14- Food-borne pathogens Flashcards
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.
Top 10 causes of food-borne diseases?
- Leaving cooked foods at room temperature and/or storing foods in large containers in fridges
- Lapse of 12 h or more between preparation and consumption
- Colonized/infected persons handling food
- Inadequate reheating
- Improper hot holding
- Contaminated raw food/ingredients
- Foods from unsafe sources
- Improper cleaning of equipment
- Cross contamination – raw to cooked
- Inadequate cooking
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.
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.
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.
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.
