Food borne bacterial gastroenteritis caused by Salmonella, E. coli and Vibrio spp

2. E. coli gastroenteritis:

• E. coli is generally regarded as normal flora of gastrointestinal tract of animal but several strain of E. coli cause diarrheal disease which are usually foodborne.
• Several outbreaks of E. coli gastroenteritis have been reported so far including recently occurring gastroenteritis outbreak in some European countries.

Etiological agent:

• Natural habitat of E. coli is gastrointestinal tract of animal and it is excreted in stool.
• Therefore, presence of sufficient number of E. coli in food indicates stool contamination E. coli strain causing gastroenteritis are divided into 5 groups:
  • Enteropathogenic E. coli (EPEC)
  • Enterotoxigenic E. coli (ETEC)
  • Enterohaemorrhagic E. coli (EIEC)
  • Facultative enteropathogenic E. coli (FEPEC)

Food involved in E. coli gastroenteritis::

• Outbreak of E. coli gastroenteritis usually associated with cheese and vegetable product but other food like creamed fish are also found associated.

Pathogenesis and symptoms of E. coli gastroenteritis::

• E. coli gastroenteritis is caused by ingestion of about (10⁶-10¹⁰) viable bacterial cells.
• After ingestion, they attach to epithelium of intestine by pili or fimbriae.
• Gastroenteritis caused by E. coli is characterized by non bloody diarrhea.
• Diarrhea is watery and is similar to that caused by Vibrio cholera.
• Pathogenesis and detailed symptoms differ with type of strain as given below:
• EPEC strain attach to the surface of intestinal epithelium by colonization factor antigen (CFA) type of pili and produce two types of toxin i.e. heat labile toxin and heat stable toxin.
• Heat labile toxin enter into intestinal cell and increase the level of CAMP.
• Similarly, heat stable toxin enter into intestinal cell and increase the level of CGMP.
• Increased level of CAMP and CGMP inhibit absorption of Na⁺ ion by epithelial from the intestinal lumen and at the same time it causes secretion of more water and Cl^– ion from the epithelial cell into intestinal lumen.
• Therefore, ETEC strain also causes watery diarrhea. ETEC strain is associated with travellers diarrhea.
• ETEC strain is represented by E. coli O₁₅₇H₇.
• They produce two types of toxin i.e. shiga like toxin 1^st (SLT-I) or (verotoxin or verocytotoxin) and shiga like toxin 2^nd (SLT-II).
• SLT -I and SLT-II are cytotoxin and kill the cell by inhibiting protein synthesis.
• EHEC causes hemorrhagic colitis which is a serious type of diarrhea.
• It also causes hemolytic uremic syndrome (HUS) which is characterized by renal failure.
• EIEC strain causes diarrhea by invading through the intestinal epithelium, the mechanism is similar to the Shigelosis.

Treatment of E. coli gastroenteritis::

• Treatment of diarrhea caused by E. coli is giving salt solution to counteract loss of water and electrolyte during diarrhea.

Prevention and control E. coli gastroenteritis:

• Main source of E. coli is stool of human beings and other animals.
• Therefore, sanitary practice is important to prevent contamination of food by stool.

3. Gastroenteritis caused by Vibrio spp.

• The genus vibrio consist of at least 28 species and four species are often associated with food borne gastroenteritis.
• They include:
  • Vibrio parahaemolyticus
  • Vibrio vulnificus
  • Vibrio alginolyticus
  • Vibrio cholerae
• Of them, Vibrio parahaemolyticus is most commonly associated with food borne gastroenteritis.

Vibrio parahaemolyticus gastroenteritis:

• Vibrio parahaemolyticus is halophilic bacteria and causes acute gastroenteritis after ingestion of sea food like raw fish and shell fish.
• It is the most common type of food borne gastroenteritis caused by vibrio species.
• Most other bacterial food poisoning are associated with wide variety of food, but this food poisoning is associated only with sea food.
• If any other foods are found associated it indicates direct mixing of sea food with that food.
• Etiological agent:
  • Vibrio parahaemolyticus is halophilic and grow in the range of 1-8% NaCl, but maximum growth occurs at 2-4% NaCl.
  • Range of temperature for growth is 4-44^oC with optimum pH being 7.6-8.6.
  • It is heat sensitive.
  • Most strain produce thermostable direct hemolysis (TDH) and some produce heat labile hemolysis and other produce both.
  • Some strain also produces thermostable related hemolysis (TRH), which is an important virulence factor.
  • This bacteria attach to intestinal epithelium by hemagglutinin. Pilli also helps in attachment.
• Food involved :
  • Natural habitat of this bacteria is sea water.
  • Therefore, food poisoning by this bacteria is mainly associated with sea food like fish, shell fish etc.
  • In rare cases, other foods are also found associated.
  • If this occurs, it indicates direct-mixing of sea food with other food.
• Disease symptoms:
  • Incubation period ranges from 2-48hrs.
  • Abdominal pain and diarrhea are common symptoms.
  • During diarrhea, watery stool with blood and mucus appear.
  • Nausea, vomiting, mild fever and headache also occurs.
  • The disease is self-limiting and recovery occurs within 2-5 days.
• Treatment:
  • The disease is self-limiting and requires no specific treatment.
  • In extreme cases salt solution is given to counteract loss of water and electrolyte during diarrhea.
• Prevention and control:
  • Natural habitat of this bacteria is sea water.
  • Therefore, sea water should not be used for processing of food, that prevent contamination.
  • Microorganisms present in contaminated food can be prevented from growing by sufficiently refrigerating during storage.
  • Finally, bacteria present in food can be killed by heating the food just before eating.

Vibrio cholerae gastroenteritis:

• Vibrio cholerae causes epidemic cholera which is a serious type of gastroenteritis.
• Although cholera is usually waterborne disease, some outbreaks are also found associated with ingestion of contaminated food.
• It is associated with ingestion of sea food.
• Usually Vibrio cholerae strain O₁ cause food borne gastroenteritis but several outbreaks are also found associated with non O₁ strain.
• Food involved:
  • Cholera is usually waterborne, sometimes is caused by ingestion of contaminated sea food.
• Etiological agent:
  • Usually Vibrio cholerae strain O₁ causes food borne cholera but some outbreaks are found to be associated with non O₁ strain.
• Pathogenesis:
  • It is a non-invasive type of infection and microorganisms do not penetrate through intestinal epithelium.
  • After ingestion, Vibrio cholerae multiply in intestine and produce enterotoxin (cholera toxin).
  • When vehicle is water, person with normal activity becomes infected only by ingestion 10¹⁰ or more bacterial cell.
  • But if vehicle is food, just 10²-10⁴ bacterial cells are sufficient to cause cholera.
  • It is because buffering capacity of food protect the ingested bacteria from stomach acidity.
  • After production, cholera toxin enters into the intestinal epithelial cell and increases the level of CAMP in cell.
  • Increased level of CAMP inhibits absorption of Na⁺ and Cl^– ion from intestinal lumen by intestinal epithelial cell.
  • At the same time, it causes hypersecretion of water and ions from intestinal epithelial cell into intestinal lumen.
  • This causes loss of water and electrolyte and produces diarrhea.
• Symptoms:
  • Incubation period is usually 1-4 days depending on amount of organism ingested.
  • Nausea, vomiting, diarrhea and abdominal pain occur very suddenly.
  • Stool resemble rice water in appearance which contains mucus epithelial cells and large number of Vibrio cholerae.
• Treatment:
  • Give salt solution to counteract loss of water and electrolyte during diarrhea.Give tetracycline orally, that inhibits Vibrio spp. in intestine.

other Vibrio species

1. Vibrio vulnificus:
   • This organism is found in sea water and sea food.
   • It is highly invasive and causes septicemia. It also produces hemolysin and cytotoxin.
2. Vibrio alginolyticus:
   • Its natural habitat is sea water. In human being, it causes soft tissue and ear infection.

Food borne bacterial gastroenteritis caused by Salmonella, E. coli and Vibrio spp