L3 Flashcards
(14 cards)
Define: Infection Colonisation Pathogen Commensal Symbiosis Parasite
Infection: organism enters body increasing in number and damages the host
Colonisation: The organism lies on us but does not cause infection (usually outside the host).
Pathogen - Evades immune defences of human host causing infection. Colonisation occurs before infection.
Commensal: Someone who eats with you. Organism lives on/in us w/o causing infection.
Symbiosis - Mutual benefit
Parasite - Host/organism relationship is not mutual. E.g. parasitic relationship of pneumonia bacteria.
What is the diff between professional and opportunistic pathogens?
What is virulence?
Professional Pathogens - Almost always cause disease
Opportunistic pathogens - only cause disease in immunocompromised patients
This is because organisms vary in..
Virulence: fundamental properties of the organism
What is the spectrum of virulence?
How like a organism is to be a pathogen. From commensal to pathogenic.
What determines whether a germ on a patient is pathogen or commensal?
Immune status
Site in question
Virulence of bacteria
Where is staphylococcus aureus found?
Why is it called staphylococcus?
What is its composition on agar?
Commensal of anterior nares in the nose.
Staphylococcus = bunches of grapes in greek.
On agar it makes golden colonies of gram positive cocci in clusters.
How is staphylococcus aureus adapted to be virulent?
Range of virulence factors expressed at surface and some excreted.
Surface expressed proteins secreted to environment.
Capsule (polysaccharide coat) prevent innate arms of immune system recognising and clearing.
Surface proteins w binding sites so it can adhere to diff tissues in the body and gives it diff properties by using host proteins and binds antibodies the wrong way round to “cloak” from immune system.
Contains coagulase causes clotting and stops WBC getting near to kill.
What are 3 staphylococcal toxins?
Cytotoxins: Pore forming, lyse the host cell
Exfoliative toxins: Proteases, target epidermal structural proteins
Enterotoxins: Stim massive T cell activation.
Ingestion leads to vomiting
Many of these are phage encoded - only present on a number of strains.
S.aureus is a normal commensal, when is it not?
Pathogen in skin
Surgical site infection
Vascular line related infections
Bacteraemia - infection almost anywhere e.g. endocarditis, osteomyelitis, septic arthritis
How are lipopolysaccharides recognised?
Innate immune system is sensitive to LPS and endotoxins due to gram negative bacteria predominance.
LPS interacts with Toll-Like Receptors (TLR4) on monocytes/macrophages and endothelium.
This leads to activation of inflammatory pathways, coagulation and clotting pathways and changes in endothelial integrity.
How are peptidoglycans on gram positive recognised differently to LPS?
Don’t have endotoxin, cell wall components of lipoteichoic acid + peptidoglycans can but can stimulate immune response like LPS just on different TLR (Toll-Like Receptors)
What is the glass test used for?
Rashes which should be non-blanching to prove meningococcal septicaemia. This is a medical emergency..
The rash will remain unchanged and will not blanch, or the skin colour will not change.
What does meningococcal pathogenicity contain to be virulent?
Adhesin for respiratory epithelium and the meninges.
Lipopolysaccharide
Capsule
How does streptococcus pneumoniae cause virulence?
How does it cause disease?
Adhesion for respiratory mucosa
Pneumolysin: binds host cell membrane cholesterol
Forms pores + lyses in ciliated cells
Lyses host phagocytic cells
Secretes IgA protease to break down immunoglobulin A preventing mucosal clearance
Capsule: Polysaccharide coat prevents complement-mediated phagocytosis. Specific antibodies to capsule required.
Most common form of pneumonia (40%). A disseminated disease, bacteraemia, endocarditis, upper resp tract infections: sinusitis, otitis media.
Clostridium difficile - what is it?
C.tetani, C.botulinum, C.welchii = Tetanus, Botulism, Welchi.
Gram + rods.
Anaerobic
Spore forming: soil, gut.
Wound/GI infections.
Can become colonised as commensal in the gut, when antibiotics given can cause toxins = diarrhoea