Bacteriology - Part IV (Virulence & Opportunistic)

Question 1

What are the bacterial virulence factors?

Answer 1

• Secretion systems and secreted effectors that can modulate host processes
• surface molecules
• toxins

Question 2

What are secretion systems used for?

Answer 2

• delivery of bacterial proteins across membrane

- some systems are dedicated to delivery of bacterial “effector” proteins or virulence factors

Question 3

What are the different secretion systems we need to know?

Answer 3

• T4S
• T3S
• Sec

Question 4

T3S and T4S qualities

Answer 4

• Go across PM, OM, and host membrane
• Translocate proteins (effectors) across host membranes
• Different structural forms

Question 5

T3S and T4S are only found in what type of bacteria?

Answer 5

Gram -

Question 6

Sec qualities

Answer 6

• Sec gets proteins to the periplasmic space

- exports cell wall anchored proteins as well as others that aren’t anchored

Question 7

T3SS

Answer 7

• Evolved from flagella
• Found in gram -
• Shigella, Salmonella, Y. pestis, E. coli

Question 8

T4SS

Answer 8

• Evolved from conjugation systems, pili comparison
• Found in gram - or gram +
• Pertussis, helicobacter pylori, Legionell

Question 9

Sortase-Mediated Secretion and Anchoring

Answer 9

• Cell wall anchored (CWA) proteins are covalently linked to cell wall via the Sortase transpeptidase
• Substrates have N- terminal Sec signal sequence and C-terminal cleavage motif
• Sorting signal recognized, Sortase cleaves and covalently links protein to cell wall

Question 10

Functions of CWA

Answer 10

• critical for virulence of Gram + pathogens
• Ex: S. areus – can express up to 24 different proteins
• Iron binding proteins – extracts Fe from Hb
• Adhesion promotion factors – anchor proteins
• Superantigens
• Receptor triggers

Question 11

Exotoxin

Answer 11

• protein secreted by bacteria
• specific function and target
• denatured by boiling
• e.g. diptheria, pore forming cytotoxins

Question 12

Endotoxin

Answer 12

• Component of cell wall or membrane
• systemic
• not denatured by boiling
• e.g. LPS in gram - or LTA in gram +

Question 13

Exotoxin Classifications (types)

Answer 13

• Type I
• Type II
• Type III

Question 14

Type I Exotoxin

Answer 14

-Target cell surface but are not translocated
E.g. Superantigen – indiscriminate interaction of peptide and receptor
Ex: TSST (toxic shock syndrome toxin)
-Massive pro-inflammatory cytokine release = systemic shock
-Produced by few S. areus strains
Triggered via tampons due to the increase of O2 concentration&raquo_space;> simulates TSST-1 production of S. areus in the vagina

Question 15

Type II Exotoxin

Answer 15

-Act on cell membranes, such as phospholipases and pore-forming cytotoxins
Ex: Strep hemolysis – exotoxins form pores in the cell membranes which cause lysis of blood cells

Question 16

Type III Exotoxin

Answer 16

-A-B toxins with two functional components
*B binds to surface receptor and allows endocytosis of A-B into the cell
*A is enzymatically active and upon dissociation from B becomes active within the cell
Ex: Diptheria Toxin (DT is acquired by phage)
Prevents protein synthesis within the cell
Extremely small lethal dose (only .1 ug per kg)

Question 17

C. Diff characterization

Answer 17

-Gram positive bacillus – spore forming
Spore makes transmission a large concern
14k deaths a year linked
-Range of disease from diarrhea to pseudomembranous colitis
-Toxigenic strains produce 2 AB (Type III) toxins – responsible for psudo colitis

Question 18

C. Diff Infection

Answer 18

• Colonizes the intestine after disruption of the normal intestinal flora
• High use of antibiotics can tank the flora in the gut and thus increase the risk of C.diff colonization

Question 19

4 things a successful pathogen must accomplish

Answer 19

1. Enter the host
2. Find an appropriate niche in the host
3. Grow and replicate in the host
4. Overcome host defenses