Infection Flashcards by RG Cattermole

What is an infection?

Invasion of a host tissue and multiplication of organisms

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How broadly is disease caused by infection?

By microbial multiplication, toxins, host reponse

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What is virulence?

Genetic, biochemical or structure features that enable an organism to produce a disease

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What is toxic shock?

Fever, hypotension, multisystem organ failure, erythematous rash caused by toxins of esp staph aureus

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What is catalase? What is coagulase? What are they used to differentiate between?

Catalase - enzyme that can convert H2O2 to H2O and O2 to prevent Ros damage of bacteria (virulence)

Coagulase - enzyme that can clot blood - helps prevent neutrophil phagocytosis of bacteria (virulence).

Catalase differentiates between strep and staph (positive)

Coagulase differentiates between types of staph (+ or -)

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What is facultatively anaerobic vs obligate anaerobic?

Will do respiration anaerobically in the absence of O2 but in the presence of O2 will do it aerobically

Obligate anaerobes are poisoned by O2 so do respiration anaerobically only

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What is agar?

General nutrients + 5% sheeps blood useful for cultivating organisms with complex nutritional needs and determining haemolytic properties of an organism

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What is post-infection sequelae? Give an example?

Disease that occurs from prior infection e.g. rheumatic heart disease –> valve problems due to strep pyogenes infection

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What is sepsis vs septic shock??

Life threatening organ dysfunction due to dysregulated host response to infection

Septic shock is persisting hypotension requiring treatment to maintain blood pressure despite fluid resuscitation.

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What is bacteraemia?

Presence of bacteria in the blood +/- clinical symptoms

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What is the sepsis 6 bundle?

Antibiotics (IV)
Fluids
O2
Urine output measurement 
Cultures
Lactate

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How would you determine if someone has an infection?

History - clinical symptoms/history of infection
Examination - physical signs
Investigations - blood tests/cultures etc

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What is supportive care?

Managing the symptoms of the disease but not treating the underlying cause e.g. painkillers/fluids/O2

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What is the human micro biome?

The total number and diversity of microbes living in and on the human body

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Where are you most likely to find human flora?

the skin, eye, and mouth as well as the upper respiratory, gastrointestinal, and urogenital tracts.

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Name 2 common skin flora

Staph epidermis - 90%

Staph aureus

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Name 3 common skin floras of the eye

Staph epidermis
Strep pneumonia
Staph aureus

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Name 2 common mouth/nose flora

Staph epidermis

Staph aureus

Name a common flora of the intestine

Escherichia coli

Name a common flora of the GU tracts (also skin)

Candida Albicans

What are the benefits of human flora?

Compete with pathogens for resources so protect against disease

Some gut bacteria have antimicrobial properties

Can synthesise vit K

Can aid digestion and absorption

What are some potentially harmful effects of normal flora/related to normal flora?

Depletion = allows invasion of pathogens e.g. from antibiotics allows C diff

Over growth of own flora can cause pathology - candida albicans

Can displace from normal site to distant site and cause disease e.g. S epidermis –> endocarditis

Can convert some foods (some sugars) into carcinogens in the gut

What is the model of infection

Pathogen, Patient, Infection, Mechanism of infection, Pathogenesis (Innate/Acquired immunity), Management, Outcome

What three pathogen and three patient factors determine disease progression?

Virulence
Inoculum size
Antimicrobial resistance

Site of infection
Comorbidites
Immune response

What is gram staining? How does it differentiate between bacteria?

Dyeing a collection of cells with different colours/decolouring and the cells will either appear purple or red depending on the components of their cell wall. Purple - gram positive due to their thick peptidoglycan layer in cell wall Red - gram negative due to thin peptidoglycan layer in cell wall

What is the bacterial version of a nucleus?

Nucleoid

What is the difference between fimbrae and pili?

Fimbrae are usually shorter

What do flagella enable?

Bacteria to move in a directional fashion

What is an antigen?

A molecule capable of inducing an immune response on the host organism. Any substance that causes the immune system to produce antibodies against it.

What is an antibody?

Immunoglobulin - large Y shaped protein produced mainly by plasma cells that is used by the immune system to neutralise pathogens such as bacteria and viruses

What 3 things does management (of patient) include?

Diagnosis Treatment Infection prevention

How do you recognise sepsis?

Use early warning score system (basic observations e.g. HR BP resps temp) check for red flags in these observations e.g. unresponsive, high RR low BP etc

What do you do when you find someone has sepsis?

``` Inform senior Dr for review Send urgent investigations Sepsis 6 bundle within an hour Consider early referral to ITU Regular monitoring and reassessment ```

What urgent investigations would you do for sepsis? (8)

``` FBC, U&E EDTA bottle for PCR ?viral? Blood sugar LFTs CRP Coagulation studies Blood gases (venous/arterial) Microbiology - CSF, urine etc ```

Which part of the bacteria triggers inflammation and can lead to septic shock in gram neg?

Endotoxin

How do endotoxins lead to sepsis (6)?

1) Endotoxin binds to macrophages 2) Macrophages release cytokines (TNF-alpha & IL-1) - to stimulate inflammatory response to promote wound repair and recruit RE system 3) Cytokines released into circulation (systemic) 4) Cytokines stimulate growth factor, macrophages and platelets - goal is to contain infection 5) Cytokines lead to activation of humeral cascades and RE system = circulatory insult inc DIC and organ injury 6) Sepsis - infection not controlled

What is the reticulo-endothelial system?

Mononuclear phagocytic system - monocytes and macrophages. Mainly spleen but also in lymph nodes - part of humeral and cell mediated immunity. Important role in defence against bacteria virus fungi protozoa mycobacteria etc etc

How do cytokines initiate the coagulation cascade and microvascular thrombus (3)?

They initiate production of thrombin and thus promote coagulation Cytokines also inhibit fibrinolysis Hence microvascular thrombosis, DIC, organ ischaemia, dysfunction and failure.

What is the major cause of shock and multi organ failure?

Microvascular injury

What are 5 life threatening complications of sepsis?

1) Irreversible hypotension 2) Respiratory failure 3) Acute Kidney Injury (renal failure) 4) Raised intracranial pressure 5) Ischaemic necrosis of digits, hands feet

What would you do microscopy and culture/PCR of CSF for?

Streptococcus pneumoniae, Haemophilus influenzae, and Neisseria meningitidis for meningitis (maybe other things too?)

Why would you do liver function tests in septic patient?

Liver has role in clearing pathogen | Liver can be damaged due to haemodynmic compromise in sepsis (organ failure)

How does sepsis lead to hypotension?

Vasodilation - reduced TPR - inflammatory mediators | Reduced cardiac output

What are spores?

Minute one celled reproductive units of organisms - are thermostable so need to sterilise surgical instruments for spores