Haemophilus influenzae

Question 1

What are the phenotypic characteristics of H. influenzae?

Answer 1

Non-motile Gram-negative small bacilli
Fastidious (needs certain nutrients to grow)

Question 2

What is the ecological niche of H. influenzae?

Answer 2

Exclusive to the human upper respiratory tract

Question 3

Does H. influenzae require oxygen?

Answer 3

It is a facultative anaerobe but it can be cultured aerobically for lab diagnostics because under aerobic conditions it needs X and V factors to grow

Question 4

How is H. influenzae transmitted?

Answer 4

By droplets or direct contact

Question 5

What is the main virulence factor of H. influenzae?

Answer 5

A polysaccharide capsule (types a,b,c,d,e,f)

Question 6

What do the 6 capsule types of H. influenzae contain?

Answer 6

A ribose (pentose) sugar structure which is called a polyribosyl ribitol phosphate capsule

Question 7

How does H. influenzae grow and cause infection?

Answer 7

The capsule is antiphagocytic
Release of LOS form dying bacteria which is a very potent endotoxin
Many cytokines are released which causes a cascade of inflammatory events

Question 8

What are the 3 physiological responses to H. influenzae infection?

Answer 8

C’ activated
Macrophages activated, cytokines released
Clotting activated

Question 9

What is non-typeable Hib?

Answer 9

Strains that lack a polysaccharide capsule and thus are not as virulent
Often colonizers the nasopharynx and rarely causes invasive disease

Question 10

Why are 18-24-month-old infants the most susceptible to a Hib infection?

Answer 10

The level of maternally acquired serum antibody to PRP declines from birth and reaches the lowest level around this time
The level of antibody to PRP then gradually rises as a result of exposure to Hib

Question 11

What is the most common cause of meningitis in infants?

Answer 11

H. influenzae serotype b

Question 12

Which serotypes of H. influenzae are rare in children?

Answer 12

a,c,d,e,f

Question 13

What diseases does H. influenzae cause in adults?

Answer 13

Bacteremia
Pneumonia
Acute bacterial meningitis
Septic arthritis

Question 14

What diseases does H. influenzae cause in children?

Answer 14

Bacteremia
Pneumonia
Acute bacterial meningitis
Osteomyelitis
Cellulitis
Epiglottitis
Septic arthritis

Question 15

What is epiglottitis?

Answer 15

An acute respiratory obstruction caused by cellulitis of the supraglottic tissues
Potentially lethal - swelling of the epiglottis causes total airway obstruction

Question 16

What are the symptoms of epiglottitis?

Answer 16

Onset = explosive
Sore throat, fever, dyspnea
Pooling of oral secretions and drooling
Restlessness, anxiety, sitting with neck extended and chin protruding to reduce airway obstruction

Question 17

What are the diagnostics of H. influenzae?

Answer 17

Isolation of the organism from a sterile body site
It does not grow well on sheep agar blood

Question 18

What is X factor?

Answer 18

Heat-stable iron-containing pigments - porphyrins

Question 19

What is V factor?

Answer 19

A heat-labile and a coenzyme
Can be supplied by nicotinamide adenine dinucleotide
Present in RBCs but must be released from the cell to sustain optimal growth which is why blood agar can’t grow H. influenzae

Question 20

Which types of antibodies are used to treat H. influenzae?

Answer 20

Mostly cell wall inhibitors - third-generation cephalosporins