Antimicrobial susceptibility of nasopharyngeal isolates of potential pathogens recovered from infants before antibiotic therapy

Antimicrobial susceptibility was determined for strains of Streptococcus pneumoniae, nontypable Haemophilus influenzae and Moraxella catarrhalis recovered from the nasopharynxes of children followed from birth. The bacteria tested were the first potential pathogens isolated from each child before any treatment with antibiotics. Minimal inhibitory concentrations of commonly used oral antibiotics demonstrated the following overall rates of resistance for (1) S. pneumoniae: penicillin 1.2% (intermediate susceptibility 4.8%), trimethoprim-sulfamethoxazole 20%; (2) nontypable H. influenzae: ampicillin 32%, cefaclor 17%; (3) M. catarrhalis: ampicillin 90%, trimethoprim-sulfamethoxazole 19%. Antibiotic regimens used for treatment of otitis media may have to be evaluated in light of changing antibiotic susceptibilities.