Osteomyelitis TP Flashcards

1
Q

Route of infection

A
  • Trauma (joint replacement, root canal treatment, etc)
  • Spreading from local area of infection (e.g. SSTI, diabetic ulcer)
  • Hematogenous route (bacteremia)
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2
Q

Risk factors

A

• Diabetics with foot ulcers
• Patients with infections following trauma, bone
surgery, joint replacement
• Root canal treatment

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3
Q

Pathogenesis

A
  1. Bacteria infect bone (colonise and proliferate)
  2. Leukocytes infiltrate infected site and fight
    bacteria
  3. Inflammation and formation of pus
  4. Devascularisation, dead bone, abscess
  5. Bacteria might invade bone cells and evade
    immune response and drugs (possible chronic
    osteomyelitis)
  6. Bacteria might spread to joint (septic arthritis)
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4
Q

Pathogens

A
  • Staphylococcus aureus (most common cause, ~80% of osteomyelitis cases in children and young adults )
  • Streptococcus pyogenes (Group A Streptococcus)
  • Group B Streptococcus (mainly in infants)
  • Hemophilus influenzae
  • Enterobacter spp.
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5
Q

Diagnosis (3)

A
  • Radiology (X-ray, MRI, CT)
  • Bone biopsy
  • Blood sample (if associated with bacteremia)
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6
Q

Staph aureus

A

• Habitat: anterior nares (~20% of people are asymptomatic carriers), transient carriage on skin
• Transmission: human-to human
• Source of infection: community and hospital
(one of the most common nosocomial infections)
• Diseases: skin and soft tissue infections,
invasive disease, toxic shock, etc

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7
Q

How does SA cause an infection

A
  1. crack in skin
  2. splinter
  3. hair
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8
Q

Virulent factors (3)

A
  1. Adhesins - binding/colonisation
  2. Immune evasion factors - neutralisation of immune response
  3. Spreading factors - proteases, DNAses, HAse
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9
Q

Spreading factors (4)

A
  1. Staphylokinase (fibrinolysin): causes fibrinolysis, dissolves fibrin clots
  2. Lipases: hydrolyse lipids
  3. DNases: hydrolyse DNA (released from dead leukocytes), decreases viscosity of purulent material
  4. Cytolysins: destroy epithelial cells!
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10
Q

Immune evasion factors (5)

A
  1. Cytolysins
    e.g. hemolysin, leukocidin
    kill erys, leukocytes, tissue cells
  2. Capsule
    thick layer outside the cell wall, prevents opsonisation and phagocytosis (=immune evasion)
  3. Slime layer, extracellular polysaccharide (EPS)
    • microbial community with bacteria attached to a substrate or interface or to each other, embedded in a matrix of extracellular polymeric substance!
    • Immune evasion, antibiotic tolerance
  4. Protein A:
    binds IgG (except IgG3) in “wrong orientation” (via Fc region), prevents opsonisation and phagocytosis.
  5. Cell bound coagulase (clumping factor)
    binds prothrombin and induces fibrin polymerisation, fibrin deposition on cell surface prevents opsonisation and phagocytosis
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11
Q

Superantigens

A
  • family of heat-resistant secreted proteins (>20 members)! - non-specific, highly potent T cell mitogens!
  • trigger strong pro-inflammatory immune response (IL-1”, TNF-!,!
    IFN-#)!
  • synergistic effect with endotoxin (LPS) !
  • systemic inflammation with tissue destruction, vascular leakage, !
    multiorgan failure, toxic shock!
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12
Q

Treatment/therapy

A

• Prolonged antibiotic treatment (weeks to months),e.g. PIC line, empirical treatment until organism is known
! Note: ~90% of S. aureus are resistant to penicillin
! ~30% of S. aureus are methicillin-resistant (MRSA)
! Increasing resistance to other antibiotics
! Vancomycin often used as last option for MRSA (not
for MSSA to avoid rise of vancomycin-resistance)

• possibly surgical debridement

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13
Q

beta lactam resistant penicillins

A
  1. oxacillin
  2. flucloxacillin
  3. methicillin (prototype)

OR

penicillin with betalactamase inhibitor

ie amoxicillin + clavulanic acid = augmentin

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14
Q

Other disease caused by SA (11)

A
  1. impetigo
  2. Folliculitis
  3. Furuncle
  4. Carbuncle
  5. Staphylococcal Scalded Skin Syndrome (Ritter’s disease)
  6. Cellulitis
  7. Septic arthritis
  8. Acute infectious endocarditis
  9. Bacterial Pneumonia
  10. Necrotising fasciitis (flesh-eating disease)
  11. Toxic Shock Syndrome!
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