

Symptoms of shigellosis, after an incubation period of 1-7 days (usually less than 4 days), include diarrhea, abdominal pain, fever, and vomiting. The severity of the disease may vary from very mild to severe diarrhea with bloody stools, mucus secretion, and dehydration. Generally foodborne shigellosis is characterized by a high attack rate common source epidemiology, and short incubation periods of 7 – 36 hours. Symptoms usually persist for 3 – 14 days. Frequently, an asymptomatic carrier state may develop during convalescence, lasting from a few days to several months. Human volunteer studies indicate that ingestion of as few as 1 – 100 organisms can induce illness.

The disease is caused by invasion of the intestinal mucosa. An enterotoxin, classically referred to a Shiga toxin, may be produced by S. dysenteriae and possibly by S. flexneri.
Shigella as a Pathogen

Salmonella: significance as a pathogen

Salmonella: significance as a pathogen
Two clinical entities cause by Salmonella are recognized: enteric fever (a severe, life threatening illness) and the more common food poisoning syndrome. In both cases, the organisms enter the body via oral route.

Enteric fever, commonly referred to as typhoid fever, is primarily caused by the one species Salmonella typhi, but other salmonella are potentially capable of producing this syndrome. The symptoms of enteric fever are generally not elicited through the intestinal tract, although the route of entry into the body is primarily oral. However, a short period of vomiting and diarrhea sometimes occurs in the first day or two in typhoid fever. The onset times vary considerably between typhoid and paratyphoid enteric fevers. Onset times for typhoid are usually 8 – 15 days, seldom as short as 30 – 35 days: while onset time for paratyphoid fever tends to be shorter, and may be so short as to suggest food poisoning. The usual symptoms of salmonellosis are headache, malaise, anorexia, and congestion of the mucous membranes, especially of the upper respiratory tract. Bacteremia generally occurs on the first week of illness.

The food poisoning syndrome is characterized by a self-limiting acute gastroenteritis. Contaminated food or water is the usual, but not the only, vehicle. The incubation period varies from 6 to 48 hours and generally falls within a range of 12 – 36 hrs. Variation in the incubation time may be attributed to the size of the infecting dose, the virulence (degree of pathogenicity) of the organisms, the susceptibility of the host, and the physicochemical composition of the transmitting food. Symptoms include diarrhea, abdominal cramps, vomiting and fever which generally last from 1 - 7 days. However, the organisms may be excreted in the feces for many weeks after symptoms subside.

Salmonellosis may be confused clinically with staphylococcal intoxications, but there are important distinctions. Salmonella has a longer incubation period than staphylococci and is usually accompanied by fever, which is absent in staphylococcal intoxication. And, unlike Salmonella food poisoning, the acute symptoms of staphylococcal food poisoning normally disappear within 24 hrs.

In some case, the gastroenteritis may be followed by extraintestinal invasion resulting in enteric fever, which is more, likely to occur in the very young, the aged and debilitated patients.
Salmonella: significance as a pathogen

Bacillus cereus: Toxin and Spore Producing Bacteria

Bacillus cereus: Toxin and Spore Producing Bacteria
Bacillus cereus, a spore forming microorganisms, is present in soil and can be isolated from a wide variety of vegetation and food. It has been found to be present in the intestinal tract of 10 percent of healthy adults. It is often present in dairy products, meats, spices, dried products, and cereals (particularly rice). Food products implicated in this type of illness have included: cereal dishes containing corn and cornstarch, potatoes, vegetables, meat product, puddings, soups, sauces, fried rice, and ilk and dairy products. Vegetative cells of Bacillus cereus are destroyed by most cooking processes, but heat resistant spores survive.

When cooked food containing spores of Bacillus cereus is cooled and allowed to remain at warm kitchen temperatures, the spores germinate to form viable cells. The population of cells increases in the food. Illness results form ingestion of food containing a large number of cells of Bacillus cereus, that then produce toxin in intestine.
There are two types of Bacillus cereus foodborne illness:

Diarrheal illness
The Diarrheal illness is most often associated with meat product, soups, potatoes and starchy vegetables, puddings, and sauces. The onset of symptoms occurs 8 to 16 hours after ingestion of food containing the microorganisms or toxin. Symptoms include abdominal pain and diarrhea and occasionally, nausea and vomiting.

Emetic illness
The emetic form of illness may result in diarrhea and abdominal cramps, but is most often characterized by nausea and vomiting. Its onset occurs 1 to 5 hours after ingestion. The duration of illness is from 6 to 24 hours. These types of illness is most often associated with the rice dishes and pasta products that were held at improper temperatures and slow cooling of large quantities of foods.

Critical problems in today’s food supply that lead to illness caused by Bacillus cereus are:

• Holding cooked foods at room temperatures for along periods of time prior to reheating or serving them.

• Cooling foods at temperatures that allow the germination and growth of cells of Bacillus cereus.

• Failure of foodservice personnel to use good personal hygiene when working on foodservice facilities. People can be carriers of this microorganism. If they do not wash their hands and under their fingernails after defecating, they can transmit this pathogen to anything they touch or handle.

Bacillus cereus: Toxin and Spore Producing Bacteria