Beta-lactamase activity in ampicillin-resistant Haemophilus influenzae.

The specific activity, substrate profile, response to inhibitors, inducibility, and cellular localization of the beta-lactamase produced by an ampicillin-resistant strain of Haemophilus influenzae type B were investigated. In these properties the enzyme resembles beta-lactamases produced by other gram-negative bacilli more closely than those produced by gram-positive organisms. It is quite similar to an enzyme found in strains of Klebsiella pneumoniae, and differs significantly from those described in other gram-negative bacilli. Comparison of the substrate profile with the minimal inhibitory concentrations of various beta-lactamase antibiotics suggests that the beta-lactamase plays an important role in the antibiotic resistance of this organism.