Pneumococcus – Summary

• Normal inhabitants of upper respiratory tract
• Most prevalent organisms in Pneumonia & Otitis media in children

Morphology & Taxonomy

• Gram +ve
• Diplococci –
  • lanceolate shaped/ flame shaped
  • Slightly elongated cocci, one end rounded & other end pointed
  • Broad ends in apposition
• Differentiating features from other streptococcus
  1. Its morphology – diplococci
  2. Bile solubility
  3. Optochin sensitivity
  4. Specific polysaccharide capsule
• Non motile
• Non sporing
• Readily stained by aniline dyes
• Capsule seen by India ink preparation

Culture

• Grow only in enriched media
• Aerobes, facultative anaerobes
• Growth improved by 5-10% CO2
• Blood agar
  • After 18 hrs – small dome shaped glistening colonies with surrounding green area of α-hemolysis
  • On further incubation – flat colonies with raised edges – doughnut / draughtsman / carrom coin appearance
  • In anaerobic conditions – colonies surrounded by beta hemolysis due to oxygen labile hemolysin O

• Liquid media
  • Uniform turbidity
  • Autolysis of cocci due to intracellular enzymes
• Optochin sensitivity
  • Sensitive to optochin – ethyl hydrocuprein

Epidemiology

• Normal commensal in upper respiratory tract
• Transmission by droplets

Pathogenesis

• Virulence factors
  • Capsule – acidic, hydrophilic, protects from phagocytosis, capsular polysaccharide also called ‘Specific soluble substance'( SSS ), adapts to external environment
    • Also shows Quelling reaction – capsule swells on addition of antisera & methylene blue for visualisation
  • Pneumolysin – secreted cytotoxin, causes cytolysis of cells & tissues
  • Pneumococcal H inhibitor – impedes formation of C3 convertase in complement
  • Pneumococcal surface protein C – binds to factor H & accelerate breakdown of C3
  • Pili help in binding of bacteria to cells

Clinical features

• Asymptomatic/ mild symptoms in initial infection when young
• Spread through blood to distant sites or locally to mucosal surfaces, direct spread to CNS is rare but can occur in skull base fractures
• Non invasive – otitis media
• Invasive – Bacteremic pneumonia, Meningitis
• Pneumonia – mild to life threatening disease
  • Associated with viral upper respiratory tract infection
  • Abrupt onset of cough & dyspnea, rusty sputum
  • Along with fever, shaking chills, myalgias
  • Pleuritic chest pain & significant dyspnea – indicates involvement of parietal pleura
  • High degree of suspicion required
  • Empyema – most common focal complication
• Meningitis
  • Pyogenic
  • Primary or secondary from otitis media, Bacteremia, mastoiditis
  • One of the Most common etiologies of meningitis in children
  • Severe generalized gradual onset headache, fever, nausea
  • CNS symptoms – Stiff neck, photophobia, seizures, confusion along with altered consciousness, Brady cardia, hypertension ( Increased Intracranial pressure )
  • Brudzinski sign, Kernig sign +ve in some adult patients
• Osteomyelitis
• Septic arthritis
• Endocarditis
• Pericarditis
• Peritonitis
• Sinusitis & otitis media – acute, severe pain, fever, deafness, tinnitus
  • Red swollen Tympanic membrane with reduced movement

Lab diagnosis

• Microscopy – gram +ve diplococci
• Culture
• Biochemical tests
  • Catalase & oxidase -ve
  • Hiss serum sugars – fermentation
  • Bile solubility – constant property of Pneumococcus
• Antigen detection – SSS detection in CSF by precipitation
• Biomarkers – CRP
• Mouse inoculation
• Molecular methods

Treatment

• Parenteral penicillin G – drug of choice for susceptible strains
• Macrolides, cephalosporins
• Menigitis – Vancomycin + cefotaxime/ ceftriaxone ; if allergic to ß-lactams, rifampin can be replaced
• Other invasive infections – Penicillin G ; cefotaxime/ ceftriaxone
• For OP management – Amoxicillin/ Levofloxocin
• Acute otitis media – Amoxicillin

Prevention

• Capsular polysaccharide vaccines
  • PPSV23 – 23 valent, T cell independent
• Polysaccharide protein conjugate vaccines
  • PCV – 2 vaccines containing 10 & 13 serotypes available

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