S. pneumoniae -Morphology, culture, antigens

• Gram positive, lanceolate shaped diplococcus - 
• Pneumococci 
•  Formerly called, Diplococcus pneumoniae 
•  Normal inhabitants of the human upper respiratory tract 
• Common cause of Pneumonia and Otitis media in children 
•  Also cause Sinusitis, Bronchitis, Bacteremia, Meningitis 
• First noticed by Louis Pasteur and Sternberg- inoculated with human saliva in rabbits and produced fatal septicemia- isolated pneumococci from the blood of infected rabbits- 
• Fraenkel and Weichselbaum established the relation between pneumonia and pneumococci

MORPHOLOGY 

-Small, slightly elongated cocci 

- One end broad or rounded and the other pointed 

- Flame shamed or lanceolate Occur in pairs with broad ends in apposition 

-Capsulated- a pair in a capsule- capsule best seen in material taken from exudates and maybe lost on repeated subcultures 

-Seen as more rounded in culture- Typical morphology may not occur 

- Non motile 

-Non spore forming 

-Gram positive-readily stained with aniline dyes

- Capsule demonstrated in India ink preparation 

CULTURAL CHARACTERISTICS 

 Complex growth requirements-Enriched media 

- Aerobes and facultative anaerobes 

- On Blood agar, at 18 hours, colonies are small (0.5 – 1 mm), dome shaped and glistening with α haemolysis (green discolouration)

- Further incubation, colonies become flat with raised edges and central umbonation -Concentric rings on surface when viewed from above - Draughtsman or carrom coin appearance 

- Large Mucoid clonies ( types 3 and 7)- abundant capsular material 

-Under anaerobic conditions, ß haemolysis in due to oxygen labile Hemolysin O

-Glucose broth – growth occurs as uniform turbidity 

- Readily undergoes autolysis due to the activity of intracellular enzymes 

-Autolysis is enhanced by bile salts, Sodium lauryl sulphate and surface active agents 

ANTIGENIC PROPERTIES

Important antigens

• ·         Capsule
• ·         Nucleoprotein antigen
• ·         ‘C’ carbohydrate antigen u C – reactive protein (CRP)

Type specific Capsular polysaccharide –diffuses into culture medium/exudates/tissues- Specific Soluble Substance (SSS)

Based on Antigenic nature of Capsular polysaccharide, pneumococci were classified into pneumonia causing  I, II, III and heterogenous IV group

IV group has 90 serotypes named 1, 2, 3 and so on

Serotyping carried out by agglutination of cocci with type specific antiserum, Precipitation of SSS with specific serum or capsule swelling reaction/Quellung reaction  demonstrated by Neufeld

Quellung reaction  (Neufeld in 1902)

Suspension of S. pneumoniae is mixed on a slide with a drop of type specific antiserum and a loopful of methylene blue - Capsule becomes swollen and refractile (scatter light)

Done directly with sputum in acute pneumonia cases- was done routinely in the past when the specific antiserum was used for treatment of pneumonia

CRP –Abnormal protein (beta globulin) which precipitates with the somatic C antigen of pneumococci-appears in acute phase of pneumonia, disappear later.

C reactive protein- common in other pathological conditions too.

Not an antibody produced in pneumococcal infections- produced in hepatocytes- stimulated by bacterial infections, inflammation, tissue destruction

Smooth to rough (S – R) variation

In the R form, cocci are non capsulated, auto agglutinable and avirulent –arise as spontaneous mutants in cultures and outgrow S forms, In tissues R mutants are eliminated by phagocytosis

Rough S. pneumoniae of one serotype may be made to produce capsules of the same or different serotype, on treatment with DNA from the respective serotypes

Transformation by Griffith (1928)- demonstration of genetic material in bacteria