Week 4 - Gram Negative Bacilli

Question 1

Pseudomonas aeroginosa can form a ___________ in cystic fibrosis patients

Answer 1

biofilm

Question 2

E. coli 0157:H7 can be detected using what type of agar?

Answer 2

Chromogenic agar

Question 3

What Gram negative bacilli has a carrier state where people are infected but not sick? In which part of the body does the bacteria stay and continuously produce toxins?

Answer 3

Salmonella Typhi

Gallbladder

Question 4

What condition of the intestine is essential for the growth of Salmonella?

Answer 4

Intestinal inflammation

Question 5

What gram negative bacilli has an ID50 of 10?

Answer 5

Shigella has an infectious dose of 10 microorganisms

Question 6

What gram negative bacilli causes rice water stools and what is the disease called?

Answer 6

Vibrio cholerae- Cholera

Question 7

What two gram negative bacilli are medically important for individuals with Cystic Fibrosis?

Answer 7

Pseudomonas aeroginosa

Burkholderia spp.

Question 8

Pneumonia that is likely to be untreatable with antibiotics might be caused by a gram negative bacilli called?

Answer 8

Legionella

Question 9

Would E. coli infections be treated with penicillin? Why or why not?

Answer 9

No - they are a gram negative bacteria and since penicillins target the peptidoglycan production in gram POSITIVE bacteria, this antibiotic would not be very effective.

Question 10

Why is urethritis (infection of the urethra) frequently preliminary to further infections of the urinary tract?

Answer 10

Bacteria can ascend the urinary tract and cause infections further up, for example the bladder, ureters and kidneys

Question 11

Why is E. coli the most common cause of cystitis, especially in females?

Answer 11

The female anatomy means the urethra is closer to the anus where E. coli is commensal, than males.

Question 12

What are 4 examples of pathogenic strains of E. coli discovered during this unit?

Answer 12

ETEC - Enterotoxigenic E. coli.
EIEC - Enteroinvasive E. coli.
EPEC - Enteropathogenic E. coli.
EHEC - Enterohemorrhagic E. coli (aka 0157:H7)

Question 13

If you adequately cook food contaminated with ETEC, would you be able to safely eat it?

Answer 13

No - the toxin that ETEC produces is heat stable.

Question 14

During an infection of EIEC, where do these bacteria multiply?

Answer 14

Inside the intestinal epithelial cells.

Question 15

What does EPEC do to the intestinal epithelial cells?

Answer 15

Destroys the brush border microvilli.

Question 16

What is 0157:H7 and what toxin does it produce?

Answer 16

EHEC - Enterohemorrhagic E. coli - releases shiga-like toxin (as in Shigella)

Question 17

Which food is most likely associated with Salmonella spp?

Answer 17

Chicken / eggs

Question 18

What toxins are produced by Salmonella that induce illness?

Answer 18

• Enterotoxin - affects the enteric system

- Cytotoxin - affects cells

Question 19

In which organ of the body does Salmonella Typhi exist in carriers?

Answer 19

The gallbladder

Question 20

What does Salmonella do to the M cells of the intestinal tract?

Answer 20

Causes membrane ruffle, enters the cell and multiplies inside. Occasionally can go on to enter lymphatic system and bloodstream.

Question 21

What does Salmonella do to cause an inflamed gut and why?

Answer 21

Uses a Type III secretion system

Question 22

What disease does Shigella cause and what causes this?

Answer 22

Dysentery - through Shiga exotoxins.

Question 23

How does Shigella avoid immune defences after multiplying inside the M cell of intestinal tract?

Answer 23

Invades neighbouring cells.

Question 24

What does Shigella infection do to the intestinal epithelial cells?

Answer 24

Abscess forms

Question 25

What colour are Salmonella colonies on XLD agar?

What colour are Shigella colonies on XLD agar?

Answer 25

Salmonella - black colonies

Shigella - clear red colonies

Question 26

What are the symptoms of cholera infection and what happens because of this symptoms?

Answer 26

Massive fluid loss
Rice water stools
Leads to hypovolemia and can cause shock and death.

Question 27

What disease can Proteus mirabilis cause?

Answer 27

Urinary Tract Infections

Question 28

What does Klebsiella spp look like on MAC and why?

Answer 28

Goopy slimy pink colonies. Pink because they ferment lactose and slimy because they are motile - they swarm the plate.

Question 29

What would the benefit be of bacteria having exotoxins?

Answer 29

To kill off competing bacteria - make a niche.

Question 30

In an AB exotoxin, which part binds and which part is responsible for the toxic effect?

Answer 30

A - toxogenic

B - binding subunit.

Question 31

What is LPS?

Answer 31

Lipopolysaccharide - an endotoxin in Gram negative cell walls. Lipid

Question 32

What temperature does Campylobacter jejuni best grow at?

Answer 32

43 deg celcius

Question 33

What enzyme does Helicobacter pylori produce to be able to live in the stomach acid?

Answer 33

Urease - hydrolyses ammonia and provides a local alkaline environment to survive in an acidic environment. A urease breath test can indicate a possible H. pylori infection.