Infection And Immunity Flashcards
What is an infection?
Invasion of a host’s tissues by microorganisms which case disease through microbial multiplication, release of toxins/virulence factors and/or the host response to infection
Name 3 modes of horizontal transmission of infection (3)
- Contact (direct, indirect, vectors)
- Inhalation (droplets, aerosols)
- Ingestion (faecal-oral)
Which mode of transmission is ‘mother to child’ known as?
Vertical transmission
Describe the 5 stages of how a microorganism establishes within a host (5)
- Exposure (patient, environmental)
- Adherence (stick to body surfaces)
- Invasion (through skin/soft tissue)
- Multiplication (colonisation)
- Dissemination (spread of infection throughout body)
Name 2 ways in which microorganisms can cause damage to the host (2)
- Release of virulence factors (endo/exotoxins)
- Host cellular damage (local inflammation and immune response can damage normal tissue)
What is a virulence factor?
Substance produced by microorganism which can either be secreted (exotoxin) or released during microbial breakdown (endotoxin) which can stimulate host biological pathways
Name 4 ways you could get an infection from the environment (4)
- Water
- Air
- Food
- Surfaces
Give 5 disease determinants between patient and pathogen which may lead to disease (5)
Pathogen: - Antimicrobial resistance - Inoculum size - Virulence factors Patient: - Site of infection - Comorbidities
What questions would you consider to determine whether a patient has an infection? (4)
- Is there an infection? Any symptoms that suggest this?
- Where is the infection?
- What is the cause of infection?
- What are the best treatment options?
Name the 5 steps you would take to determine if a patient had an infection and how you would treat it
- History (symptoms, potential exposures)
- Examination (organ dysfunctions)
- Specific investigations (microbiological)
- Supportive investigations (aid diagnosis e.g. FBC, CRP)
- Baceteriology/Virology (take sample, MC&S, antigen/NA detection)
What are the stages of investigation in bacteriology? (4)
- Specimen sample (swab, tissue biopsy)
- Microscopy (inc. gram stain), culture and antibiotic susceptibility (MC&S)
- Antigen detection
- Nucleic acid detection
Name 3 virulence factors other than toxins which contribute to bacterial pathogenesis (3)
- Enzymes e.g. Collagenase (invasiveness)
- Pili/Fibri (adherence)
- Polysaccharide capsule (host entry)
Name 2 ds envelopes viruses and 2 ds non-enveloped viruses (4)
- Non-enveloped: adenovirus, HPV
- Enveloped: Herpes viruses, hepatitis B
What is a bacteriophage?
Virus which parasitises bacteria and uses their machinery to reproduce and replicate
Give 2 examples of parasites: one single cellular and one multicellular (2)
- Single cellular: Protozoa e.g. Plasmodium falciparum
- Multicellular: Helminths e.g. Schistosoma mansoni (fluke)
Give 2 examples of fungi: one single cellular and one multicellular (2)
- Single cellular: Yeasts e.g. Candida
- Multicellular: Moulds/dermophytes e.g. Ringworm
Define bacteraemia and explain how this differs from sepsis (2)
- Bacteraemia is the presence of bacteria in the blood
- Sepsis is a serious life threatening response to infection
What is septic shock?
Persistent hypotension due to sepsis which requires treatment to maintain blood pressure despite fluid resuscitation
Name 3 ways you could recognise sepsis (3)
- Patient is acutely unwell and/or has a raised EWS
- Clinical features suggesting source e.g. meningitis, pneumonia
- Red Flag Signs - immediate action required (high RR, low BP, unresponsiveness)
How would you treat a patient with sepsis? (6)
WITHIN THE HOUR:
- Give: high flow O2, antibiotics, IV fluids
- Take: blood culture, urine sample, serum lactate
Explain 2 ways in which sepsis can affect the coagulation cascade. What are the consequences of this? (3)
- Release of endotoxins from bacteria leads to the release of cytokines from inflammatory cells (namely macrophages)
- Cytokines stimulate production of thrombin which activates the clotting cascade. They also inhibit fibrinolysis (breakdown of clots) which can lead to microvascular thrombosis and organ ischaemia
- Results in shock/multi-organ failure
What would be your first choice for an antibiotic to treat meningitis and why? (2)
- CEFTRIAXONE
- Able to penetrate into the CSF
Give 3 life threatening complications of sepsis (3)
- Irreversible hypotension (may lead to cardiac arrest)
- Acute kidney injury
- Organ ischaemia/necrosis
What is the effect of a polysaccharide capsule on bacteria?
Prevents phagocytosis of bacteria by inflammatory cells
