Growth of Haemophilus influenzae in simulated blood cultures supplemented with hemin and NAD.

The mean generation time of Haemophilus influenzae in simulated blood cultures is 103 to 107 min. With 0.56 to 0.58 doublings per h, even large inocula of 256 cells per ml reach only 2 X 10(6) cells per ml and produce no visible evidence of growth after 24 h of incubation. Hemin and NAD added to simulated blood cultures triple the rate of growth of H. influenzae, so that even small inocula produce visible turbidity after overnight incubation. With a mean generation time of 36 min, a single cell of H. influenzae in simulated blood culture supplemented with hemin and NAD undergoes 30 doublings in 18 h, producing 2(30) (1.07 X 10(9] cells and visible turbidity.