BB5MOP Week 19

How do food borne illnesses spread?

During food preparation, cooking processes, animals and already contaminated foods.

What is the Kauffman-White classification?

Giving each salmonella strain its own label based on their antigens.

What antigens are looked at in the Kauffman-White classification process?

Flagella with the H antigens and somatic with the O antigens in the LPS.

Where is the typhimurium strain of salmonella found?

Wild animals like chicken.

Where do e. coli strains live and why do they live there?

Warm blooded animals, cause the infection to have a shorter incubation time.

What are the three steps that Salmonella uses to cause infection?

Colonise, Evade and Damage (similar to S. aureus).

What is the colonization process in S. typhimurium infection?

Salmonella establish themselves by passing through epithelial cells and M cells within the gut.

What is the evasion process in S. typhimurium infection?

Hijacks the phagocytes to evade detection and live within macrophages and multiply.

What is the damage process in S. typhimurium infection?

Releasing proteins that cause inflammation in the gut causing gastroenteritis.

Where are salmonella pathogenicity islands found (SPIs)?

Found in the DNA of salmonella

Why are SPI 1 and SPI 2 important?

They work together to create the type 3 secretion system (T3SS).

What is the type 3 secretion system (T3SS)?

Allows salmonella to inject its own proteins into human cell DNA and manipulate it.

What does SPI 1 do?

Gets activated during initial attachment of pathogen.

What does SPI 2 do?

Gets activated when salmonella is engulfed by phagocytes.

What does SPI 3 do?

Helps pathogen to stay alive in phagocytes.

What does SPI 4 do?

Involved in sticking to the host cells.

What does SPI 5 do?

Prevents cells from undergoing apoptosis, so the salmonella remains alive while inside the host cell.

Describe SPI action.

1. Adhesion, SPI 4 helps stick the pathogen to the cell lining.

2. Triggers a cascade activating SPI regions.

3. Changing cytoskeleton of the cell making it easier for the pathogen to enter, picked up by dendritic cells.

4. Inside, pathogen is enclosed in a salmonella containing vacuole (SCV) and replicates inside and then released.

Describe how E. coli O157:H7 causes infection.

1. Attaches to intestines, using fimbriae and targets enterocytes in the lining of the intestines.

2. Bacteria injects TIR (translocated intimin receptor) into human cell, causing cell to make TIR receptor.

3. Bacteria binds to TIR receptor it created on host cell with strong attachment.

4. Releases Shiga toxins that bind to GB3 receptor and shuts down cells ability to make proteins.

What happens as a result of the human cells not making proteins?

Cell will not function properly and start to die, causing bloody diarrhoea.

How does the E. coli O157:H7 strain become systemic and what cells does it attack?

Shiga toxins go into bloodstream spreading throughout the body, attacking RBCs, platelets, kidney and brain.

What disease does the E. coli O157:H7 strain cause?

Haemolytic uremic syndrome (HUS)

How does S. typhimurium appear on blood agar, MAC agar and XLD agar?

1. Blood agar - white colonies, gamma haemolytic.

2. MAC - appears yellow, non-lactose fermenting.

3. XLD - black colonies, ferments xylose and lysine.

What are the biochemical test results of S. typhimurium in gram staining, catalase test, oxidase test and indoles test?

1. Gram negative, bacilli

2. Catalase - positive

3. Oxidase - negative

4. Indole - negative

How does E. coli appear on blood agar, MAC agar and XLD agar?

1. Blood agar - sheen colonies, beta haemolytic.

2. MAC - appear pink, lactose fermenting.

3. XLD - yellow colonies, lactose/lysine fermenting.

What are the biochemical test results of E. coli in gram staining, catalase test, oxidase test and indoles test?

1. Gram negative, bacilli

2. Catalase - positive

3. Oxidase - negative

4. Indole - positive

What is the difference between E. coli and E. coli O157:H7 on SMAC agar?

1. E. coli ferments sorbitol, pink/red colonies

2. O157:H7 cannot ferment sorbitol, ferments lactose, has yellow colonies.

What is the gram stain and shape of Bacillus species?

Gram positive, bacilli that form spores.

What are the two forms of infection that Bacillus cereus causes?

Emetic and Diarrheal forms

Describe the emetic form of Bacillus cereus infection.

1. Production of cereulide toxin, which goes to the digestive system and intestines binding to receptors.

2. Disrupts mitochondria function and balance of ions, increases inflammation in the kidneys.

3. Lasts 30 to 6 hours, nausea and vomiting.

What is the diarrheal form of Bacillus cereus infection?

Caused by bacteria itself growing in the gut producing enterotoxins, lasts 6 to 15 hours.

What are the three types of diarrheal bacilli enterotoxins?

1. Non-haemolytic enterotoxin (Nhe)

2. Haemolysin BL (Hbl)

3. Cytotoxin K (CytK)

Describe the non-haemolytic enterotoxin (Nhe) process of B. cereus infection.

1. Made up of three components: Nhe A, Nhe B and Nhe C.

2. Work together to form a pore in the membrane of intestinal cells, cells die via apoptosis.

Describe the haemolysin BL (Hbl) process of B. cereus infection.

1. Made up of three components: Hbl-B, Hbl-L1 and Hbl-L2.

2. Assemble to form pore in the cell membrane of intestinal cells.

Describe the cytotoxin K (CytK) process of B. cereus infection.

1. Causes cell damage and disrupts cell membrane ion balance.

2. Immune system activated by CytK causing inflammation and cell death.

How are Bacillus species identified?

Spore staining

What is the difference between B. cereus and B. subtilis on PEMBA agar?

1. B. cereus - negative blue colonies, no mannitol fermentation so there is lecithinase production.

2. B. subtilis - positive yellow/green colonies, mannitol fermentation, so there is no lecithinase production.

What is the difference between B. cereus and B. anthracis on blood agar?

1. B. cereus has golden colonies, beta haemolytic.

2. B. anthracis has white colonies, gamma haemolytic.

What is the difference between B. cereus and B. anthracis in the motility test?

1. B. cereus - spreads out, positive for motility.

2. B. anthracis - does not spread out, negative for motility.

What is the difference between B. cereus and B. anthracis in the penicillin test?

1. B. cereus - resistant to penicillin.

2. B. anthracis - sensitive to penicillin.