Osteomyelitis Infection

Osteomyelitis

• Inflammatory condition of bone and/or bone marrow, usually caused by bacterial or fungal infection
• Can result from:
  • Hematogenous source: infection through bloodstream from a distant site
  • Contiguous source: extension from an adjacent local infection
  • Direct inoculation following trauma

Causes of Osteomyelitis

• Common causes:
  • Staphylococcus aureus (most common)
  • Coagulase-negative staphylococci (S. epidermidis, etc.)
  • Streptococci/Enterococci
  • Pseudomonas aeruginosa
  • Enterobacteriaceae (E. coli, Proteus, etc.)
  • Anaerobic bacteria (Bacteroides, etc.)
  • Mycobacterium tuberculosis
• Less common causes:
  • Brucella species
  • Aspergillus and Candida spp
  • Salmonella spp

Infectious Arthritis

• Infection of one or more joints caused by bacteria, viruses, fungi, and parasites
• Causative organisms:
  • Staphylococcus aureus (most common)
  • Streptococcus pyogenes
  • Streptococcus pneumoniae
  • Hemophilus influenzae
  • Neisseria gonorrhoeae
  • Brucella species
  • Salmonella species
  • Neisseria meningitidis
  • Mycobacterium tuberculosis
  • Bacteroides species
  • Pasteurella multocida

Laboratory Diagnosis

• Evaluation of synovial fluid from the affected joint is the most useful diagnostic test
• Tests include culture, Gram stain, crystals analysis, and white blood cell count with differential

Staphylococcus

• Genus Staphylococcus has at least 30 species
• Coagulase-positive Staph. aureus and coagulase-negative Staph. epidermidis and Staph. saprophyticus

Staphylococcus aureus

• Gram-positive cocci arranged in grape-like irregular clusters
• Non-motile and do not form spores
• Virulence factors:
  • Cell surface adhesins (e.g. fibronectin-binding protein, collagen-binding protein, clumping factor)
  • Enzymes (e.g. catalase, coagulase)
  • Exotoxins (e.g. α-, β-, γ-, and δ-hemolysins, P-V leukocidin)
  • Capsule protects the bacteria by inhibiting phagocytosis

Virulence Factors of Staphylococcus aureus

• Membrane-damaging toxins:
  • α-toxin is the most potent membrane-damaging toxin
• Enterotoxins:
  • 15 enterotoxins (A-E and G-P)
  • Responsible for staphylococcal food poisoning
  • Very heat resistant and resist hydrolysis by GIT enzymes
• TSST-1:
  • Responsible for most cases of Toxic Shock Syndrome
• Exfoliative toxin:
  • Causes the scalded skin syndrome