Experiment 4 - Food Illness Caused By Staphylococci and Salmonellae

How are the categories of food illness based upon?

Based on what causes the symptoms

What are the two categories of food illness?

1. Intoxication caused by ingesting microbial exotoxins

2. Infection caused by ingesting pathogenic organisms.

What is the most common forms of food poisoning?

Enterotoxin-producing strains of Staphylococcus

How do these organism enter food?

From many sources such as food-handlers and excrete a heat stable exotoxin into the food products.

What is another disease process?

Ingestion of pathogenic microorganisms that grow in the intestinal tract and produce toxic substances

How are microbes killed and exotoxins destroyed?

By cooking food thoroughly.

What is Salmonella the cause of?

Illness in eggs, poultry, and cross-contaminated raw ground meats.

What is Staphylococcus the cause of?

Cause in undercooked meats, especially ground hamburger meat

What does Salmonella infection involve?

The liberation of endotoxins (LPS in outer membrane) from the organism which has grown in the intestinal tract after being ingested with contaminated food

How can Staphylococcus aureus enter food?

From many sources including animals, food handlers, and unsterile processing.

What does Staphylococcus aureus do?

Produces heat stable exotoxins, which it secretes and can remain in food even when the cells themselves are killed off.

How can we destabilize the toxin from Staphylococcus aureus?

Food must be heated at relatively high temperature for a period and handled hygienically afterward.

How often does Staphylococcus aureus occur?

Intoxication occurs most often in foods that are not regularly heated like potato salads or sliced meat

How fast do symptoms of Staphylococcus aureus intoxication occur?

Set in quickly and are relatively short lived except for C. botulinum toxins which are often fatal.

How many Staphylococci are necessary to produce food poisoning?

Large numbers and some degree of quantization

How can Salmonella sp. enter food?

Requires ingesting viable cells that can survive the conditions of the digestive system.

What is Salmonella sp. infection the result of?

Undercooked food and unhygienic handling

How fast do symptoms of Salmonella sp. intoxication occur?

Do not set in until an extensive lag period so it can be several hours to days before infection sets in.

How is Salmonella sp. pathogenic?

Via its endotoxins, LPS within the outer membrane, that damage intestinal cells

Is Salmonella sp. infection life threatening?

Not often life threatening outside of outbreaks involving highly pathogenic strains, usually traced back to contaminated ground meats

How much Salmonella is necessary to produce food poisoning?

Often only small numbers are found in a food product

How can we detect Salmonella sp. ?

With an enrichment step

How can we detect coagulation of Staphylococcus?

By slanting the test tubes slightly since there is a strong relationship between strains capable of producing the enzyme coagulase and the exotoxin

What does Salmonella sp. look like? What is its property?

Transparent to white or very light pink in colour. They do not ferment lactose.

How can Salmonella isolates be further screened?

By using additional biochemical and serological tests.