H.influenzae Flashcards
1) classification
Family: Pasteurellaceae
Genus: Haemophillus
Species: influenzae
- opportunistic organism
- noncapsulated organism is part of the normal respiratory flora
2) morphology
- Gram negative coccobacillus
- small pleomorphic
- encapsulated strain and non encapsulated strain
3) Growth characteristics
- facultative anaerobes
- fastidious
- require accessory growth factors in vitro:
Factor X (hemin)
Factors V (NAD)
4) antigenic structure
> encapsulated H.influenzae contain capsular polysaccharides of six types: a to f:
- capsular antigen of type b is a polyribose phosphate
> pili
somatic antigens (outer membrane proteins)
Lipopolysaccharides (endotoxin):
!!!! Share many structures with those of neisseriae !!!!
5) virulence factors
- No exotoxins
- polysaccharide capsule:
Polyribose phosphate it type b is a major virulence factor - pili (fimbriae)
- Lipopolysaccharide: lipid A (major role in non-encapsulated strains)
- neuraminidase (facilitate formation of biofilm)
- igA protease
6) Disease
- meningitis:
Main cause of meningitis in unvaccinated children - otitis media
- sinusitis
- epiglottitis
- cellulitis
- Bacteremia
- chronic bronchitis
- pneumonia
7) Microbiological diagnosis
Microscopical examination: > gram-stain: Smears from CSF pleomorphic gram negative rods and PMNLs >methylene blue stain: Pleomorphic rods and PMNLs
Culture:
Isovitalex enriched chocolate agar with 10% CO2:
Small opaque colonies
Blood agar plate:
“Satellite phenomenon”- colonies of H.influenzae around staphylococcal colonies
Specific tests:
Growth around factors X and V
Direct antigen detection tests:
Direct latex agglutination tests are useful for immediate diagnosis of meningitis
8) treatment and prevention
Ampicillin, chloramphenicol or ceftriaxone are recommended
ACV
Children vaccinated with purified type b polysaccharide
