Streptococcus Pneumonia

INTRODUCTION:

• Inhabitants of human upper respiratory tract
• Gram +ve
• Causes pneumonia, otitis media in children, sinusitis, meningitis etc

MORPHOLOGY:

• Lanceolate appearance
• Capsule enclose each pair
• Non motile and Non sporing
• Polysaccharide capsules demonstrated  clear halo in India ink preparations

CULTURAL CHARACTERISTICS:

• Grow on enriched media
• Grow best in 5%carbon dioxide.(fastidios)
• Aerobes and facultative anaerobes
• Optimum temperature 37 ^oC (25-42) and ph of 7.8  (6.5-8.3)
• On blood agar, after 18 hrs  incubation , colonies are dome shaped and glistening 
• An area of green discolouration(alpha hemolysis)

• On further incubation become flat,raised edges and central umbonation
• Draughtsman or carom coin appearance

• Under anaerobic conditions, colonies are surrounded by a zone of beta hemolysin O.
• In liquid media such as glucose broth, growth occurs as uniform turbidity
• The cocci readily undergoes autolysis which is enhanced by bile salts etc

BIOCHEMICAL REACTIONS:

•  Fermentation is tested in Hiss’s serum sugars.
• S. pneumonia are catalase and oxidase negative.
• Fermentation of inulin is a useful test for differentiating them from streptococci, as the latter do not ferment it.

Bile solubility test:

• Few drops of 10% Na deoxycholate soln  added to 1ml  overnight broth culture
• It clears due to lysis of cocci . 
• Bile  solubility is  of diagnostic importance.
• Bile solubility is due to  amidase 
• Amidase cleaves  bond between alanine and muramic acid in the peptidoglycan. 
• The amidase activated by surface active agents like bile or bile salts.

Optochin sensitivity:

TOXINS AND VIRULENCE FACTORS:

The capsular polysaccharide

• Specific soluble substance
• Protect agianst Phagocytosis
• Antibody against it is IgG subclass 2
• Type 3 most virulent due abundant capsular material.

Cell wall Substance:(C substance)

• Unique
• Consist of teichoic acid and choline residue.
• Choline residue provide attachment o Virullence factors PspA and Psa A

Pneumolysin:

•   A membrane damaging toxin has cytotoxic and complement activating properties. Pneumolysin –ve mutants show reduced virulence.

Autolysin

• These helps in releasing bacterial components and toxins like pnemolysin

IgA Protease

• Cleaves human IgA

Quellung reaction:

• Used for rapid identification
• Pneumoocci mixed with specific/polyvalent antipolysaccharide serum
• Capsule becames swollen,sharply delineated and refractile

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