Bacterial Pathogenesis Lecture 9-11

Question 1

What is a selective medium?

Answer 1

Selects for growth of a desired organism, stopping the growth of or altogether killing non-desired organisms

Question 2

What is a differential medium?

Answer 2

Contains compounds that allow groups of microorganisms to be visually distinguish between groups of bacteria (becuase they look different)

Question 3

In order to isolate bacteria that is not responding to antibiotics (penicillin and erythromycin) but is susceptible to ciprofloxacin- what growth conditions should you use?

Answer 3

Erythromycin and penicillin

Question 4

How can you prevent a cholera outbreak?

Answer 4

• Vaccine (toxoid vaccine or a live attenuated vaccine) for localized immunity
• travel safe: clean drinking water, food and hygiene

Question 5

What are the virulence factors for V.Cholerae?

Answer 5

Cholera Toxin (CT), and toxin-coregulated pili (TCP)

Question 6

What is TCP?

Answer 6

Adhesion needed to colonize the small intestine

Question 7

What is CT?

Answer 7

• enterotoxin
• B subunit binds to a structure on the host cell
• A subunit: delivers toxic enzyme

Question 8

How does CT enter the host cell?

Answer 8

• Endocytosis, then the vesicle transports to golgi, then ER
• A subunit activates G protein, which activates adenylate Cyclase
• cAMP opens the ATP-gated anion channel

Question 9

How does the CT-A subunit interrupt the normal GPCR-G pathway?

Answer 9

• adds ADP to the G alpha subunit so it cannot associate with GCPR
• this causes ADP to bind to AC and leads to Cl- secretion (cAMP, then PKA)

Question 10

How does CT lead to electrolyte imbalance? How does water get drawn into the lumen of the intestine?

Answer 10

• Cl is secreted from the cell into the lumen of the intestine, so Na+ cannot be absorbed by the cell
• there is a higher concentration of Na+ and Cl- in the intestine, and this draws water out due to osmotic imbalance

Question 11

How can you get immunity to ETEC?

Answer 11

Dukarol vaccine: provides immunity to the heat-labile toxin of ETEC

Question 12

Why does the ETEC vaccine have inactivated forms of cholera and not E. Coli?

Answer 12

The heat labeled toxin (LT), has the same 3D structure, receptor and mechanism of action as cholera, so antibodies for cholera bind to ETEC LT toxin and neutralize it

Question 13

Why are secretion systems essential?

Answer 13

• provides movement across the bacterial cell envelope
• attaches to surfaces and transfers DNA
• does specialized functions in pathogens

Question 14

How are secretion systems classified?

Answer 14

• transported effector molecules
• targets
• producing cell type

Question 15

Which types of bacteria contain Sec, Tat and T4SS?

Answer 15

Both gram neg and positive

Question 16

Which secretion systems have been identified in gram neg bacteria?

Answer 16

T1SS, T2SS, T3SS, T5SS, T6SS

Question 17

What is the type of secretion system that is found in both cell types?

Answer 17

T4SS

Question 18

What is the difference between a facultative and obligate intracellular pathogen?

Answer 18

Facultative: can live outside or inside the pathogen
Obligate: must live within host cells

Question 19

What are the advantages to being an intracellular pathogen?

Answer 19

• access to nutrients
• osmotically balanced environment
• protection from immune system
• protection from antibiotics that don’t go through the cell membrane

Question 20

What virulence factors do intracellular bacteria need?

Answer 20

• something that allows entry into the cell

- something that allows their survival once inside

Question 21

What is an invasin?

Answer 21

A protein that allows entry into the host cell

Question 22

Why are injectisomes advantageous?

Answer 22

• protein effector is not diluted into the environment

- the protein effector can act on internal host cell structures

Question 23

What is a pathogenicity island?

Answer 23

• Genetic elements that are acquired by horizontal gene transfer
• encode virulence factors and are normally absent from non-pathogenic strains

Question 24

What is the structure of a T3SS?

Answer 24

• translocation pore, needle, basal body

Question 25

What are the two types of salmonella?

Answer 25

S. Typhi (blood), and S. typhimurium (GI tract)

Question 26

How do you treat the two types of salmonella?

Answer 26

Typhi: antibiotics
Typhimurium: rehydration therapy

Question 27

What is involved in the pathogenesis of salmonella infections?

Answer 27

Two SPIs:
SPI-1-encodes a T3SS that is needed for cell invasion
SPI-2: needed for intracellular survival inside the host cells

Question 28

What does SPI-1 do?

Answer 28

Injectisome for internalization of bacterium: injects invasin proteins into intestinal epithelial cells, which triggers actin rearrangements inside the host cell— causes membrane ruffling and formation of pseudopods that engulf the bacterium and internalize it inside the vacuole

Question 29

What is SPI-2?

Answer 29

• Injectisome for replication inside vacuole; injects effector proteins into cytoplasm/endomembrane system
• effector proteins modify the vacuole membrane and maintain it so the bacteria can reproduce (otherwise would be killed)
• it also stops lysosome/phagosome fusion and killing