The most common cause of ampicillin resistance in Haemophilus influenzae type b is production of TEM-1 beta-lactamase; however, a novel enzyme with a similar substrate profile but a quite different isoelectric point has also been described. This beta-lactamase, designated ROB-1, has not been found previously in any other organism. In a survey of 46 ampicillin-resistant H. influenzae type b isol...