Antibacterial activity of nine oral antibiotics against Streptococcus pneumoniae, Haemophilus influenzae and Branhamella catarrhalis.

The efficacy of nine oral antibiotics were analyzed by the agar dilution method against clinical isolates consisting of 87 beta-lactamase positive and negative Haemophilus influenzae and Branhamella catarrhalis strains and 30 Streptococcus pneumoniae strains. The following drugs were tested: cefaclor, cefalexin, cefadroxil, cefradin, phenoxymethylpenicillin, ampicillin, amoxycillin, erythromycin and doxycycline. Inoculations of 10(4) bacteria/plate were made with a Steers inoculator on Mueller-Hinton agar containing 5% blood. Cefaclor was more effective than the other cefalosporins against all H. influenzae and B. catarrhalis strains, regardless of their beta-lactamase production. Cefaclor and cefradin were more effective than cefalexin and cefadroxil against S. pneumoniae strains. Cefaclor was less effective than erythromycin against pneumococci, B. catarrhalis and beta-lactamase positive H. influenzae strains and equally effective against beta-lactamase negative H. influenzae strains. Cefaclor was less active than doxycycline against the B. catarrhalis and H. influenzae strains and showed similar efficacy as doxycycline against pneumococci.