Lect 11 & 12 - Micro-organisms in disease - Fri 16th Oct Flashcards
whats Pathogenicity
The capacity of a micro-organism to cause an infection
what is needed to increase Pathogenicity
Transmissibility
Establishment in or on a host
Harmful effect(s)
Persistence
what are the steps in the chain of infection?
entry susceptible host pathogenic organism reservoir exit transmission back to entry.
what is virulence?
May be used interchangably to describe pathogenicity
Virulence sometimes defined as the degree to which a micro-organism is able to cause disease.
what is Infectivity?
The ability of a micro-organism to become established on/in a host
what do pathogens use to increase infectivity?
Ligand-receptor interactions -
for example fimbriae used by E. coli to attach to glycolipids on human uroepithelial cells
give examples of Virulence mechanisms
Facilitation of adhesion
Toxic effect(s)
Tissue-damage
Interference with host defence mechanisms
Facilitation of invasion
Modulation of the host cytokine responses
Sometimes referred to as adhesins, aggressins, interferins, modulins etc.
what are virulence genes?
genes that encode for Virulence factors
what is an Endotoxin?
Released from damaged/dead cells
Active component is lipopolysaccharide - LPS
Binds to a number of host cell receptors
Induces a range of uncontrolled host responses
what type of bacteria have endotoxins as part of their cell wall?
Gram-negative
what happens in the host when endotoxins are released?
Systemic inflammatory response syndrome (SIRS)
what are the components of SIRS?
Uncontrolled T-lymphocyte response
Uncontrolled activation of the clotting cascade
Uncontrolled activation of complement
What does Uncontrolled T-lymphocyte response cause?
Cytokine release: TNF-α, γ-interferon, interleukin-1
Fever, rigors, hypotension, tachycardia, collapse
Cardiac and/or renal failure
what does Uncontrolled activation of the clotting cascade cause?
Disseminated intravascular coagulation (DIC):
Depletion of clotting factors
Bleeding tendency
give examples of gram negative bacteria which tend to give off endotoxins
E. coli and other Gram-negative bacilli
Neisseria meningitidis
describe symptoms of Neisseria meningitidis infection
Endotoxin-mediated increase in vascular permeability causes loss of protein, fluid and plasma into the tissues, with pathological compensatory vasoconstriction
what are exotoxins?
Proteins produced by living bacteria
Usually have quite specific effect(s) on host
what is Botulism caused by
Clostridium botulinum (obligate anaerobe)
Ingestion of pre-formed toxin (Contaminated food) Infection of dirty wounds (May be trivial wounds) Gastrointestinal colonisation
what does Botulinum toxin do?
prevents muscle contraction
whats is the clinical presentation of botulism?
Diplopia (double vision) Dysphagia (cant swallow) Dysarthria (cant talk) Dry mouth Death Respiratory failure
what causes Tetanus?
Clostridium tetani
Infection of dirty wounds
May be trivial wounds
what kills people with tetanus?
respiratory paralysis
how does the tetanus toxin interact with the body?
Binds to nerve synapses
Inhibits release of inhibitory neurotransmitters (e.g. gamma-amino butyric acid) in the central nervous system
what causes cholera?
Vibrio cholerae
what causes Diphtheria
Corynebacterium diphtheriae
what causes haemorrhagic colitis ?
E. coli O157 - an endotoxin
what causes Staphylococcal scalded skin syndrome
Staph. aureus
what casues Whooping cough (pertussis)
Bordetella pertussis
what causes Scarlet fever
Streptococcus pyogenes
what causes Scalded-skin syndrome
Staph. aureus epidermolysin
give a list of diseases caused by exotoxins
Botulism Tetanus Cholera Diphtheria Clostridium difficile haemorrhagic colitis Staphylococcal scalded skin syndrome Whooping cough (pertussis) Scarlet fever
what does Streptococcus pyogenes cause? (in addition to scarlet fever)
has virulence factors that promote connective tissue breakdown ands invasion
Streptococcal sore throat
Erysipelas
Necrotizing fasciitis
Scarlet fever
what virulence factors does Streptococcus pyogenes have?
Hyaluronidase and streptokinase C5a peptidase Streptolysins -O and –H Erythrogenic toxin (phage-encoded) Toxic shock syndrome toxin
what do Hyaluronidase and streptokinase do?
Break down connective tissue components – facilitate tissue invasion
what does C5a peptidase
do?
inactivates complement component C5a
what do Streptolysins -O and –H do?
Lyse red and white blood cells and platelets
what does Erythrogenic toxin do?
Causes the rash of scarlet fever
how does S. pyogenes avoid phagocytosis
M-protein binds fibrinogen and masks bacterial surface, blocking complement binding and opsonisation
