Haemophilus influenzae is both X and V factor dependent for growth, and is the most common cause of obstructive laryngitis and epiglottitis. H. parainfluenzae is only V-factor dependent and causes only mild pharyngitis, rarely obstructive in nature. H. aphrophilus can be part of the normal upper respiratory flora in humans, does not cause pharyngitis, and is not X or V-factor dependent for growth. Although H. haemolyticus is both X and V-factor dependent, it is beta hemolytic on blood agar and is generally considered non pathogenic.
Acute obstructive epiglottitis, both in adults and children, is caused by the bacterial species shown in this split screen photograph. The colonies recovered on chocolate agar (upper frame) required both hematin and NAD, (as shown by colony growth only between the X and V strips in the lower frame). The most likely identification is:
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