HAEMOPHILUS

Question 1

What are the haemophilus sp.?

Answer 1

-small gm - coccobacilli
* aerobic (some anaerobic)
-colonizes upper respiratory tract of most children and adults
* encapsulated strains (Hib)
* non-typeable strains
* attach via type-IV pili and outer membrane proteins
-Note: influenza is caused by a virus, not to be confused with H. influenzae
* thought to be so up until 1933 (co-occuring opportunistic pneumonia)
-H. influenzae requires hemming (X factor) and NAD+ (V factor) for growth
* access to these factors require lysed blood (chocolate agar) rather than whole-blood (blood agar) for growth
-other haemophilus species require only NAD+
* growth on blood agar
-typeable H. influenzae strains
* seven antigenically distinct capsular polysaccharides
~ a,b,c,d,e,e’, f
-non-typeable H. influenzae strains
* unencapsulated

Question 2

What are some diseases caused by haemophilus sp.?

Answer 2

• H. infleunzae type b (Hib) its the most virulent
  
  • bacteremia (bloodstream) and meningitis in children younger than 2 years
• non-typeable strains (NTHI) frequently cause respiratory tract disease in infants, children, and immunocompromised adults
  
  • H. influenzae is a predominant bacterial pathogen of otitis media (middle ear infection)
  • H. parainfluenzae sometimes causes pneumonia or bacterial endocarditis
  • H. ducreyi causes chancroid (a STD)
  • H. aphrophilus member of the normal flora of the mouth and occasionally causes bacterial endocarditis
  • H. aegyptius causes conjunctivitis and Brazilian purpuric fever

Question 3

What are the virulence factors of HAEMOPHILUS?

Answer 3

• polyribosyl ribitol phosphate (PRP) capsule
  
  • resistance to phagocytosis (as long as antibody not present)
  • basis for Hib vaccine (against H. influenzae type B)
• endotoxin, causing pathogen-directed endocytosis
• IgA1 protease
  
  • autotransporter protein, directs their own secretion out of cell
• Pili and OM proteins
  
  • play important role in adherence to mucosal surfaces
  • pili are involved in twitching motility and require for biofilm formation
• biofilm formation
  
  • NTHI form biofilms within human airways
  • more resistant to host defenses, such as macrophages and neutrophils
  • antibiotics are less effective against bacterial biofilms

Question 4

what’s the host defense against HAEMOPHILUS?

Answer 4

• antibodies against capsule are protective
• immunization of infants (1985)
  
  • pure Hib PRP polysaccharide not immunogenic in infants
  • PRP-conjugated diphtheria toxoid (adjuvant) produces good antibody responses in infants
• unencapsulated strains lack capsule polysaccharides and require development of novel surface targets

Question 5

What’s the treatment for HAEMOPHILUS?

Answer 5

-many H. influenzae and non-typeable isolates produce beta-lactamase
* resistant to penicillin or ampicillin
* chloramphenicol drug of choice
* third generation cephalosporins (ceftriaxone or cefotaxime)
~ penetrate meninges well
~ corticosteroids may reduce complications
-treatement or prevention of biofilm formation reduces bacterial resistance to antimicrobials
-vaccine development is currently underway to prevent infections due to encapsulated strains
* antigens include outer membrane proteins and type-IV pili