Foodborne Illnesses

Foodborne Illnesses Microorganisms enter the gastrointestinal

tract in association with ingested food and water.

  Two distinct processes that can initiate

disease through intestinal tract are:-

Food intoxication Food infection

1. Food intoxication Foodborne intoxication or food poisoning of microbial origins occurs from the ingestion of food

containing preformed toxin.  Due to production of toxin by the bacteria in the food. The bacteria usually do not grow in host.

Intoxication occur after food ingested.

Some general characteristics of food poisoning includes: 

a. Toxin is produced by a pathogen while growing in a food. 

b. A toxin can be heat labile or heat stable. 

c. Ingestion of food containing active toxin (not viable microbial cells) is necessary for poisoning.

 d. Symptoms generally occur quickly, as early as 30 minutes after ingestion.

 e. Symptoms differ with types of toxin; enterotoxins produce gastric symptoms and neurotoxins

produce neurological symptoms. 

f. Febrile symptom is not present. 

(a) Staphylococcal intoxication

Enterotoxigenic strains of S.aureus produce six different enterotoxin (A, B, C1, C2, D, and E) in many types of food. All these toxins vary in heat stability and the strength/potency.

Contaminated food do not have a distinct smell or taste unless hundreds of million present. Some of the foods that are frequently implicated are corned beef, salami, barbecued meat, salads, baking products.

Staphylococci toxins are enteric toxins and cause gastroenteritis. Symptoms such as nausea, vomiting, abdominal pain and diarrhea (1/3 of patient). Some secondary symptoms are sweating, chills, headache and dehydration. The disease lasts for about 1-2 days and is rarely fatal.

  The symptoms may occur within 2-4 hours after foods are ingested.

Characteristics of bacteria:Coccus, gram positive, non-motile, facultative anaerobe, the cells clump together like grapes. Grow well in foods containing 10% salt solution. Dissolve gelatine and produce heat stable toxin. Non capsule, non sporulating and non motile.

  If there is good intoxication by this microorganisms it is

possible that the toxin is present in food but the bacteria might have been destroyed during processing heating.

  Main source of contamination is man. Others are animal.

Personal hygiene of food handler is important. Avoid disease person from preparing food.

(b) Botulism 

Very rarely but once happen mortality rate is high. Botulism results from consumption of foods containing the toxin botulin produced by Clostridium botulinum.

  Spores of Clostridium botulinum is widely distributed in soil, sewage, mud,

sediments, lakes etc. Fruits and vegetables can be contaminated with spores from soil, fishes from water and sediments and various other foods from any of the above sources.

The botulin toxin are neurotoxic toxin produced disturb the peripheral nerve at the central nervous system. Following ingestion, the toxins are absorbed through the intestinal wall and reach the nerve cells, stopping the signal transfer and causing paralysis of involuntary muscle.

Neurological symptoms includes vomiting, ocular paresis (difficulty in moving eye), dilopia (double vision), paralysis of pharynx, sore throat, difficulty in swallowing, breathing, speaking, dryness of the mouth and paralysis of different involuntary muscles that spread to the lungs and heart. Death usually results from respiratory failure.

Characteristics of bacteria:The microorganisms is an anaerobe, gram positive, rod/club shape, motile, heat resistant and form single terminal spore (very resistant to heat). There are 6 strains (type A, B, C, D, E, and F)

  Cells are sensitive to low ph (<4.6), lower Aw (<0.93) and moderately

high salt (5.5%) therefore it does not produce toxin in acidic food. Only can produce toxin if pH is more than 4.6 and thus it is not a problem in acidic food.

Since it is a highly potent toxins, only a very small amount necessary to cause severe symptoms and even death (1 mg/kg body weight). Nevertheless, the toxin are relatively thermolabile i.e. easily inactivated by heat (80ºC for 30 min)

More than 90% of botulism cases are caused by homemade canned food due to under heating and leakage.

2. Food infection Ingestion of food containing pathogenic enteric

microorganisms. The microorganisms grow within the body and cause infection/poisoning.

  Generally establishment of infection requires a

relatively high infective dose.

The factors which influence the infection and infective dose are:

Organisms virulence Host resistance The buffering capacity of the food ingested

Some characteristics of foodborne infections include:a. Live cells of the enteric pathogens must be consumed through food.

b. The pathogens penetrate through the membrane and establish in the epithelial cells of the intestines, multiply and produce toxins.

c. Dose levels to cause infection vary greatly from 10 extremely virulent cells to about 10^5 cells or more.

d. Symptoms generally occur after 24 hours.

e. Enteric symptoms are local and due to enteric infection and the effect of toxins such as diarrhea, nausea, vomiting and fever.

f. Nonenteric symptoms occur when the pathogens or their toxins pass through the intestine and invade other intestinal organ and tissue.

(a) Salmonellosis Salmonellosis is a zoonosis i.e. disease transmissible between human

and animal. It is still the leading cause of foodborne disease.  The disease occur due to ingestion of Salmonella enteritidis at about

10^5-10^6 cells.

Characteristics of this bacteria are mesophilic, gram negative, nonsporulating, facultative anaerobe, motile rods. Gas formation when grow in glucose broth but not lactose, utilize citrate as carbon source, produce hydrogen sulphide, do not produce indole and negative for ureases. They are killed by pasteurization, sensitive to low pH and do not multiply at low Aw (<0.94)

  Salmonellae are natural inhabitants of the gastrointestinal tracts of

domestic animals. Human can be carriers following an infection and shed the pathogens through feces for a long time.

It can cause inflammation of the intestinal tract, abdominal cramps, diarrhea, nausea, vomiting, chills, fever and prostration. Feces may contain blood and in serious case, dehydration can occur.

Following ingestion, the pathogens invade mucosal layer and produce thermolabile toxin which results inflammation and accumulation of water in the intestine.

The ability of the pathogens to damage the cells is also attributed to the production of a thermostbale cytotoxic factor. Incubation period within 8-36 hours and the symptoms can last up to 3 days.

(b) Shigellosis  The genus Shigella contains four species: Shi. flexneri,

Shi. dysenteriae, Shi. bodyii, Shi. sonnei.

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.

The cells of the species are gram negative, non motile. Facultative anaerobes, rod shaped, catalase positive, oxidase and lactose negative and also fermenting sugars without gas.

The strains are believed to carry plasmid encoded invasive traits that enable them to invade epithelial mucosa of the small and large intestine.

Once engulfed by the epithelial cells. They are capable of producing an exotoxin that has the enterotoxigenic properties which is called as Shiga toxin.

  The infective dose is very low(10^1-10^3). Symptoms occur within 1-3

days after contaminated food ingested.

An infected person may shed the pathogens long after the symptoms have stopped.

The symptoms resulted from both the invasiveness of epithelial mucosa and the enterotoxin therefore abdominal pain, diarrhea often mixed with blood, mucus and pus, fever, chills and headache.