S.pneumoniae Flashcards
1) classification
Family: streptococcaceae
Genus: steptococcus
Species: s.peumoniae
S.pneumoniae is a separate microorganism; doesn’t belong to any Lancefield classification
Transported via air droplet
Humans are normal respiratory mucosa carriers
Factors such as alcohol, drug intoxication, viral or other infection can lower natural immunity
2) morphology
- gram positive
- lancet shaped diplococcus
- capsulated
The capsule enclose each pair
3) growth characteristics
- facultative anaerobes
- fastidious
- 35 to 37 oC
- grows best in 5% CO2
- ferment carbohydrate
- catalase negative
4) antigenic structure
- capsular polysaccharide
- somatic antigen
C polysaccharide
Binds with C reactive protein to activate complement- mediated phagocytosisF antigen
M protein - cell wall components:
Teichnoic acid
Peptidoglycan
5) virulence factors
- capsular polysaccharide
- choline binding protein A/ pneumococcal surface protein AThese are adhesins
- enzymes:
Neuramidase
IgA proteases - toxins:
Pneumolysin O
Autolysin - hydrogen peroxide
- pili
6) disease
- pneumonia
- bacteremia
- meningitis
- infections of the upper respiratory tract: otitis, sinusitis
Most common hospital acquired pneumococcal
7) microbiological diagnosis
> culture
Blood agar plate: Small round colonies - first dome-shaped - later a central umbonation Alpha hemolysis
> specific tests
Catalase- negative
Optochin- sensitive (S)
Bile- soluble
> direct antigen detection tests
Direct latex agglutination tests are useful in the immediate diagnosis of meningitis
8) treatment and prevention
- penicillin G is the drug of choice
15% show resistance to penicillin G due to alteration in PBP - In such case, third generation cephalosporin is used
Vancomycin is to be reserved for life threatening illness with highly resistant strains
> antimicrobial susceptibility tests:
Disk diffusion susceptibility testing should be done routinely on isolated from significant infections
