beta-Lactamase activity in sputum and indirect pathogenicity.

beta-Lactamase activity of sputum of 39 patients with respiratory infections and that of bacterial isolates from their sputum were determined by nitrocefin method. Forty-six microbial strains (16 different species) were recovered from 39 sputum samples. The beta-lactamase activity was negative only in nine of the 46 strains. beta-lactamase-positive strains were recovered from 35 of 39 sputum samples. Of these 35 sputum samples, the beta-lactamase activity was positive in 23 and negative in 12. beta-lactamase-negative strains were recovered from 4 of 39 sputum samples, and the beta-lactamase activity was negative in all of these four sputum samples. Both beta-lactamase producing and non-producing strains were recovered in 5 of 6 sputum samples from which two to three microbes were isolated. The ratio of beta-lactamase-positive sputum sample was higher in patients who had received antibiotics than in those who had received no antibiotics. This difference was statistically significant (P < 0.025). It is possible that non-causative beta-lactamase-positive organisms enhance the pathogenicity of causative organisms that are beta-lactamase-negative.