Streptococcus pneumoniae/ pneumococcus pneumoniae
Gram positive cocci, this pathogenic causes pneumonia in human.
Morphology
1. Diameter 1micrometer arranged in pairs, flame shaped.
2. Non- motile, Non-sporing
3. They are capsulated and capsule encloses each pair.
Characteristics
Grows at 37 degree Celsius at PH 7.8 (optimum temperature).
In blood agar, after incubation for 18 hours, colonies are usually small 0.5-1 micrometre, done shaped with area of partial greenish (Alpha haemolysis) around them.
Sources and Modes of Transmission
It is found in nasopharynx of many healthy individuals. Infection can be transmitted;
1. Exogenously
By droplet from nose of carrier.
2. Endogenously
Infection occurs by individual own microflora (nasopharynx).
Pathogenicity of Streptococcus pneumoniae
Airborne droplets
I
Aspiration
Reached pleura, alveoli, pericardium cause;
Pneumonia, empyema (collection of pus in pleural cavity), pericarditis, septicemia; Bacteria enter into bloodstream cause blood poisoning.
nasopharyngeal carriage
local spread;
Otitis media, sinusitis
Peritonitis; inflammation of peritoneum
Arthritis; Inflammation of bone
Meningitis; Inflammation of brain and spinal card meninges
Septicemia
Pathogenesis
Bacterial capsule and associated enzyme cause following diseases;
1. Acute bacterial pneumoniae
2. Otitis media
3. Bacteremia/ sepsis
4. Meningitis
Pneumococcus may also cause empyema, pericarditis, otitis media, peritonitis usually as complication of pneumoniae.
Laboratory Diagnosis
Specimen collection
Nasopharyngeal swab
Blood, pus, Sputum, spinal fluid
Transport
Sterile container and aseptic condition kept 37 degree Celsius.
Direct microscopy
Gram stained smear of specimen show gram positive, flame shaped, capsule can seen by using capsule stain.
Gram positive colonies are small 0.5-1 micrometre with alpha- haemolysis flame shaped. India ink preparation to show pneumococcus capsule.
Culture
Specimen is inoculated on blood sugar and incubated 37 degree Celsius for 24; hours in presence of 5-10% CO2.
Colony morphology and staining
Biochemical reaction
Biochemical test insulin fermentation and bile solubility test.
Antibiotic sensitivity test with optochin
Optochin inhibits growth of colonies of pneumococcus pneumoniae in blood agar plate.
Prevention and Treatment
Prevention;
Prevention; Two types of vaccines;
1. Pneumococcal polysaccharide vaccine (PPV)
2. Pneumococcal conjugate vaccine (PCV)
Treatment
Cephalosporin is most effective against resistant strains of Streptococcus pneumoniae.
Antigenic structure
Most important antigen of pneumococcus is capsular polysaccharide.
Streptococcus pneumoniae produces pore- forming toxin pneumolysin.
Bile solubility test
Streptococcus pneumoniae is bile soluble whereas all other alpha- hemolytic streptococci are bile resistant.
Bile solubility test used to differentiate streptococcus pneumoniae (positive soluble) from alpha-hemolytic streptococci (negative -insoluble).
BST is used to determine the ability of an organism to undergo lysis in the presence of bile salts.
The 2% (tube method) and 10% (plate method) bile solubility reagents are recommended.
Streptococcus pneumoniae processed an autolytic enzyme that breaks down the organism's own cell wall, resulting in cell lysis.
The autolytic process is accelerated in the presence of bile salt sodium deoxycholate.
Damge cell membrane lysed by bile, called positive bile solubility test. Clearance of turbidity, cocci will not appear.
For the negative results; suspension remains turbid, appearance of cocci.
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