BMS Wk 5 lec 3

Otitis Media (OM)

• Acute Otitis Media (AOM) complications:
  • Acute mastoiditis
  • Meningitis
  • Brain abscesses
• 21,000 deaths from AOM per year
• 30 per 10,000 individuals: hearing loss
• Perforation of tympanic membrane

Otitis Media with Effusion (OME)

• Epidemiology:
  • Incidence and prevalence difficult to establish

Chronic Suppurative Otitis Media (CSOM)

• Epidemiology:
  • Incidence and prevalence difficult to establish

Causal Pathways for Otitis Media

• Eustachian tube anatomy
• Common otopathogens:
  • Streptococcus pneumoniae
  • Haemophilus influenzae
  • Moraxella catarrhalis
  • Pseudomonas aeruginosa

Haemophilus influenzae

• X factor (Hemin) and V factor (NAD+) required for growth
• Virulence factors:
  • Adhesins
  • Polysaccharide capsule
  • Lipid A chains/lipooligosaccharides
  • Fimbriae
  • IgA protease
  • Biofilms

Moraxella catarrhalis

• Gram-negative, diplococcus, aerobic bacteria
• Common in URT, middle ear, eye infections
• Commonly resistant to beta lactam drugs
• Part of normal microbiota of ~3% of people (children more)
• Variable rates of colonization in communities
• Virulence factors:
  • Antibiotic resistance (b-lactamase resistance)
  • Outer membrane proteins (uspA1-A2, Pili)
  • Iron-regulated proteins (transferrin-binding proteins, lactoferrin-binding proteins)
  • Lipid A chains/lipooligosaccharides

Streptococcus pneumoniae

• Virulence factors:
  • Polysaccharide capsule
  • Fimbriae
  • Surface proteins that inhibit activation of complement

Pseudomonas aeruginosa

• Causes otitis externa
• Virulence factors:
  • Fimbriae and adhesins for attachment
  • Formation of biofilms
  • Produces enzymes like elastase, which breaks down elastic fibers and degrades complement system
  • Pyocyanin triggers free radical accumulation, causing tissue damage
• Epidemiology:
  • Found mostly in soil, not a component of regular microbiota
  • Common nosocomial infection agent (10% of hospital infections)

Staphylococcus aureus

• Salt-tolerant, facultative anaerobe, resistant to desiccation, UV radiation, and heat
• Along with Staphylococcus epidermidis, makes up ~90% of skin microbiota
• Common cause of otitis externa
• Virulence factors:
  • Enzymes:
    • Coagulase, Hyaluronidase, Staphylokinase
    • Lipase, beta-lactamase
  • Structural defenses:
    • Capsule/slime layer glycocalyx
    • Binding IgG antibody stem regions
  • Toxins:
    • Cytolytic toxins to disrupt membranes
    • Leukocydin to kill leukocytes
    • Epidermal cell differentiation inhibitors
    • Exfoliative toxins (Toxic Shock Syndrome Toxin)

Other Diseases Caused by Staphylococcus aureus

• Skin diseases
• Reproductive system diseases
• Systemic infections/cardiovascular diseases
• Respiratory system diseases
• Gastrointestinal system diseases