MELS223 Lecture 14 8/21/2013 4:00:00 PM
Toxin= microbial factor that damages the host
Shia or Shiga-like toxins kill host cells by blocking protein synthesis
Adhesion cell doesn’t damage deliberately.
High local concentration of toxin is needed to damage cells.
3 different types of toxins
1. surface acting toxins. Acts on surface of human cell. Binds to receptor
on plasma membrane and causes damage to human cell.
2. Pore-forming toxins. Puts holes in phagosome to help bacteria escape
(Listerilysin). Others also put holes in membrane – plasma membrane.
3. A/B toxins – have 2 components, A domain and B domain. Linked
together in same protein and separated later on or actually separate
toxins. A subunit has toxic activity. B subunit function is to bind to surface
and help deliver A into cell.
Diptheria toxin- exits from endosome and affects protein synthesis.
Surface acting toxins
Made by Staphlylococcus aureus.
Gram positive cocci, colonize skin and anterior nares.
Disease: Skin infections, Medical implant associated infections, invasive
disease (endocarditis), Necrotizing fasciitis – in blood stream.
*Toxic Shock Syndrome TSS
20% of genes vary in different strains of same species of Staph aureus.
Different virulence factors.
Toxic Shock Syndrome
Tampon became colonized by S.aureus
TSST is a superantigen that stimulates T cells, causing
uncontrolled cytokine (IL2) release, leading to septic shock 0
decreased tissue perfusion and oxygen delivery.
APC and TCR bind – T cell is stimulated to make cytokines and
this is very specific – 1 in 10,000 When superantigen around – binds to both APC class II MHC and
TCR, antigen does not have to be present and stimulates then
without CD4 needed either! Cytokines produced a lot!
Pore Forming Toxins
Large pore-forming toxins (20-30nm pores)
Extra cellular pathogens (L.monocyhtogenes – Listeriolysin O, C.
perfringens – Perfringolysin O, S.pyogenes, S. pneumonia
Their receptor is cholesterol
Small pore-forming txin: alpha-toxin (S.aureus)
Water rushes into cell as hypotonic environment, pressure inside
cell builds and pops!
Characteristics of alpha-toxin
Strains that make most alpha toxin are most virulent
Might be possible to use alpha toxin to make vaccines. Made it so
that it can no longer make pores. Used to immunize mice, mouse
generates antibodies against it.
Mice survived when injected w