14- Food-borne pathogens Flashcards Preview

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Flashcards in 14- Food-borne pathogens Deck (6):
1

What are food-borne pathogens? Food poisoning? Food infection?

• Many diseases can be transmiled by means of foods. Any food that is handled, processed or stored improperly may be a public health hazard.
• Many fresh foods are contaminated with pathogens, but the initial population is
usually too low to cause illness in a healthy individual. Ex.: raw milk.
• The subsequent abuse of the food (e.g. storage at warm temperature) permits the
growth of pathogens to a level sufficient to cause illness.

• Food poisoning/intoxication: caused by microbial toxins in food. Symptoms appear quickly.

• Food infection: organisms are ingested with the food and multiply in the host. Symptoms take longer to develop. Illness may be due to tissue invasion, production of toxins or both.

2

Top 10 causes of food-borne diseases?

1. Leaving cooked foods at room temperature and/or storing foods in large containers in fridges

2. Lapse of 12 h or more between preparation and consumption

3. Colonized/infected persons handling food

4. Inadequate reheating

5. Improper hot holding

6. Contaminated raw food/ingredients

7. Foods from unsafe sources

8. Improper cleaning of equipment

9. Cross contamination – raw to cooked

10. Inadequate cooking

3

Explain botulism

• Food poisoning, ingestion of the neurotoxin produced by Clostridium botulinum.
• 10% mortality, causes flaccid paralysis, respiratory or cardiac failure.
Symptoms: difficulty swallowing, double vision,
breathing difficulty, paralysis. 1-2 days.

• Anaerobe that produces spores, risk factors:
– Home canning, insufficient heat to kill the spores.
– Processed foods that are not reheated (non-acid canned vegetables, sliced meats)
– Spores germinate, growth, toxin is produced

Toxin is destroyed by heating (80°C, 10min). Properly cooked foods are safe to eat; it destroys the toxin, not the
organisms.

4

Explain Staphylococcal food poisoning

• Most common form of food poisoning, accounts for 40% of food poisoning cases.

• Due to an enterotoxin (SE) produced by some strains of Staphylococcus aureus
(enterotoxigenic strains). The toxin is relatively heat-stable (30 min at 100°C, 16h at 60°C).
• 20-30% of humans are colonized by S. aureus (skin and upper respiratory tract). It
is easily transferred to food where it can grow and produce the toxin. Symptoms appear quickly (1-6 h): nausea, vomiting, diarrhea.

• Associated with food prepared in large quantities and then, left at room
temperature (banquet, picnic, airline meals). Halotolerant, can grow on salted sausage, etc.
• Keep cold food cold and hot food hot. Adequate sanitation/hygiene.

5

Explain Salmonella enterica

More than 2000 serovars. (Typhimurium, Enteritidis, Typhi). Only a fraction is isolated from human infections.
Infection of mammals, birds and reptiles.

• Food infection, Salmonella grows in the intestinal tract (salmonellosis); uses two
injectisome systems. Most frequent serovars are Enteritidis and Typhimurium.

• 10'5-10'8 organisms are required to cause disease. Salmonella must usually multiply in the food before the food is eaten.

• Symptoms are caused by the invasion and destruction of the intestinal epithelium.
• Associated with uncooked or slightly cooked foods, or cooked foods that are contaminated after cooking (cross contamination).
• Cooking kills Salmonella enterica. Good sanitation practices are important to minimize the chance of cross contamination.

6

Explain Escherichia coli O157:H7

• Fecal coliform BUT DOES NOT GROW AT 44.5°C; escape detection by standard fecal coliform methods.

• Enterohemorrhagic E. coli (EHEC). Effective dose is < 100 microorganisms. Cooking kills the microorganism.

• Food infection, attaches to the intestinal mucosa and produces an AB-type exotoxin: Shiga-like toxin that inhibits protein synthesis.

• The toxin damages the underlying tissues -> causes bloody diarrhea (hemorrhagic
colitis)
• The toxin travels through the blood stream and destroys cells in the kidney -> causes hemolytic uremic syndrome (HUS), can result in acute renal failure and death.