Osteomyelitis

Question 1

What is osteomyelitis

Answer 1

Infection/inflammation of the bone or bone marrow

Question 2

Route of infection for osteomyelitis

Answer 2

Trauma: Deep tissue injury, artificial, root canal treatment
Spread from local infection: Diabetic ulcer, cellulitis, septic arthritis
Hematogenous route: Bacteraemia

Question 3

Pathogenesis

Answer 3

Bacteria infect and proliferate in bone
Leukocytes invade to fight infection
Pus formed
Bone devascularisation, dead bone (sequestrum) and abcesses
Possibility of chronic form
Could spread to joint to cause septic arthritis

Question 4

Osteomyelitis risk groups

Answer 4

Diabetic ulcers; infections following trauma or surgery; root canal; SSTI; following chicken pox (rare)

Question 5

Common causes

Answer 5

• 80% staph aureus
• GAS
• GBS in infants
• Hemophilus influenzae; enterobacter etc

Question 6

Diagnosis

Lab diagnostic

Answer 6

Radiology (x-ray, MRI, CT)
Try avoid Bone biopsy blood sample if with bactaraemia

• Gram staining (positive has large peptidoglycan on top of membrane, negative have an outer membrane)
• Staph has grapelike clusters
• +ve catalase test and aureus has a +ve coagulase test

Question 7

Reminder on diagnostic testing

Answer 7

GRAM POSITVE: Staph or strep
Catalase positive: Staph
Catalase -ve: Strep

Coagulase +: Aureus
Coagulase -: S. Epidermitis

Hemolysis a: strep pneumoniae
Hemolysis b: GAS
hemolysis y: enterococcus

Question 8

Staph Aureus Virulence factors

• Adhesins (_____)
• Immune evasion factors: _____ (kills cells); _____ (prevents _____ with ____ or Ig and phagocytosis); _____, a film of polysaccharides etc to protect from immune factors; ______ _, binds IgG in wrong orientation via Fc stopping opsonisation etc; CELL BOUND ______, binds prothormbin, induces fibrin formation masking cell from opsonisation etc (____)
• Spreading factors: _____, ______* (fibrinolysin, lipases, cytolysins

Answer 8

• Adhesins (MSCRAMMs)
• Immune evasion factors: CYTOLYSINS (kills cells); CAPSULE (prevents opsonisation with C3b or Ig and phagocytosis); BIOFILMS, a film of polysaccharides etc to protect from immune factors; PROTEIN A, binds IgG in wrong orientation via Fc stopping opsonisation etc; CELL BOUND COAGULASE, binds prothormbin, induces fibrin formation masking cell from opsonisation etc (CIF-A)
• Spreading factors: DNAases, staphylokinases* (fibrinolysin, lipases, cytolysins

Question 9

Staph aureus and superantigens (4th virulence)

Family of ____ _____ secreted proteins
Non specific, highly potent _ ___mitogens
Trigger strong _________ response, causing overload on ____, ____ inflammation, tissue destruction, vascular leakage and toxic shock.

NB LPS an endotoxin, can work synergistically

Answer 9

Family of heat resistant secreted proteins
Non specific, highly potent T cell mitogens
Trigger strong pro-inflammatory response, causing overload on cytokines, systemic inflammation, tissue destruction, vascular leakage and toxic shock.

NB LPS an endotoxin, can work synergistically

Question 10

Staph aureus treatment

Answer 10

Prolonged antibiotic treatment, not penicillin as 90% are resistant (due to B lactamase gene)
Now 30% are methicillin resistant (MRSA)
Use vancomycin for MRSA, not MSSA. MRSA form new transpeptidase not inhibited by penicillin

Use b-lactam resistat penicillins: methicillin so clinically flucloxacilin, oxacilin OR a penicllin with b-lactamase inhibitor e.g amoxycillin + clavulanic acid= AUGMENTIN

Question 11

Other disease caused by staph aureus (6)

Answer 11

• Impetigo/pyoderma: prevent with good hygiene, treat with soap water, topical antibiotics/ointments (mupirocin)
• Folliculitis, can lead to a boil (furuncle) leading to a carbuncle which ca leads to systemic spread. Treat with antibiotic creams , flucloxacillin, augmentin
• Cellulitis: dermis/subcutaneous tissue. Area tender warm, eryhtematous, no sharp demarcation
• Septic arthitis, IV antibiotics, analgesia, aspiration
• Acute infectious endocarditis. Chronic or subacute streptococci
• Bacterial pneumonia called necrotizing, staph pnemuoniae more common

Question 12

Staphyloccal scalded skin syndrome

Answer 12

Affects neonates, formation of large cutaneous blisters due to exfoliative toxins.

Question 13

Toxic shock syndrome

Answer 13

Caused by superantigen producing strains
Menstrual TSS: TSST (only one that can penetrate mucosal barrier) due to prolonged use of expandable tampon
Non-menstrual: Growth of TSS strain in wound. Toxins are released in blood causing systemic disease with fever, hypotension etc