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
Which bacterium is mainly responsible for causing meningitis? What would its appearance be microscopically? (2)
- Neiserria meningitidis
- Gram -ve (red stained) diplococci (mainly serogroup B) visible in CSF
Give 2 preventative measures for meningitis (2)
- VACCINATION (meningococcal C conjugate, serogroup B etc.)
- ANTIBIOTIC PROPHYLAXIS (people in close contact)
How is meningitis spread?
Aerosols/nasopharyngeal secretions
Give 2 consequences of disseminated intravascular coagulation (DIC) (2)
- Tiny clot formation throughout the cardiovascular system which may lead to organ ischaemia
- Inability to clot when required (as clotting factors are used up) which may lead to bleeding
Describe the general classification of Antimicrobials (4)
- Antibacterials
- Antivirals
- Antifungals
- Antiprotozoal
Give 3 ideal properties of antimicrobials which can increase patient compliance (3)
- Ease of administration e.g. oral/IV (normally both)
- Few adverse side effects
- Long half life (infrequent dosing)
Why is it ideal that antimicrobials are ‘selectively toxic’?
Minimally toxic to host but very toxic to pathogens
What are the main mechanisms of action of antimicrobials? (4)
- Target cell wall synthesis
- Target cell membrane function
- Target nucleic acid synthesis
- Target protein synthesis
Explain 3 mechanisms of resistance to antibiotics by bacteria (3)
- Production of drug inactivating enzymes
- Altered uptake of drug (decreased permeability or increased efflux)
- Altered targets e.g. target enzyme has a lower affinity for drug
Describe 2 ways in which the gene for antimicrobial resistance can be spread to other bacteria (2)
- Chromosomal mutation (bacteria with mutation will multiply asexually so entire population has the mutated gene)
- Horizontal gene transfer (through conjugation, transduction or transformation)
Describe 3 methods of horizontal gene transfer in bacteria (3)
- Conjugation (fusion via sexual contact and transmission of genetic material)
- Transduction (through bacteriophage)
- Transformation (free DNA passed directly through cell wall)
Describe 2 methods of measuring antibiotic activity (2)
- Disc sensitivity testing (discs soaked in various antimicrobials are placed on a agar; larger circumference=more effective)
- Minimum inhibitory concentration
Explain the pathogenesis of infections in surfaces (4)
- Adherence of pathogen to host cell or prosthetic surface
- Biofilm formation
- Invasion and multiplication
- Host response (pyrogenic, granulomatous etc.)
What structure on bacteria allow adherence to surfaces?
Pili/fimbriae
