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L11/12 Microorganisms in disease - infection


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pathogenicity
capacity of a micro-organism to cause an infection; requires transmissibility, establishment in or on host, harmful effects & persistence
virulence
relative degree to which a micro-organism is able to cause disease (may be used interchangeably to describe pathogenicity)
infectivity
the ability of micro-organism to become established on/in; requires microbial ligand and host cell surface receptor
P fimbriae
E. coli ligand that binds to glycolipids on human uroepithelial cells
protein-F
S. pyogenes ligand that bind to fibronectin (large multifunctional glycoprotein found in connective tissue, on cell surfaces and in various body fluids)
haemagglutinin
Influenza ligand that binds to respiratory epithelial silica acid receptors
virulence factors
components of micro-organisms that result in harmful effects; e.g. facilitate adhesion, toxic effects, tissue-damage, interference with host defence mechanisms, facilitation of invasion, modulation of host cytokine responses
chain of infection
pathogenic organism, reservoir, exit, transmission, entry, susceptible host
incubation period
period between infection with the organism and manifestation of clinical features ;e.g. chickenpox: 10-21 days
period of infectivity
period during which a transmissible organism may be transmitted to another person; e.g. chickenpox: from 48hrs before the onset of the reach to when all lesions have crusted over
inflammation
response to invasion/tissue damage; activation of complement and clotting systems, fibrinolysis and kinin system; leucocyte adhesion and production of inflammatory mediators; phagocytosis of foreign material
Streptococcus pyogenes
syndromes associated with _________ _______: erysipelas, strep throat, scarlet fever, necrotising fasciitis
hyaluronidase & streptokinase
S. pyogenes virulence factor: break down connective tissue components – facilitate tissue invasion
toxic shock syndrome toxin
S. pyogenes virulence factor: causes a syndrome very similar to that caused by endotoxin release
erythrogenic toxin
S. pyogenes virulence factor: causes the rash of scarlet fever (phage-encoded)
C5a peptidase
S. pyogenes virulence factor: inactivates complement and component C5a
Streptolysins -O & -H
S. pyogenes virulence factors: lyse red and white blood cells and platelets
abscess
an enclosed collection of pus - consequence of inflammatory response with phagocytosis of organisms
pyogenic
organisms that produce abscesses.
superficial
________ abscesses normally caused by Staph. aureus or Strep. pyogenes
deep
____ abscesses can be caused by any organism
endotoxin
component of Gram-negative bacterial cell outer membranes; released by dead/damaged cells; binds to host cell receptors, inducing physiologically damaging host responses; e.g. E.Coli & Neisseria meningitidis
lipopolysaccharide
active component of endotoxin; comprises a Lipid A, Oligosaccharide core & Polysaccharide 'O' antigen; e.g. E. coli O157
sepsis
severe host response to endotoxin
T-lymphocyte
host response to endotoxin: cytokine release (TNF-α, γ-interferon, interleukin-1); Fever, rigors, hypotension, tachycardia, collapse; Cardiac and/or renal failure
clotting cascade
host response to endotoxin: activation of _______ ________, leading to depletion of clotting factors and disseminated intravascular coagulation (DIC)
complement
host response to endotoxin: activation of _________
Botulism
caused by Clostridium botulinum (obligate anaerobe); ingestion of pre-formed toxin (contaminated food); infection of dirty wounds (trivial wounds); gastrointestinal colonisation (infants); diplopia, dysphasia, dysarthria, dry mouth, death (respiratory failure)
Tetanus
caused by Clostridium tetani (obligate anaerobe); infection of dirty wounds (may be trivial); toxin production (tetanospasmin); death caused by respiratory paralysis
tetanospasmin
produced on germination of spores; binds to nerve synapses; inhibits release of inhibitory neurotransmitters (e.g. gamma-amino butyric acid - GABA) in CNS
opisthotonos
arching of the back in tetanus
Mycobacterium tuberculosis
intracellular pathogen; granuloma production accounts for the main clinical and radiological features
Primary TB
Ranke/Ghon complex: solitary granuloma (nodule) with hilar granulomatous lymphadenopathy
Post-primary TB
Widespread granulomatous inflammation +/- cavitation, often apical
Miliary TB
Multiple disseminated 1-3mm pulmonary granulomas
Extrapulmonary TB
Diverse manifestations in bone, liver, kidneys, CNS etc.