M3- Koch's postulates - basis of infectious disease I Flashcards
what is Koch’s postulates germ theory of disease?
- the microorganism is present in every case of the disease but absent from healthy organisms
- the suspected organism must be isolated and grown in a pure culture
- the same disease must result when the isolated microorganism is inoculated into a healthy host
- the same microorganism must be isolated again from the diseased host
Name some infectious agents.
- bacteria- prokaryotic, single celled organisms
- viruses- non-living, obligate parasites
- fungi- eukaryotic single to multi-cellular infectious agents
- protozoa- amoeba
- parasites
- prions -infectious proteins
what is the microbiome?
community of cells that are not part of our body directly
what is AMR?
antimicrobial resistance
what are endogenous micro-organisms?
microorganisms within the body
what are exogenous microorganism?
comes from outside the body ( not normal flora)
What is free living organism?
- found in soil
- feed on dead organic material
what is commensal organism?
organism gains advantage but host does not gain from association
What is mutualistic organism?
(symbiotic) relationship , when host and organism gain mutal value
what is parasitic organism?
live on or in living creatures causing harm/damage to the host
what is the relationship between bacteria in a mutualism state to parasitic state?
dynamic relationship (bacteria can shift to becoming parasites)
Describe the mutualistic relationship.
- organism can produce nutrients or vitamins
- can degrade harmful chemicals
- can exclude access/colonisation by exogenous pathogens (colonisation resistance)
what limits microorganisms colonising?
shedding of surface epithelium
what makes up the oral microbial flora?
- mucosa of lips, cheeks and palate
- tongue
- tooth surfaces
- saliva
- tonsillar area
what oral microbial flora is the only naturally non-shedding community in the body?
teeth
what makes oral microbial sampling difficult?
- stimulated /non-stimulated salvia
- mucosal surfaces -difficult to swab
- plaque
what controls many commensals?
antibodies
what can precipitate disease?
- change in state
- (broad spectrum antibiotics disturb microflora)
what is the definition of pathogen?
- a harmful organism that produces a pathology
- virulence and its factors
what is the definition of commensal?
- an organism that is part of the normal flora
- often mutualistic relationship
- endogenous
what is the definition of opportunistic pathogen?
-an organism that causes infection when opportunity / change in natural immunity arises e.g. in an immunocompromised individual
what is the definition of contaminant?
an organism that is growing in a culture by accident
what is virulence?
the capacity of a microbe to cause damage to the host
Name the virulence factors.
- Adhesin
- Invasin
- Impedin
- Aggressin
- Modulin
what effect does adhesion have?
enables binding of the organism to host tissue
what effect does invasin have?
enables the organism to invade a host cell/tissue
what effect does impedin have?
enables the organism to avoid host defence mechanisms
what effect does aggressin have?
causes damage to host directly
what effect does moulin have?
induces damage to the host indirectly
What is molecular koch’s postulates?
-A virulence trait should be strongly associated with pathogenic strains of the species
• Inactivation of gene(s) associated with the virulence trait should decrease pathogenicity
• Restoration of an inactivated/mutated gene with the wild type restores pathogenicity
• The gene is expressed at some point during infection.
• Antibodies directed against the gene product protect the host
what are the limitations?
- organism cannot be cultured/isolated -obligate intracellular organisms
- organism is a human pathogen- no model organisms to inoculate
what is the definition of obligate pathogens?
must cause disease for transmission
what is the definition of the opportunistic pathogens?
Do not have to cause disease for transmission
what is the definition of “accidental” pathogens?
disease hinders or prevents transmission (host death)
what is the only method of transmission of an obligate pathogens?
human disease
what is epidemiology?
the study of the occurrence , spread and control of disease
what is considered for any organism?
- infective dose
- virulence of the organism
- host status (resistance)
what is sporadic occurrence?
comes and goes in low numbers -occassionally it occurs
what is endemic occurrence?
present all the time in population but in low levels i.e common cold
what is epidemic occurrence?
sudden increase in disease in a location of a period time
what is pandemic occurrence?
same as epidemic but geographical concept - 2 or more contenants
what is prevalence?
proportion of population affected
what is retrospective?
clinical effect studied
what is prospective?
population exposed to presumed cause studied
what is microbiota/flora?
endogenous population of microbes
what is Koch’s postulates?
basis for demonstrating cause of disease
what is pathogenicity?
capacity to cause disease/damage
what is resistance?
ability to resist anti-infective measures
