General Microbiology Lecture 11 - Food Microbiology Part 2A

In the US, most food borne illnesses are caused by 4 bacteria:

• Clostridium perfringens

• Campylobacter

• Staphylococcus aureus

• E. coli

Describe the characteristics of Clostridium perfringens.

• gram positive rod

• anaerobic

• spore forming bacterium

What does Clostridium perfringens cause?

nausea and diarrhea, usually does not cause fever

Why is Clostridium perfringens dangerous?

cells can divide every ten minutes, one of the fast growing bacterium, also produces toxins

What toxins and enzyme do Clostridium perfringens produce?

• alpha toxin (a phospholipase) that damages cell membranes

• pore forming toxin (perfrigolysin) that kills cells by disrupting membranes

• collagenase enzyme that degrades connective tissues

What are the characteristics of Campylobacter jejuni.

• gram negative

• S-shaped bacteria

• looks like spirochaete, but has polar flagellum

• microaerophilic

What does microaerophilic mean?

requires small amounts of oxygen

What is the most common cause of diarrhea disease in the US (20 cases per 100K people)?

Campylobacter jejuni

What does Campylobacter jejuni cause?

fever, bloody diarrhea, cramps

How is Campylobacter jejuni spread?

spread via poultry, dairy, seafood, untreated water, pets, takes very few cells to infect

True or false. There can be enough Campylobacter jejuni in a single drop of chicken juice to cause illness.

true

What does Campylobacter jejuni produce?

cytolethal distending toxin which prevents cell division and causes cell death of intestinal epithelial cells

Describe the characteristics of Escherichia coli.

• gram negative rod

• most strains are harmless or beneficial in the gut microbiome

• pathogenic strains can cause food poisoning

What strains of E. coli are of most concern?

shiga toxin producing strains (STEC)

What strain of E. coli is the most notorious?

E. coli 0157:H7

What are the symptoms of disease caused by E. coli?

fever, vomiting, diarrhea (often bloody), abdominal cramping

Why are shiga toxins from E. coli so dangerous?

Shiga toxins bind to eukaryotic ribosomes which block protein translation and leads to inflammation and cell death from cytokines

True or false. In severe cases of Shiga toxin producing strains of E. coli, the toxin can enter the bloodstream where it attacks the kidneys.

true

Describe the characteristics of Staphylococcus aureus

gram positive cocci

What does Staphylococcus aureus cause?

causes sudden nausea or diarrhea

Where is Staphylococcus aureus spread?

from contaminated deli meats, puddings, pastries, prepared sandwiches

What toxins do Staphylococcus aureus produce?

enterotoxins which are exotoxins that cause food poisoning

Why are the toxins produced by Staphylococcus aureus such an issue?

they are heat stable and cannot be denatured during cooking

Why are enterotoxins considered superantigens?

they cause excessive inflammation through overactivation of T cells and the overproduction of cytokines

Describe the characteristics of Salmonella enterica

• gram negative rod

• commonly found in the intestines of animals and humans

What does Salmonella enterica cause?

foodborne illness, especially through contaminated poultry, eggs or produce

What are the two most common serotype of Salmonella?

Typhimurium and Enteritidis

What are the symptoms of salmonella?

fever, diarrhea, abdominal cramps, vomiting

What happens when Salmonella enterica invades the human body?

invades intestinal epithelial cells which triggers inflammation

What does Salmonella enterica use to inject effector proteins into host cells

type III secretion system

What is Salmonella enterica considered and why?

facultative intercellular pathogen because it evades destruction by lysosomes and can enter bloodstream in severe cases which causes bacteremia