Why won’t H. influenzae grow on sheep blood agar?
(a) Sheep blood cells produce neither X factor nor V factor
(b) Sheep blood cells produce only X factor
(c) Sheep blood cells produce only V factor
(d) Sheep blood cells produce both X and V factors, but an enzyme present in the blood hydrolyzes the V factor
D)
Sheep blood cells produce both X and V factors, but an enzyme present in the blood hydrolyzes the V factor.Haemophilus influenzae requires both X factor (hemin) and V factor (nicotinamide adenine dinucleotide, or NAD) for growth. While sheep blood agar contains both factors, the presence of an enzyme in sheep blood can hydrolyze the V factor, rendering it unavailable for H. influenzae to utilize for growth. Thus, H. influenzae cannot grow on plain sheep blood agar without additional supplementation (e.g., with chocolate agar, which provides the factors in an available form).