Characterization of an Ampicillin-Resistant Haemophilus influenzae Type B

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Abstract
A 28-year-old female in Denver was found in early 1974 to have frontal sinusitis, osteomyelitis, and bacteremia due to Haemophilus influenzae , type B. The minimal inhibitory concentration of ampicillin for this organism was 100 μg/ml and the minimal bactericidal concentration was >100 μg/ml. It was inhibited by chloramphenicol at 0.4 μg/ml. Further studies demonstrated that ampicillin and methicillin were synergistic against this organism. It was shown to produce a diffusible beta-lactamase. Transferase of resistance from this organism to a susceptible Haemophilus parainfluenzae and a reciprocal transfer were accomplished. A test for transformation was negative as was a test for reversal of resistance by ethylenediaminetetraacetic acid.