beta-Lactamase-producing Moraxella catarrhalis may prevent the emergence of penicillin-resistant Streptococcus pneumoniae in children with recurrent acute otitis media.

We studied the effect of concomitant nasopharyngeal carriage of beta-lactamase producing Moraxella catarrhalis and Haemophilus influenzae on the occurrence of penicillin resistance of Streptococcus pneumoniae. We took nasopharyngeal samples from 306 children with recurrent otitis media and a history of several antibiotic treatments. We could isolate at least one of the pathogens in 89 subjects. Of these children 13% carried more than one pathogen. Of the isolated M. catarrhalis and H. influenzae strains 93% and 43% produced beta-lactamase, respectively. Of the S. pneumoniae strains 25% were non-susceptible (I/R) to penicillin. However, in patients carrying beta-lactamase-producing M. catarrhalis together with pneumococci all strains were susceptible to penicillin (P=0.0353). This finding suggests that beta-lactamase producing M. catarrhalis may hinder the emergence of penicillin resistance of S. pneumoniae in children with recurrent acute otitis media.