Upper respiratory tract infections. Ecological and therapeutic aspects of beta-lactamase production with special reference to Branhamella catarrhalis.

Available data indicate that the most common beta-lactamase produced by Branhamella catarrhalis is plasmid mediated. The same enzyme occurs in Moraxella nonliquefaciens, a commensal in the upper respiratory tract. The ability to produce the enzyme, which is known as BRO-1, can be transferred by conjugation from M. nonliquefaciens to B. catarrhalis. Since the first beta-lactamase-producing strains of B. catarrhalis appeared in 1977, the frequency of beta-lactamase production has increased rapidly; figures as high as 76% have been reported. The plasmid-mediated beta-lactamase TEM-1 occurs in several species of the genus Haemophilus. While the frequency of beta-lactamase production in H. influenzae is reported to be 10-15%, the incidence is significantly higher in non-pathogenic Haemophilus species. Both phenoxymethyl-penicillin and ampicillin promote the occurrence of beta-lactamase-producing strains, but the selective pressure exerted by ampicillin seems to be more pronounced. It may be possible to reduce the ecological effects of the penicillins by avoiding overdiagnosis of the most common bacterial infections of the respiratory tract, and by shortening the courses of antibiotic treatment.