The pathogenesis of bacterial infections Flashcards
1
Q
What is pathogenesis?
A
- all the cellular events leading to the development of disease
- bacterial pathogenesis - includes bacterial and host factor and interactions
2
Q
Are all bacteria pathogenic?
A
- no
3
Q
What is disease development dependent on?
A
4
Q
What is a pathogen?
A
- an organism with the ability to cause disease (damage the host)
5
Q
Who are important people who lead to discovery of bacteria etc?
A
- antoine van leeuwenhoek
- Pasteur and Henle - Germ Theory of Infectious Disease
- Koch - 1884/1890
6
Q
What are Koch’s postulates?
A
- the organism must be reguarly associated with the disease and its characteristic lesions
- the organism must be isolated from the diseased host and grown in culture
- the organism must reproduce when a pure culture of the organism is introduced to a healthy, susceptible host
- the organism must be re-isolated from the experimentally infected host
7
Q
What causes peptic ulcer disease?
A
- H.pylori (85-95%)
- depends on strain and host characteristics + conditions
8
Q
What are the weaknesses of Koch’s postulates?
A
- some agents cant be grown in culture
- some agents are present is sick and healthy hosts (opportunistic infections by commensals)
- no animal model for experimental infection
- no characteristic lesions
- multi-factorial diseases
- epidemiology - possible to establish role of pathogen as cause of disease, even if the 3 postulates cannot be proven
9
Q
Why are infections not in all hosts?
A
- infection depends on host factors / genetics
- some organisms have different genomes that affect different hosts
- need to have exposure to have chance of transmission
10
Q
What is pathogenicity?
A
- ability to cause disease
11
Q
What is virulence?
A
- degree of pathology caused by organism
12
Q
What is infectivity?
A
- the capacity of the organism for transmission/ spreading to new hosts
13
Q
What affects the infectivity?
A
- type of pathogen
- mode of infection
- strain, species
- survival
- dosage
- stage of growth
- e.g. log phase - not as infective as focused on growing
- host factors
- age, gender, immune status etc.
- environmental factors
- temp, humidity, vector
- virulence
- species, strain
14
Q
What affects transmissibility?
A
- capacity to grow in parts of the body
- acute - short and fast
- chronic - long and slow
- capacity to readily exit infected host
- orifices
- vectors
- capacity to survive in transit between hosts
- enviro
- sporulation
15
Q
What are exogenous and endogenous pathogens?
A
- exogenous - from outside, true pathogens, associated with disease only
- endogenous - commensal/ opportunistic - if get into wrong body compartment - persistent infections
16
Q
Whats the 5 step programme to becoming a successful bacterial pathogen?
A
- attach and enter the host body
- evade the host defence mechanisms (innate and adaptive)
- mutiply and spread - nutrients
- damage to host - direct and indirect through immune response
- transmission from one host to another healthy host
17
Q
How do bacterium reach a host?
A
- motility and taxis (directed motility)
- flagella - polymer of flagellin protein
- move towards nutrients and away from bile/ acid
- long - up to 20um - helical
- highly immunogenic - evolutionary conserved
18
Q
How do bacterial enter the host?
A
- skin/ extended mucosa - direct contact
- body orifices
- repro tract
- inhalation
- ingestion
- eyes/ ears
- injected into blood stream - arthropod borne
- environment, sporulation, reservoire host
19
Q
What are the body’s defences against pathogens?
A
- mucin/ mucus
- microflora - compete for nutrients
- stomach - weak - 10^1 - 10^3
- colon - strong - 10^10 - 10^11
20
Q
What are the bacterias strategies to invade?
A
- molecular mimicry
- switch off irritants
- hide inside ep/ immune cells
- prevention of activity of imm response e.g. release toxins
21
Q
What can the bacterium then choose to be?
A
- once theyve passed the dermal and mucin layers, and overcome the immune responses etc.
- have to choose whether to be IC or EC
22
Q
How do bacteria damage the host?
A
- lysis of host cells
- disruption of microflora
- disruption of immune system
- disruption of barrier function
- toxins:
- endotoxins - non-proteinaceous - LPS/ lOS - fever markers
- exotoxins - proteinaceous - proteolysis, neurological
23
Q
How does transmission occur?
A
- immune system responds to toxins
- Pus produced - DNA, dead immune cells
- spreading factors - proteins like DNases and proteases - facilitate spread into neighbouring tissues
- TB - coughing
- Anthrax - inhalation of spores
- E.coli - contaminated water
- vectors
24
Q
A
25
4 main issues for bacterial survival outside?
* nutrient availability
* lack of adherence sites and niches similar to hosts
* exposure to noxious chemicals/ predators
* exposure to sunlight and extreme weather
26
What are the colonisation factors?
* adhesins - pilli
* bacterial motillity and chemotaxis - flagella
* enzymes that break down mucins and host tissues
* metabolism - use of specific nutrients
27
What does invasiveness depend on?
* presence of capsules e.g. Bacullus anthracis, Pastreulla multocida, streptococcus pneumoniae)
28
How are some bacteria resistant to phagocytosis?
* inhibit opsonisation
* kill the phagocytes
* live in the acidic enviro
* stop the lysosomes fusing with phagocytic vacuole
* use them as transport
* escape quickly
29
What are exotoxins?
* produced mainly by G+ve bacteria/ some -ve e.g. E.coli
* proteins - few enzymes
* readily separated from bacteria by filtration
* fatal in small doses
* thermolabile
* cytopathic effects:
* verotoxins - E.coli
* haemolytic - staphylococci toxin
* necrotis - tetanolysins
* immunogenic
30
What is the role of Aggressins?
* contribute to the abiltiy of capsulate and non-capsulate bacteria to invade and multiply in hosts tissues
* enhance permeability of tissues - increase spread
* hyaluronidase
* coagulase
* fibrinolysin/ kinase
* depolymerising enzymes (lipases. proteases, nucleases)
* deoxyribonuclease
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