Streptococcus pneumoniae

• Streptococcus pneumoniae commonly known as pneumococcus.

• Pneumococcus is a significant human pathogen responsible for infection in adult and elder.

• Pneumococci are normal commensal of the upper respiratory tract.

• They are important pathogen of pneumonia and otitis media in children.

Morphology

• Pneumococci are gram positive bacteria.

• Shape: cocci

• Size: 1 micrometer in diameter

• Motility: non-motile

• Capsule: present

• Present in pass or short chain.

Toxin and other virulence factor

• Pneumococci produce an oxygen labile intra-cellular haemolysin and leucocidin.

• Capsule

• C-carbohydrate antigen: CRP is named after this.

• Pneumolysin

• Autolysin: responsible for bile solubility and draughtsman colony.

Antigenic structure

• The most important antigen of the pneumococcus is capsular polysaccharide, m protein, cell wall carbohydrates.

  1. Capsular polysaccharide: It diffuse into culture media or tissue and infective exudates hence it is also called the soluble specific substance.

  2. M protein: M protein is characteristic for each type of pneumococcus. it is not associated with virulence and antibody to m protein is non-protective.

  3. Cell-wall carbohydrates: pneumococci contain a species specific carbohydrates antigen which is named as c-substance.

Pathogenesis

• Streptococcus pneumoniae is the most common cause of several condition such as lobar pneumonia, pyogenic meningitis in all ages, non-invasive manifestation such as otitis media and sinusitis.

# Source of infection:

Contaminated droplet nuclei, dust

# Mode of transmission:

Through inhalation

# Route of transmission:

Upper respiratory tract

• 90% of children of 6 month to 5 year of age harbor strep. pneumoniae in the nasopharynx.

1. Lobar pneumoniae: Pneumonia result only when the general resistance is lowered.

2. Bronchopneumonia: It is almost always a secondary infection following viral infection of the respiratory tract. Other causative agent responsible for bronchopneumonia include staph. aureus, k. pneumoniae, strep. pyogenes, H. influenza.

3. Meningitis: Most serious pneumococcal infection.

4. Other infection: pneumococcus may also produce pericarditis, otitis media, sinusitis, conjunctivitis, peritonitis, and suppurative arthritis usually as complication of pneumoniae.

# Risk factor:

• Children <2 years

• Splenectomy, sickle cell disease and other hemoglobinopathies.

• Patient with chronic disease such as lungs, heart, kidney, and liver disease etc.

• Viral upper respiratory tract infection. Ex- Influenza

Laboratory diagnosis

• Specimen:

  • Sputum

  • Cerebrospinal fluid (CSF)

  • Pleular exudate

  • Blood

• Collection and transport:

  • All the specimen should be collected in sterile containers under all aspectic condition.

  • In case of delay CSF specimen should never be refrigerated but kept 37°C.

• Direct microscopy and antigen detection:

  • Gram staining of smear reveals a large number of polymorphs and typical organism.

  • In case of meningitis presumptive diagnosis may be made by finding gram positive diplococci which may intra-cellular as well as extracellular in CSF smear.

• Culture:

  • Specimen is inoculated on blood agar incubated at 37°C for 24 hours in the presence of 5-10% Co2.

  • Pneumococci are fastidious organism to grow they require enriched medium (blood agar) to grow.

  • Specimen is culture on Blood agar and chocolate agar and plates are incubated as above.

  • The colonies on blood agar

    • Shape: Dome shape

    • Size: 0.5-1 mm

    • Surface: smooth

    • Edge: entire

    • Elevation: Low convex

• Biochemical reaction:

  • Coagulase: negative

  • Catalase: negative

  • Oxidase: Negative

  • Indole: negative

• Antigenic detection:

  • Urinary antigen test

  • latex agglutination test: used to detect pneumococcal antigen in CSF or other body fluid.

• Molecular method:

  • Polymerase chain reaction

  • Real time PCR

Treatment

• Penicillin G remains the drug of chaise.

• oral amoxicillin is recommended for children with acute otitis media

Prevention

• Vaccination

• Good hygiene