11. Virulence Factors Flashcards
Define ‘commensal’
an organism that lives in harmless association with it’s host
Define ‘colonisation’
sustained presence of an organism at a body siteD
Define ‘pathogen’
an organism that can cause disease in otherwise healthy individuals
Define ‘carriage/carrier state’
- colonisation with a pathogen
- i.e host can act as source of infection for others but shows no symptoms themselves
Define ‘opportunistic pathogen’
an organism which requires the host to have pre-existing defect in its defences before it can cause disease
Define ‘infection’
growth of a non-native microorganisms at body site
- with or without damage to host
Define ‘virulence’
measure of capacity of an organism to cause diseasee
Define ‘virulence factors’
properties of bacterium which contribute to its virulence
Methods of transmission
- body fluids
- insects
- skin to skin
- accident
Define ‘endogenous infections’
- ones caused by infectious agent already present in body
- has been previously inapparent or dormant
Define ‘exogenous infections’
acquired from sources outside of patients
4 examples of virulence factors
- adhesins
- invasins
- toxins
- extracellular enzymes
Why do bacteria have virulence factors?
- part of their survival strategy
- allows multiplication in host
What disease is caused by bordetella pertussis?
hooping cough
What disease is caused by neisseria gonorrhoeae?
gonorrhoeae
What disease is caused by yersinia pestis?
plague/black death
What disease is caused by bacillus anthracis?
anthrax
List 3 opportunistic pathogens and what they cause?
- staphylococcus epidermidis (endocarditis and issues in catheters)
- pseudomonas aeruginosa (infects burns)
- escherichia coli (diarrhoea)
Stages of infection
- exposure to pathogen
- adherance to skin or mucous
- invasion through epithelium
- infection (growth and production of virulence factors and toxins)
- toxicity (local and systemic effects) and invasiveness (further growth at original sites and distant ones)
- causes tissue damage and disease
Explain adherance of disease
- initial attachment involves interaction between surface structure of bacteria and host tissue
- bacteria surface is pili, fimbriae, surface proteins
- host tissue receptors are glycoproteins, tissue-specific antigens
How does E.Coli adhere?
- with type 1 pili
- adhere to epithelial cells in urinary tract
How does vibrio cholerae adhere?
- highly mobile
- swims through intestinal mucus and attaches to receptors in gut wall
List innate host defence against infection
- skin
- flushing
- secretions
- mucous membranes
- normal bacterial population
List adaptive host defence against infection
- phagocytosis
- inflammation, fever
- antibodies
How does skin defend against infection?
- keratinsases
- skin penetration
How does flushing defend against infection?
- adherance
- motility
How does secretions defend against infection?
- lysozyme resistant walls
- tolerance to salts, bile, pH etc
How does mucous membranes defend against infection?
- degrade
- or swim
through mucin
How does commensal flora/normal bacteria defend against infection?
- metabolic end products
- bacteriocins
- bacteriophage
How does phagocytosis defend against infection?
capsules
How does inflammation/fever defend against infection?
heat shock response
How does antibodies defend against infection?
- breakdown of immunoglobins
- kill host defence cells
- intracellular growth
- antigenic variation
Explain invasion in infection
- invasion into bloodstream - bacteraemia
- infection in blood is septicaemia
- after attachment, some bacteria invade epithelial cells
Disease arises from infection when …
- damage to host occurs
- infection is just the introduction of a microorganism that isnt a natural coloniser
For growth, bacteria must obtain what?
- nutrients (inc. trace metals like iron)
- correct oxygen environment
Explain invasion/spreading of infection
- through lungs, gut, urinary tract, blood
- via sinuses and body cavities
- tracks along nerve pathways from cell to cell
- causes tissue breakdown
2 types of toxins
- endotoxins
- exotoxins
3 tissue-degrading enzymes
- collagenase
- hyaluronidase
- haemolysin
1 example of an endotoxin
lipopolysaccharide
Explain LPS as an endotoxin
- found in gram negative bacteria in the outer layer of the outer membrane
- released in growth or when bacteria die and lyse
- causes fever, septic shock and local inflammation
Exotoxins are secreted by … and are produced by …
They are stable/unstable
Toxic/non-toxic?
- bacteria
- some gram pos and neg bacteria species
- relatively unstable (heat-sensitive)
- highly toxic (1 nanogram of botulism toxin can be fatal)
Examples of exotoxins and their effects
- tetanus attacks nervous system and causes lock jaw
- botulism attacks motor nerve causing paralysis
- diphtheria stops cell protein synthesis
Damage from exotoxins doesn’t always need bacterial infection. Example of this?
- preformed staphylococcal enterotixon in food
- causes rapid onset food poisoning
- antibiotics are useless and vaccines need to target toxin rather than infectious agent
What bacteria causes tetanus?
clostridium tetani
Tetanus bacteria is gram … and a … rod
Found in …
How does it cause disease?
Symptoms
- positive
- spore forming
- soil and animal faeces
- secretes a powerful neurotoxin that blocks release of neurotransmitters from presynaptic membranes of inhibitory nerve synapses
- lockjaw, muscular contraction
Botulism is linked to what bacteria?
It’s found where?
How to inactivate toxin?
- clostridium botulinum
- soil, water, foodstuffs like honey
- extremely potent inactivated by cooking
- tinned foods undergo a botulinum cook at 121 degrees celc for 3 mins
How is botulinum toxin used?
- for botox
- treats muscle conditions
- removes wrinkles by temporarily relaxes muscles
- and for murder (poison tip umbrella assasination of Markov)
Bacteria between diphtheria?
Where is gene carried?
What does it do?
How to stop it?
- corynebacterium diphtheriae
- carried on bacteriophage
- inhibits proteinsynthesis
- vaccine based on inactivated toxin is highly effective
Explain necrotising fasciitis?
- rapidly spreading
- tissue destruction by toxins which initiate an overactive immune response
- can be single organism or polymicrobial (most common are streptococcus pyogenes or MRSA)
- treatment by surgical debridement
Explain resolution in infection
- for acute it’s a short duration (days)
- for chronic longer (weeks to months)
Example of a chronic lung condition
- TB
- can show granuloma on scans where infection is controlled but not resolved
Factors that increase susceptibility to disease
- trauma (accidental or intentional like surgery)
- underlying disease (HIV immunosuppression etc)
- age
- genetic constitution
- nutrition
- hormonal factors and stress
- pollutants
