In vitro susceptibility of Haemophilus influenzae to eight antibiotics.

Freshly isolated strains of Haemophilus influenzae type B were studied for their in vitro susceptibility to eight antibiotics with a low concentration inoculum. No organisms were identified as being resistant to ampicillin, but minimal inhibiting concentrations for that antibiotic were somewhat higher than reported previously for a similar method. Carbenicillin and ticarcillin resembled ampicillin in activity, and the three agents were more effective on a weight basis than the other agents tested.