M5-6 Flashcards
What are the 2 main routes of micro-organism transmission?
endogenous and exogenous
What does endogenous transmission mean?
- The infecting microorganisms are from from the body (own bacteria)
- Entry into abnormal site
- Reduced immunity
What does exogenous transmission mean?
- The infecting microorganisms are from elsewhere
- Transmitted through various mechanisms
What are the exogenous mechanisms through which microorganisms are transmitted?
- person-to-person
- food/water
- vectors
- fomites
- vertical
How are microorganisms transmitted from person-to-person?
- direct contact (touch)
- contaminated blood/fluids (sexual/needles)
- respiratory droplets/saliva
- airborne particles
How are microorganisms transmitted through food/water?
- ingestion
- poor sanitation - waterborne diseases
- food poisoning
Which organisms are common vectors?
usually arthropods (mosquitos, flies)
What are fomites? (and how are microorganisms transmitted via this route)
They are inanimate objects, organism survives on object and transmitted to next person
What is vertical transmission?
Transmitted from mother to child
Define commensal (normal flora)
Lives in/on human, causes no harm, may have benefits
What are colonisers?
Not normally on humans, but when it is it causes harm
What are pathogens?
May/may not normally live on human, causes harm
Describe the common commensal flora on the skin
- Dry areas: mainly gram negative
- Moist areas: gram negative and positive
Describe the common commensal flora in the GIT/UGT (urogenital)
- anaerobes most common
- enteric Gram negative bacilli
- Neisseria spp.
- Viridans streptococci
- Candida spp.
- some protozoa
Describe the common commensal flora in the URT (upper respiratory)
- streptococci
- staphylococci
- anaerobes
- yeasts
- spirochaetes
- Neisseria species
- haemophilus
Define pathogenicity
Ability of a pathogen species to cause disease
Define virulence
- Relative capacity to cause harm &often through toxins or invasion
- Reflects the degree of pathogenicity
- Greater virulence = severe disease and/or fewer organisms required to cause disease
What is a virulence factor?
The properties that allow an organism to cause disease and influence the severity of disease
Name the common virulence factors
- Adhesion (adhesins): Pili, Receptors
- Invasion (invasins)
- Toxins (aggressins): Endotoxin, Exotoxin
- Immune evasion (evasins): Capsules
Describe how bacteria are able to overcome the normal host immune mechanisms
Evading phagocytosis:
- capsules
- phagocyte toxins
- injects toxins into macrophage
- inhibits phagosome
- inhibits oxidative burst
