PNEUMOCOCCI

Pneumococci

Morphology

1. Pneumococci are gram-positive cocci that are usually lance-shaped.
2. They are 0.5-1.5 μm in diameter, and 1.5-3.0 μm in length.
3. They have a thick peptidoglycan cell wall and a polysaccharide capsule.
4. The capsule is made of a complex polysaccharide that surrounds the bacterial cell and provides it with virulence.

Virulence Factors

1. The polysaccharide capsule is the main virulence factor of pneumococci.
2. The capsule prevents the phagocytosis of the bacteria by neutrophils and macrophages.
3. Pneumococci also produce several enzymes, including:
   • Autolytic enzyme: breaks down the peptidoglycan cell wall.
   • Hyaluronidase: breaks down hyaluronic acid in connective tissue.
   • Streptokinase: converts plasminogen to plasmin.
   • Cytolysin: lyses red blood cells.
4. Pneumococci also produce several toxins, including:
   • Cytotoxin: kills cells by lysis.
   • Hemolysin: kills red blood cells.
   • Phospholipase: breaks down phospholipids in cell membranes.

Pathogenesis

1. Pneumococci are usually acquired through respiratory droplets or close contact with an infected person.
2. The bacteria enter the lungs through the nasal passages or mouth.
3. The bacteria multiply in the lungs and cause inflammation.
4. The inflammation can lead to:
   • Pneumonia: inflammation of the lungs.
   • Meningitis: inflammation of the meninges.
   • Sepsis: infection of the bloodstream.
5. The bacteria can also spread to other parts of the body, including:
   • Middle ear: otitis media.
   • Sinuses: sinusitis.
   • Bloodstream: bacteremia.

Laboratory Diagnosis

1. Blood cultures: collect a sample of blood from the patient.
2. Sputum cultures: collect a sample of sputum from the patient.
3. Cerebrospinal fluid (CSF) cultures: collect a sample of CSF from the patient.
4. Gram stain: stain the bacteria to identify their shape and Gram reaction.
5. Serotyping: identify the serotype of the bacteria using a specific antiserum.
6. PCR (polymerase chain reaction): amplify specific DNA sequences of the bacteria.
7. Antibiotic sensitivity testing: test the bacteria for sensitivity to different antibiotics.

Clinical Features

1. Pneumonia: cough, fever, chills, and difficulty breathing.
2. Meningitis: headache, fever, stiff neck, and confusion.
3. Sepsis: fever, chills, and difficulty breathing.
4. Otitis media: ear pain and fever.
5. Sinusitis: nasal congestion, facial pain, and fever.

Complications

1. Pneumonia: respiratory failure, sepsis, and death.
2. Meningitis: brain damage, deafness, and death.
3. Sepsis: organ failure, shock, and death.
4. Otitis media: hearing loss and perforation of the eardrum.
5. Sinusitis: nasal congestion, facial pain, and infection of the brain.

Management

1. Antibiotics: penicillin, ampicillin, or other beta-lactam antibiotics.
2. Supportive care: oxygen therapy, hydration, and rest.
3. Ventilatory support: mechanical ventilation for severe pneumonia.
4. Antipyretics: acetaminophen or ibuprofen for fever.
5. Corticosteroids: for severe inflammation.

Prevention

1. Vaccination: pneumococcal conjugate vaccine (PCV) and pneumococcal polysaccharide vaccine (PPSV).
2. Hand hygiene: wash hands frequently to prevent the spread of the bacteria.
3. Avoid close contact: avoid close contact with an infected person.
4. Good ventilation: good ventilation of the environment to prevent the spread of the bacteria.
5. Antibiotic stewardship: use antibiotics judiciously to prevent the development of antibiotic-resistant bacteria.