Lecture 18: Trickery of Bacterial Pathogens Flashcards
1
Q
What are the human-microbe relationships?
A
- Colonization of human host
a. either as part of gut flora or harmony
with the host
b. or subverting host defences,
causing disease - Few microbes can invade tissues &
prod toxic substances/inflict damage
2
Q
Explain the production/delivery of various harmful factors?
A
- Organism needs to attach to hose tissue
- Need to replicate and evade immunity
- Damage host tissues to escape
3
Q
What is the process of disease?
A
- Microbes cause disease whilst stealing:
a. space
b. nutrients
c. and/or living tissue from host (e.g., us) - How do they do this?
a. Gain access to host (‘contamination’)
b. Adhere to host (‘adherence’)
c. Replicate on host (‘colonization’)
d. Invade tissues (‘invasion’)
e. Production of toxins, proteins, or other
agents that cause host harm (‘damage’)
4
Q
What are the 4 main mechanisms of bacterial pathogenicity? Give examples.
A
- Toxin ingestion following production
a. Bacillus cereus
b. not ingesting the pathogen, just its
toxin
c. sometimes associated with food
poisoning - Toxin production following
colonization
a. Clostridium botulinum - Invasion of host tissues without toxin
production
a. Mycobacterium tuberculosis - Tissue invasion followed by toxin
production
a. Vibrio cholerae
5
Q
How do we know if a pathogen causes a specific disease?
A
- Robert Koch
a. founder of public health
b. developed koch’s postulates - In 1800’s, discovered:
a. Tuberculosis = Mycobacterium
tuberculosis
b. Cholera = Vibrio cholerae
c. Anthrax = Bacillus anthracis
6
Q
What must bacteria do for successful infection?
A
- Sense environment
a. sense they’re inside the human host
e.g., sensing the temperature (37) - Need to know where they are…
- must express proteins to survive stress
- must express proteins required for
adhesion or invasion - May make toxins
- May enter host cell and replicate
- May spread through host cells
7
Q
what is the ‘course’ of an infectious disease?
A
- Incubation period: interval between
exposure and illness onset - Illness phase: may still be infectious
during incubation or convalescence
phases - Covalence phase: time of recuperation
and recovery from illness
8
Q
What are the principles of infectious disease/pathogenicity?
A
- Primary pathogen: microbe or virus that
causes disease in healthy individual.
a. E.g., plague, malaria, measles - Opportunistic pathogen: causes disease
only when body’s innate or adaptive
defences are compromised or when
introduced into unusual location
a. Can be members of normal microbiota
or common in environment
(Pseudomonas)
9
Q
What is meant by virulence?
What is meant by virulence factors?
A
- Refers to degree of pathogenicity
2. Allow microorganism to cause disease
10
Q
What are the common virulence factors?
A
- Endotoxin
- Capsule
- Antigenic phase variation
- Sequestration of growth factors
- Resistance to serum killing
- Antimicrobial resistance
11
Q
What are examples of virulence factors associated with specific pathogens?
A
- Exotoxin production
- Expression of adhesion factors
- Intracellular survival and manipulation
12
Q
What is molecular Koch postulates
A
show that a gene found in a pathogenic microorganism encodes a product that contributes to the disease caused by the pathogen - virulence factor
1. specific inactivation of gene(s) lead to
measurable loss in pathogenicity
2. reintroducing gene should restore
pathogenicity
3. gene causing virulence must be
expressed during infection
4. immunity must be protective
5. phenotype or property under
investigation should be associated with
pathogenic members of genus
13
Q
What are fimbriae?
A
- Key adherence factors
- How do cells avoid physical &
immunological removal?
a. adhere to cell surfaces and ECM
b. Solid surfaces (e.g., teeth, heart valves)
c. Other bacteria - How do cells adhere?
a. Often located at ends of fimbria or curli
b. & other outer membrane proteins - Adherence often combined with
manipulation of host cell signalling and
cytoskeleton (salmonella
a. Adherence
b. invasion
14
Q
How do microorganisms scavenge iron?
A
- free iron is low in bodily fluids (it is
bound to other things) - Many different systems for
scavenging:
a. Siderophores chelate available iron
& transport into bacteria
b. scavenged direct from iron-binding
proteins (e.g., lactoferrin-binding
proteins)
c. Often co-ordinately regulated
d. Some pathogens avoid problem by
cutting off need for iron (e.g.,
Treponema pallidum - syphilis) - Low level iron switches on aggressive
virulence factors
a. Diphtheria toxin (controlled by DtxR
repressor)
b. Shiga-like toxin
c. Pseudomonas aeruginosa exotoxin
A
15
Q
How do microorganisms avoid phagocytosis?
A
- Capsule around them - avoids
recognition by phagocyte
