Experiment 4: Food Illnesses Caused by Staphylococci and Salmonellae

What is one of the most common forms of food poisoning?

Caused by enterotoxin-producing strains of Staphylococcus aureus.

• can enter food from food handlers and excrete exotocin into the food.

How else can food borne illnesses occur?

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

Salmonella infections

• endotoxins releases from LPS membrane from the organism which grows on the intestinal tract after being ingested with contaminated food.

Why is an enrichment step needed for salmonella sample?

Because only a small # of salmonella are found in the food product.

Food poising outbreaks

only one organism is the etiologic agent

• responsible for causing a disease or condition

What selective property does Staphyloccocus 110 agar have and how does it help in isolating S. aureus?

highly selective due to its 7.5% sodium chloride concentration

• inhibits the growth of most Gram-negative and non-staphylococcal bacteria

• allows S. aureus to grow while suppressing unwanted competitors

What is the purpose of BHI (brain-heart infusion) broth in this experiment?

Salmonella wont grow on selective Macconkey agar so BHI provides an optimal environment for them to recover, repair, and multiply so we can see them.