Microbial infection Flashcards
What does the innate immune system consist of
notmal microbiota
physicals barriers
chemical barriers
phagocytic cells
How do normal microbiota contribute to the immune response
- offer competition when pathogens are looking for colonisation sites
- produce antibiotic substances which suppress growth of competing organisms (bacteriocins)
- may produce toxic metabolic products to inhibit other microorganisms
- may alter pH (lactobacilli)
Physical barriers
skin:
-secrets sebum and fatty acids to inhibit growth
mucomuciliary clearance
-particles settle on sticky mucus of respiratory epithelium
-debris transported by cilia to oropharynx where its swallowed
Flushing:
-urinary tract
peristalsis:
-GI
Chemical barriers
-Mucus
-Antimicrobial proteins
lysosome
lactoferrin (antioxidant)
defensins (defence peptides)
-gastric acid
-plasma proteins
complement
CRP
MBL
Transferrin
Phagocytic cells
Process by which the body destroys dead or foreign cells
Describe the infection process
An infection occurs when a microorganism causes ill health
2 ways:
-invading host tissues
-exerting effects from mucosal surfaces
commensal
microorganism which forms part of the normal host microbiota
pathogenicity
the capacity to cause disease
virulence
the measure of capacity to cause disease
obligate pathogen
almost always associated with disease e.g. HIV
Conditional pathogen
may cause disease if certain conditions are met e.g. bactericides fragilis, Straphylococcus aures
opportunistic pathogen
usually only infects immunocompromised host
phneumocystis jiroveci
What are the steps of infection
- recognition
- attachment and entry
- multiplication
- evasion of host defences
- shedding
- damage
What are the four methods of establishing infection
- specific attachment and penetration mechanisms of host body surface
- introduced via biting arthropods
- skin wounds or animal bites
- only able to infect when host defences are impaired
What is tissue tropism
affinity for a specific tissue (supports growth of a particular microbe) influencing factors: pH Temperature physical barriers transcription factors presence of cell receptors
common examples
Helicobacter pylori = gastric mucosa
chicken pox = nerve cells
rhino virus = upper respiratory tract
virulence factors
-toxin secretion (toxigenesis) bacteria and fungi
-antibiotic resistance
-pilus formation
-capsule
iron transport systems
-adhesion factors
-enzymes (proteases, DNAses, lipases)
what are bacterial endotoxins
low toxicity
part of cell wall of gram negative bacteria
lipopolysacchride
low specificity
what are bacterial exotoxins
highly toxic
secreted from bacterial cells
produced by both gram positive and negative bacteria
can be converted into toxoids for vaccine use
tetanus toxin, cholera toxin etc.
Tell me about antibiotic resistance
genees on plasmids production of enzymes (β-lactamase) impermeability efflux mechanisms (move stuff out of cells) alteration of target site - HIV - MALARIA - TB - MRSA - VRSA
What three factors does transmission depend upon
- the number of microorganisms shed
- the number of microorganisms required to infection a fresh host (its efficiency)
- the microorganisms stability in the environment
Zoonoses vectors
invertebrate
-arthropods(malaria, yellow fever) and shellfish (Hep A, cholera)
vertebrate
-mammals (rabies, tapeworm) and birds (salmonella)
