MFD.10 Flashcards
How do bacteria cause disease:
1) Pathogen
2) Opportunistic pathogen
3) Infection
• PATHOGEN: An organism that causes disease in otherwise healthy individuals
• OPPORTUNISTIC PATHOGEN: An organism which requires the host to have a pre-¬‐existing defect in its defences before it can cause disease
• INFECTION: Growth of a non-¬‐native microorganisms at a body site, with or without damage to the host
•
How do bacteria cause disease:
1) virulence
2) virulence factors
VIRULENCE: a measure of the capacity of an organism to cause disease
• VIRULENCE FACTORS: properties of a bacterium which contribute to its virulence
What are the 2 types of infection?
1) Endogenous
2) Exogenous
Define Endogenous infections:
are caused by an infectious agent that is already present in the body, but has previously been inapparent or dormant
Define endogenous infections:
are caused by an infectious agent that is already present in the body, but has previously been inapparent or dormant
Define Exogenous infections:
are acquired from sources outside the patient
Pathogens possess a range of virulence factors. Name them:
– Adhesins
– Invasins (enter cells )
– Toxins
– Extracellular enzymes
What are the stages of infection?
1) Exposure
2) Adherence
3) Invasion
4) Infection
5) THEN..
Toxicity: toxin effects are local or systemic
OR
Invasiveness: Further growth at original and distant sites
6) Tissue Damage, disease
Adherence
Initial attachment involves interaction between surface structures of bacteria and host tissue. What structures are used to do this?
- Bacterial surface structures -¬‐ pili, fimbriae, surface proteins
- Host tissue receptors —glycoproteins, tissue— specific antigens (HLA etc.)
What are the innate ways the host defends itself from pathogens?
- Skin (keratinised, shedding of outer layers)
- Flushing (saliva, urine, peristalsis in gut)
- Secretions (lysozyme, stomach acid, bile salts)
- Mucous membranes (cilia)
- Normal bacterial population (colonisation resistance)
What are the adaptive ways the host defends itself from pathogens?
- Phagocytosis
- Inflammation, fever
- Antibodies
Explain how bacteria evade the following adaptive immune responses:
1) Phagocytosis
2) Inflammation/fever
3) Antibody
Phagocytosis: Capsules (prevent antibody attachment enabling phagocytosis)
Inflammation/fever: Heat shock response (lets them survive the higher temperature)
Antibody: Breakdown of immunoglobulins, kill host defence cells, intracellular
What are commensal flora?
friendly bacteria, provide us with benefits
How do bacteria evade normal bacterial population/ commensal bacteria?
Metabolic end products, bacteriocins, bacteriophage etc
What is bacteraemia
• Invasion into bloodstream
What is septicaemia.
• Infection in the bloodstream
What is the name given to the following definition:
• Invasion into bloodstream
bacteraemia
What is the name given to the following definition:
• Infection in the bloodstream
septicaemia.
Following attachment after invasion, what do the bacteria then do?
invade epithelial cells
Compare the terms infection and disease:
- Infection is a situation when a microorganism that is not a natural (commensal) coloniser grows within the host, whether or not it causes damage.
- Disease arises when there is damage to the host.
How can the bacteria spread once within the cells of a host?
- Through lungs, gut, urinary tract, blood
- via sinuses and body cavities
- Tracking along nerve pathways
- Direct cell-¬‐to-¬‐cell
- Tissue breakdown
Give the 2 types of toxins ( a microbial virulence factor):
1) endotoxin
2) exotoxin
Give the 3 types of tissue-degrading enzymes( a microbial virulence factor):
- collagenase
- hyaluronidase
- haemolysin
Give an example of an endotoxin found only in gram-negative bacteria:
LPS
What is LPS
an endotoxin found only in gram-negative bacteria:
Where is LPS present in gram-negative bacteria?
2) When is it released?
3) What does it cause in the host?
1) outer layer of the outer membrane
2) released during growth or when bacteria die and lyse
3) fever, septic shock and local inflammation
How are they released?
2) What type of bacteria produce them (gram)?
3) Describe its stability and toxicitiy?
1) Secreted by bacteria
2) + and -
3) relatively unstable and highly toxic
Damadge by exotoxin does not require a bacterial infection, so how would it be treated?
2) What would we normally do and why doesn’t it work?
1) vaccines given that target the toxin
2) give antibiotics that target the infectious agent i.e. the bacterium therefore useless
What bacteria causes very swollen pseudomembranes in the posterior pharynx? ( so swollen can obstruct airways)
2) What is the vaccine based on?
3) What carries the toxin? what does the toxin do?
Diphtheria
2) inactivated toxin
3) bacteriophage, inhibits protein synthesis
Why do we cook tin foods to 121 degrees?
2) Descibe bacteria’s toxin’s potency?
to protect against botulism (Clostridium botulinum )
2) very high
What is a symptom of tetanus?
2) How does Clostridium tetani cause this?
1) muscule contraction (e.g. lockjaw)
2) Secretes a powerful neurotoxin that blocks the release of neurotransmitters from the presynaptic membranes of inhibitory nerve synapses
What is the name given to the disease that produces a toxin that causes tissue destruction?
2) How does it do this?
3) Is it an organism or organisms that cause it? +e.g. *2
4) treatment?
1) Necrotising Fasciitis
2) toxin initiates an overactive immune response
3) Can be single organism or polymicrobial
– Most common monoinfections are Streptococcus pyogenes and MRSA
4)surgical debridement
chronic vs acute infection
- Acute infection: short duration (days).
* Chronic infection: long duration (weeks to months).
What factors influence susceptibility to disease?
- Trauma
- Underlying disease or other infections
- Age
- Genetic constitution (tissue type etc)
- Nutrition
- Hormonal factors and stress
- Pollutants
Give examples of trauma that would increase susceptibility to disease: (2)
– accidental (wounds, burns)
– intentional (surgery)
Give examples of underlying disease or other infections that would increase susceptibility to disease: (2)
– e.g. viral infections increase risk of bacterial pneumonia;
- HIV immunosuppression increases other infections
