L16- Pathogenicity of bacteria

Question 1

Which pathogen are plants covered with, which means you shouldn’t take flowers into hospitals?

Answer 1

Pseudomonas aeroginosa. A gram negative opportunistic pathogen. Infects burns- causes cystic fibrosis.

Question 2

Which pathogen colonises intravenous catheters?

Answer 2

Staphylcoccus epidermidis

Question 3

Why are these catheter infections hard to treat?

Answer 3

The S. epidermidis grow on the catheter, then the blood plasma proteins form a coat around it. There’s now a biofilm, as the bacteria produce more extracellular polymers which protect them.

Question 4

How do highly virulent pathogens like Mycobacterium tuberculosis last so long?

Answer 4

TB can cause disease after long incubation period
Bacteria grow in the macrophages in the lungs
Very resistant to dessication.

Question 5

What’s a Ghon complex?

Answer 5

A necrotic area containing bacteria and dead/dying macrophages.
Granulomas make up Ghon, macrophages block it in,

Question 6

What disease does Treponema pallidum cause? What are the stages of this infection?

Answer 6

1. Flexible helical bacteria- primary lesion at site of entry in 2 weeks.
2. Secondary stage- (after 10 weeks) symptoms can disappear or cells spread to eyes, joints, skin rash.
3. Latent phase- 40% develop tertiary syphilis-> insanity and death. Or just goes away.

Question 7

What are Koch’s postulates?

Answer 7

Proving cause and effect in microbial infections

1. Organism found (was done with anthrax)
2. Grow organism outside body in the lab
3. Organism must reproduce disease when put in animal
4. Re-isolate organism from test animal

Question 8

What are some problems with Koch’s postulates?

Answer 8

1. Sometimes cannot grow cultures in lab media
2. Ethical problems e.g. Aids, ebola
3. No suitable animal models. (ended with unethical experiments on humans who didn’t understand)

Question 9

What is virulence?

Answer 9

The degree of pathogenicity. Minimum number of bacteria needed to cause disease.

Question 10

How is virulence measured?

Answer 10

By LD50 (lethal dose)
Dose needed to kill 50% of animals/cells in a given time

Question 11

Comparing 2 Ld50s, which strain is more pathogenic?

Answer 11

The one with the lowest LD50=more pathogenic higher virulence

Question 12

What are the virulence determinants produced by the bacteria?

Answer 12

1. Capsule of poly-D-glutamic acid which prevent it being engulfed by phagocytosis.
2. Toxins- released into the bloodstream, killing the host.

Question 13

How do pathogens adhere to the epithelia?

Answer 13

1. Fimbriae- e.g. E coli. Have a tip adhesin (protein H) which attaches specifically to mannose receptors in the colon.
2. Non-fimbrial adhesins- protein can cover the bacterial surface and mediate attachment to an epithelial cell.
   e. g. streptococcus pyogenes- sore throat and impetigo.

Question 14

What’s the skill of Listeria monocytogenes?

Answer 14

It can invade intestinal mucosa and spread intracellularly between cells without emerging from the cell. It induces phagocytosis and then escapes the phagosome and moves by polymerising actin.