Properties

Pathogenesis

Clinical findings

Laboratory diagnosis

Treatment & Prevention

Streptococcus pneumoniae

Gram-positive cocci

Nonmotile

Do not form spores

Arranged in chains or pairs.

Catalase negative.

Form a green clear zone around their colonies due to incomplete lysis of red cells.

Polysaccharide capsules which swell (quellung reaction)

Lysed by bile or deoxycholate.

Growth inhibited by optochin.

Transmission:

- not regarded as part of normal flora.

- frequently carried in the throat.

- spread in respiratory droplets.

Antiphagocytic capsule interfere with phagocytosis & favor invasiveness.

Pneumolysis is a membrane-damaging toxin.

Produce IgA protease that enhance ability to colonize mucosa of upper respiratory tract.

Multiply in tissues & cause inflammation.

When they reach alveoli, there is outpouring of fluid, red & white cells, resulting in consolidation of the lung.

Diseases:

- pneumonia

- bacteremia

- meningitis

- otitis

- sinusitis

- purulent bronchitis

Complications:

- seeding of bacteria to joints and percardium.

- empyema & lung abscess.

Predisposing factors:

- alcohol

- drug intoxification

- cerebral impairment & suppression of cough reflex

- abnormality of respiratory tract leading to pooling of mucus & bronchial obstruction.

- splenectomy.

- sickle cell anemia

- pulmonary congestion/heart failure.

- trauma to head causes leakage of spinal fluid through nose.

Pneumonia:

- begins with a sudden chill.

- fever

- cough

- pleuritic pain.

- sputum is red or brow color.

Sputum culture: gram stain reveals many pneumococci.

Meningitis: CSF & blood cultures.

Pneumococci forms characteristic draughtsman colonies: a raise rim & sunken in the middle.

Susceptible to penicillin & erythromycin.

Prevention:

- pneumococcal vaccine.

- contains purified polysaccharide capsule from 23 different strains of pneumococci.

Viridans & other oral streptococci

Part of normal flora of mouth: S.oralis, S.mitis

Play a role in dental caries.

Easily enter bloodstream after dental treatment or during normal activities like chewing – settle on heart valve to cause bacterial endocarditis.

Signs: fever, anemia, heart murmur, embolic events.

Benzylpenicillin & gentamicin

Anginosus group

Three species: S.anginosus, S.constellatus & S.intermedius.

Found in normal mouth & gut flora.

Cause dental, brain and abdominal abscesses & endocarditis.

Peptostreptococci participate in mixed anaerobic infections of the abdomen, pelvis, lungs & brain.

Penicillin.