Bacteria pathogenesis Flashcards
Week 2
Pathogen
organisms capable of causing disease
Disease
clinical signs and symptoms of damage that occur in a host as a result of its interaction with an infectious agent
Overt/strict pathogens
only associated with human disease, not found as members of normal microbial flora.
Opportunistic pathogens
members of normal flora that only cause disease when in the right conditions/introduced into unprotected sites.
Facultative pathogens
can grow and survive in the environment as well as in the host. doesn’t have to cause disease to survive in environment (the ‘accidental host’)
what do virulence factors do?
facilitate the colonisation, growth and spread of bacteria in host
Areas of the body that should be microbe free
fluids: blood, CSF, urine
Tissues/organs: muscles, glands, brain etc
LD50
lethal dose 50: dose that gives 50% mortality in animal model
infective dose vs lethal dose
ID = dose at which you get infection LD = dose at which you die
Sub-clinical infection
Bacteria are present but no pathology
Name 6 examples of virulence factors in bacteria
- Adhesins: fimbriae, pili, outer membrane proteins
- Flagella for motility
- Help to obtain essential nuritents (e.g. siderophores)
- Toxins
- Capsule
- Type III secretory molecules
Give an ex of a bacteria which is an extracellular pathogen
Streptococcus pneumoniae
Ex of toxin producing bacterium
Clostridium botulinum
Clostridium tetani
Vibrio cholera
E.coli
Ex of an intracellular bacterium
Salmonella enterica serovar Typhimurium
Listeria monocytogenes
Virulence factors of S.pneumoniae
Capsule Surface adhesions Secretory IgA protease Neuroaminidase Pneumolysins (pore forming)
Endotoxin
On bacteria surface
Ex of endotoxin
LPS on Gr- bacteria
What receptor can detect LPS?
TLR4 (toll-like receptor 4)
What is LPS an example of?
PAMP
General symptoms of LPS
fever, diarrhoea, vomiting
Ex of bacteria that has LPS endotoxin
Salmonella
Exotoxin
Toxin released extracellular
Which is generally more toxin, endo or exo toxin?
Exotoxin
Which is generally more heat stable, endo or exo toxin?
Endotoxin
Enterotoxin
group of exotoxins that act on the small intestine
Ex of bacterium that release enterotoxins
C.dif
Cholera toxin
E.coli
Toxoid
inactivated toxin useful as a vaccine
Which bacteria has beta-haemolysin?
Streptococcus pyogenes
Botulinum toxin is an example of a…
Neurotoxin
Clostridium botulinum is a…
G+, spore forming anaerobe
Symptoms of botulinum toxin
flaccid paralysis (floppy baby) Respiratory arrest
What does botulinum toxin do?
Blocks release of Ach
Clinical use of botulinum toxin
Relief of spasticity Chronic migraine Excessive sweating Overactive bladder Botox
Is vibrio choleae Gr- or Gr+?
Gr-
What does cholera toxin do?
- conformational change of G protein
- adenyl cyclase constantly activated
- increase cAMP
- Cl- and Na+ into lumen, water follows
Cholera toxin results in
massive loss of fluid and electrolytes
4 strategies used by bacteria to evade immune system
- Hide: intracellular
- Antigenic variation and phase variation: change immunogeneicty to avoid established immune response
- Molecular mimicry
- Modify or block host response
3 ex of bacteria modifying/blocking host immune response
- capsule - phagocytosis
- IgA protease - antibody
- Type III secreted effectors - cell signally
Ex of pathogen which undergoes molecular mimicry
Haemophilus influenzae
Molecular mimicry may trigger…
Autoimmunity
Extra genome sequence, regions of DNA unique to a set or related pathogens usually transferred via horizontal gene transfer =
Pathogenicity islands
