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Strept.pnumonia

Pneumococci are involved chiefly in upper and lower respiratory tract infection, and is the most frequent bacterial cause of lobar and bronchopneumonia. They also associated with meningitis, conjunctivitis, peritonitis, arthritis, and septicemia. Death might occur if there is delayed in the diagnosis and early treatment.

  The Pneumococcus is part of the normal naso and oropharyngeal flora of many healthy persons which remain harmless, unless it is provoked by a viral infection such as influenza or the common cold to spread to the lower respiratory tract, middle ear, a paranasal sinus or the blood. In this situation Pneumococci are secondary pathogens, but they have an important role as primary pathogens in immunocompromised persons or in unconscious patient due to stroke or trauma to the head leads to aspiration of the contaminated secretion from upper respiratory tract. Pneumococci can also be a primary cause of acute lobar pneumonia in previously healthy persons.

In primary cultures on blood agar, the colonies of Pneunococci most closely resemble those of Strep.viridence. So it must be carefully distinguished between them as fallows: 

 Morphology and identification

 A-Typical organisms:* are gram –positive, lancet-shaped diplococci, are often seen in specimens of young cultures. In sputum or pus, single cocci or chains are also seen. With increasing age the organisms will rapidly become gram-negative, and tent to lyse spontaneously. *Autolysis ofPneumococci is greatly enhanced (i.e. occurs with few minutes) by surface –active agents like ox bile (10%), or sodium deoxycholate 2% is added to a broth culture, or suspension of organisms at neutral PH (bile solubility test).

*Pneumococci are highly sensitive to killing by optochin disc (ethylhydrocurein hydrochloride) on solid media, e.g.at a concentration of 0.001%, nearly a hundred times less than are effective against other streptococci. It is the most reliable simplest test for distinguishing them from Strep. viridence.

*Animal pathogenicity: most but not all strains from infective conditions in man are virulent for the mouse, and in so distinguish from Strep.viridence (which is not virulent). The intraperitoneal injection of a small dose of Peumococci generally causes peritonitis, septicemia, and death of the mouse with in 18-48 hours.

*capsule swelling test with animal pathogenicity are important identifinging tests of pathogenicity.

* Most Peumococci strains are highly sensitive to benzyl penicillin, amoxicillin, cephalosporin, erythromycin and cotrimazole.

B-Culture Peumococci form a small round colony, at first dome-shaped, and later develops a central plateau with an elevated rim. Peumococci are ?-hemolytic on blood agar. Growth is enhanced or best by 5-10% CO2.  it is aerobic and facultative anaerobic. Optimum temperature for growth is 37 ?C. growth on ordinary media , but better on media with 5-10% serum ,blood ,or heated blood.

C- Growth characteristic: Most energy is obtained from fermentation of glucose; this is accompanied by the rapid production of lactic acid, which limits its growth. Neutralization of broth cultures with alkali at intervals results in massive growth.

 D-  Variation: large mucoid colonies are produced by pneumococcal isolates, that produced large amounts of capsules. But capsule production is soon lost on repeated subculture which however again might reproduced and become virulent.

Antigenic characters

* Some 83 serotypes of   Peumococci are distinguished by difference in the nature of the polysaccharide antigen that composes their capsules, and is partly secreted into the culture medium in the form of loose slime, or specific soluble substance.

* The somatic portion of the Peumococci contains on M protein that is characteristic for each type and a group specific carbohydrate that is common to all Peumococci.

Pathogenesis:

 Peumococci producing a disease through their ability to multiply in the tissue, not producing toxin. The virulence of this organism is depending on the presence of the capsule which prevents or delayed ingestion by phagocytes, but it can be killed by the presence of type specific antibodies and natural resistance. The normal respiratory mucosa possesses great natural resistance to the Peumococci, since 40-70% of humans are at some time carriers of virulent Peumococci. But this natural resistance might be lost due to many causes as follow:

1-diseases of respiratory tract that might damage surface cells, accumulation of mucus, or disturbing its mucocilliary functions.

2-alcohol or drug intoxication.

3-malnutrition, sickle cell anemia and immunodeficiency.

4-loss of consciousness, stroke or trauma to the head.

Laboratory diagnosis of peumococcal infections: 

  Diagnosis is generally done by demonstrating the presence of Peumococci in a specimen of sputum, lung aspirate, pleural fluid, cerebrospinal fluid, urine or blood by; a-gram-stained film b-culture on blood agar and incubation in CO2 on a candle jar c- identifying the culture in an optochin sensitivity test

Note 1: all this approach should be done before starting the patient with antibiotic therapy.

Note 2: there is little difficulty in detecting a Peumococcus by culture and recognizing its pathogenic significance when it is present as sole organism in a specimen of blood, csf, or exudates fro a site, such as joint or the middle ear, not normally containing commensal bacteria, but both isolation and assessment of significance may be difficult if the specimen is one, such as sputum, which is liable to be contaminated heavily when upper respiratory tract secretions and commensal bacteria. Scanty Pneumococci are detected, it cannot be assumed that they have a pathogenic role, for they may have entered ad contaminated the specimen from a site of harmless carriage in the nasopharynx.

D- Intraperitonial injection of sputum into the mice: 

   Animal die in 18-48hours. Blood taken from this mouse heart will give pure culture of Pneumococci. It is very sensitive method, but it is done only experimentally, because of difficulty in maintaining a mouse colony.