Pneumococci
Pneumococci are gram-positive, lancet-shaped diplococci. They are obligate parasites and are facultative anaerobes. They may exist as capsulated or uncapsulated forms. Only the capsulated form is pathogenic. The capsule consists of large polysachharide polymers. 84 serological types of pneumococci have been recognized, distinguished by their capsular polysaccharides (Lund nomenclature). The capsule plays a key role in the pathogenicity of pneumococci; only capsulated strains are pathogenic for man.
Pneumococci is the causative agent of pneumococcal pneumonia. It is often multilobar in nature. Pneumococcal pneumonia develops most often during the course of viral infections of the upper respiratory tract. Complications of pneumococcal pneumonia include empyema, pleurisy, and pericarditis. Pneumococcus is also comonly found in excerbations of COAD. Pneumococcal pneumonia develops most often during the course of viral infections of the upper respiratory tract. Pneumococcal pneumonia is often multilobar. Primary pneumococcal diseases of the upper respiratory tract include sinusitis and otitis media. Progressive infections of the mastoid or paranasal sinuses sometimes extend directly into the subarachnoid space to cause pneumococcal menigitis.
A tentative diagnosis of pneumococcal pneumonia may be made rapidly by examining the patient’s sputum by gram-stain. The bacterium is readily cultured on blood agar plates. Because many healthy humans carry pneumococci in their throats, the demonstration of the organism in sputum or pharyngeal culture does not provide conclusive evidence of pneumococcal infection. Recovery of pneumococci from the patient’s blood, on the other hand is diagnostic. Therefore, blood should be obtained before the commencement of antibiotic therapy . Other bodily fluids should be cultured in the same way and also on blood agar. Pneumococci are morphologically similar to other streptococci of the viridans group but they differ in being bile-soluble and sensitive to optochin.
In the past, patients used to be treated with type-specific antiserum but these are no longer used. Benzylpenicillin is the drug of choice although resistance to this agent is found occasionally, being due to mutations in its penicillin-binding proteins. Erthromycin or clindamycin may be used to treat pneumonia in patients with known hypersensitivity to penicillin.
A pneucoccal vaccine consisting of 23 capsular Ags is now available, and its administration to individuals at high risk of serious/fatal infections is recommended. Such individuals include the elderly and individuals with debilitating diseases.