MIIM20002 Lecture Notes - Lecture 2: Collagen, Glycocalyx, Antibody
29 Jun 2018
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Pathogens: micro-organisms that cause disease (when isolated from an infected individual, are
most likely to be the cause of disease) ā āhave an inherent ability to cause diseaseā
ā¢
Opportunistic pathogens: cause disease when defence mechanisms have been compromised
ā¢
Normal microbiota (commensals, normal flora): that diverse group of microbes associated
with the body from shortly after birth until death - found on skin and mucous membranes
ā¢
Virulent organism: one that is most likely to be the cause of disease, i.e. a pathogen (virulence
is a measure of a microbeās ability to harm the host)!
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Avirulent organism: one that will not cause disease in a host with a normal immune system
ā¢
Virulence determinants: characteristics that make an organism virulent (e.g. pili, fimbriae,
siderophores (allows uptake of Fe), capsules, toxins, enzymes) (can arise from gene
acquisitions from other bacteria, often via bacteriophages or through conjugation)
ā¢
Pathogenesis of infectious disease: definitions
colonise surfaces/niches (microenvironments), but donāt cause disease there, i.e. lacking some
virulence determinants at least
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have a specific and sustainable association with their host (not all organisms can be
commensals)
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can be pathogenic if moved (i.e. association is āsite specificā)
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contribute to an efficient immune system (non-specifically stimulate the immune system) and
host metabolism
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protect host against disease (prevent colonization; produce pathogen growth inhibitors: fatty
acids, bacteriocins etc.; deplete nutrients)
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can be transient (microbiota can disappear) or permanent (however we have a shared ācoreā
microbiota)
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Normal microbiota (commensals, normal flora)
Colonisation: both commensals and pathogens colonise
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Commensals live mutualistically with the host (role in human nutrition and metabolism)
ā
Pathogens cause disease in host
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The outcome of colonisation differs for commensals and pathogens
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Disease requires ability to damage host to evade some host immune defences
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Normal microbiota versus pathogens
Colonisation via adhesion
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Penetration through epithelia or into epithelial cells
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Replication requires evasion of the immune system
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Asymptomatic:
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Host tissue damage
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Disease
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Dissemination (spread to other tissues/hosts)
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Immunity death/chronic disease
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Symptomatic
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The process of infectious disease
Depends on interactions between ligands (binding molecules/adhesins) on the micro-organism
surface, and specific receptors on the epithelial cell surface
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Receptor-ligand interactions may involve many types of molecules: polysaccharides,
glycoproteins, teichoic acids, sialic acids, gangliosides, fibronectin etc.
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Colonisation of host tissue
2 Bacterial Pathogenesis
Tuesday, July 29, 2014
5:30 PM
Microbes Page 1
Document Summary
Pathogens: micro-organisms that cause disease (when isolated from an infected individual, are most likely to be the cause of disease) (cid:862)ha(cid:448)e a(cid:374) i(cid:374)here(cid:374)t a(cid:271)ilit(cid:455) to (cid:272)ause disease(cid:863) Opportunistic pathogens: cause disease when defence mechanisms have been compromised. Normal microbiota (commensals, normal flora): that diverse group of microbes associated with the body from shortly after birth until death - found on skin and mucous membranes. Virulent organism: one that is most likely to be the cause of disease, i. e. a pathogen (virulence is a (cid:373)easure of a (cid:373)i(cid:272)ro(cid:271)e"s a(cid:271)ilit(cid:455) to har(cid:373) the host(cid:895)! Avirulent organism: one that will not cause disease in a host with a normal immune system. Virulence determinants: characteristics that make an organism virulent (e. g. pili, fimbriae, siderophores (allows uptake of fe), capsules, toxins, enzymes) (can arise from gene acquisitions from other bacteria, often via bacteriophages or through conjugation) ; deplete nutrients) (cid:272)a(cid:374) (cid:271)e tra(cid:374)sie(cid:374)t (cid:894)(cid:373)i(cid:272)ro(cid:271)iota (cid:272)a(cid:374) disappear(cid:895) or per(cid:373)a(cid:374)e(cid:374)t (cid:894)ho(cid:449)e(cid:448)er (cid:449)e ha(cid:448)e a shared (cid:862)(cid:272)ore(cid:863) microbiota)
