Hemophilus

• What should you be able to describe at the end of the lecture on Haemophilus?


  The morphology, epidemiology, growth conditions, characteristics, pathophysiology, infection types, lab investigation, management, and prevention of Haemophilus infections.
• What type of organisms are Haemophilus?

  They are blood-loving, pleomorphic, small Gram-negative, aerobic organisms.
• Are Haemophilus species strict human pathogens?

  Yes, they are strict human pathogens.

  
• What distinguishes typeable forms of Haemophilus?


  Some species are encapsulated while others are not.

  
• Which type of Haemophilus is considered the most virulent?

  Type b (Hib) is the most virulent.

  
• Where are most species of Haemophilus found in humans?

  Most species, especially the non-typeable forms, are normal flora of the upper respiratory tract (URT).

  
• What is Haemophilus influenzae associated with?

  It is associated with acute upper respiratory tract infections and meningitis mainly in children.

  
• What disease is Haemophilus ducreyi associated with?

  It is associated with chancroid.

  
• What are the other species of Haemophilus mentioned?

  H. parainfluenzae and H. aegypticus.
• What is the Gram stain appearance of Haemophilus?

  They appear as short coccobacilli in chains or singles.

  
• How do young cultures of Haemophilus differ from older ones?

  Young cultures are encapsulated, while older ones have pleomorphic forms.
• What type of media do Haemophilus species grow better in?

  They grow better in enriched media.
• What two growth factors are required for optimal growth of Haemophilus?

  1. x-factor (haematin) and V-factor (NAD or NADP).
• What is the difference between blood agar and chocolate agar for Haemophilus growth?

  Blood agar has only X-factor, while chocolate agar has both X and V factors.
• What is the optimum temperature for Haemophilus growth?

  37°C.
• In what environment do some Haemophilus species grow better?

  Some grow better in a CO2 environment.
• What is the satellite phenomenon in relation to Haemophilus growth?

  S. aureus secretes V factor which supports the growth of Haemophilus in a medium deficient of V factor.

  
• How can the capsular antigen of Haemophilus be demonstrated?

  By agglutination, precipitation, capsular swelling, and immunofluorescence.

  
• Which group of Haemophilus strains causes invasive disease?

  Strains belonging to Group 'b' serotype.

  
• What is the composition of the capsule in Group 'b' strains?

  Polyribitol ribose phosphate (PRP).
• What is the role of the PRP capsule in Haemophilus virulence?

  It prevents opsonization.
• What is the role of endotoxin in Haemophilus virulence?

  It acts as a ciliostatic factor.
• What happens to non-capsulated strains of Haemophilus?

  They are normal flora in the upper respiratory tract.

  
• How has Hib vaccination affected colonization in children?

  It has reduced colonization in children.
• What is the pathogenesis of H. influenzae?

  It displays a remarkable tropism for the epiglottis and can extend to nearby areas like the sinus and ear.

  
• What can lead to disease from non-capsular strains of Haemophilus?

  Disease can occur after damage to the upper respiratory tract, such as from viral infections.

  
• What are some diseases associated with non-capsular strains of Haemophilus?

  Sinusitis, otitis media, and bronchiectasis.

  
• What specimens are used for lab diagnosis of Haemophilus infections?

  Nasopharyngeal swab, pus, blood, and CSF.

  
• What indicates presumptive identification of Haemophilus in sterile sites?

  Small Gram-negative coccobacilli.

  
• What type of agar is used for culturing Haemophilus?

  Chocolate agar and blood agar.
• What is required for the demonstration of the satellite phenomenon in Haemophilus culture?

  37°C in a CO2 environment.
• What test is positive for Haemophilus identification?

  Oxidase test is positive.
• What is the management approach for Haemophilus infections?

  Supportive management.
• What is the treatment for Haemophilus infections?

  Third generation cephalosporin after susceptibility testing.

  
• When is maternal immunity lost in infants?

  Maternal immunity is lost after 3 months.
• Why is there severe disease in children aged 3 months to 3 years?

  Children are unable to produce sufficient antibody against Group 'b' until about 2 years of age.
• How does antibody production change with age?

  Antibody production increases with age, and minor infections improve antibody levels.
• What happens to children after 3 years of age regarding Haemophilus infections?

  They are killed by the anti-bactericidal activity of complement.
• Where is H. ducreyi mostly found?

  In tropical regions.
• What condition is caused by H. ducreyi?

  Chancroid, which is a soft chancre.