Isoelectric focusing of beta-lactamases from sputum and middle ear isolates of Branhamella catarrhalis recovered in the United States.

Branhamella catarrhalis obtained from the sputum of 146 patients with lower respiratory tract disease and from middle ear fluids of 26 children with otitis media were evaluated for beta-lactamase activity and the enzymes were characterised by isoelectric focusing (IEF). 71% (103 of 146) of the sputum isolates and 77% (20 of 26) of the ear isolates produced beta-lactamase. By IEF, the beta-lactamases of 113 of 123 (92%) strains revealed patterns identical with the Ravasio type strain, having unique enzyme bands at pIs of 6.4 and 6.65. The remaining 10 isolates (8%) produced patterns similar to the 1908 type strain with a unique band of activity having a pI of 6.55. In addition, the 1908 types revealed a band of minor enzyme activity with a pI of 7.55 that was absent from the Ravasio types. All strains tested shared major enzyme bands with pIs of 5.1, 5.3, 5.55 and 6.1. These results indicate that the most common beta-lactamase(s) produced by clinical isolates of B. catarrhalis in the United States are similar to those produced by the Belgian Ravasio type strain.