Haemophilus (G-)

Question 1

what type of bacteria is haemophilus? G+ or G-? What shape? Does it need O2?

Answer 1

small G- coccobacilli

aerobic (some anaerobic)

Question 2

where does haemophilus colonize?

Answer 2

upper respiratory tract of almost everywhere

• non-typeable strains
• H. influenzae probably infects only ~1/2% of healthy children

***NOTE: influenza is caused by a virus, not to be confused with H. influenzae(thought to be up until 1933)

Question 3

what is a hemin (X factor) and NAD+ (V factor) and why are they important?

Answer 3

• H. influenzae requires these factors for growth

* access to these factors requires lysed blood (choc agar) rather than whole-blood (blood agar) for growth

Question 4

do all haemophilus spp require both hemin and NAD+ factors?

Answer 4

no, H.influenzae has both factors while other species require only NAD+ and growth on blood agar

Question 5

how many typeable h. influenzae strains are there and what makes them typeable?

Answer 5

• 7 antigenically distinct capsular polysaccharides (a-f)

- type b (Hib) MOST VIRULENT: bacteremia (bloodstream) and meningitis in children younger than 2

Question 6

are there also untypeable strains?

Answer 6

• yes there are unencapsulated forms of h. influenzae
• frequent cause of resp tract disease in infants, children, adults
  
  • h. parainfluenzae: sometimes cause pneumonia/bact endocarditis
  • h. ducreyl: chancroid (STD)
  • h. aphrophilus: in normal flora of mouth/bacterial endocarditis
  • h. aegyptius: conjunctivitis & brazilian purpuric fever

Question 7

**name the virulence factors of haemophilus sp. diseases

Answer 7

• polyribosyl ribitol phosphate (PRP) capsule
  
  • resistance to phagocytosis (as long as Ab not present)
  • basis for Hib vaccine
• endotoxin, causing pathogen-directed endocytosis
• IgA1 protease: similar to NEISSERIA
• pili and OM proteins: similar to NEISSERIA

Question 8

what is the host defense to haemophilus?

Answer 8

antibodies to capsule are protective

Question 9

in 1985 immunization infants for haemophilus began. for which type? and which type of vaccine produces antibodies?

Answer 9

• pure Hib PRP polysaccharide vaccine is not immunogenic in infants
• PRP-conjugated diptheria toxoid (adjuvant) produces good antibody responses in infants
• *** vaccine is against type B

Question 10

how is haemophilus treated?

Answer 10

• many h. influenzae and non-typeable isolates produce beta-lactamase
  
  • resistant to penicillin or ampicillin
  • chloramphenicol drug of choice
  • 3rd generation cephalosporins (ceftriaxone or cefotaxime): penetrate meninges well and corticosteroids may reduce complications