Development of beta-lactamase-mediated resistance to penicillin in middle-ear isolates of Moraxella catarrhalis in Finnish children, 1978-1993.

The frequency of beta-lactamase production was analyzed in a study of 1,452 strains of Moraxella catarrhalis and 2,738 strains of Haemophilus influenzae isolated from middle-ear fluid of children < 6 years of age at Tampere University Hospital in Tampere, Finland, between 1978 and 1993. In addition, 401 isolates of M. catarrhalis from similar samples collected in different parts of Finland in 1988-1990 were tested for beta-lactamase production; minimal inhibitory concentrations of ampicillin, cefaclor, cephalothin, erythromycin, tetracycline, and trimethoprim-sulfamethoxazole for these strains were determined. These data were compared with figures for the annual consumption of beta-lactam antimicrobials in the community in 1978-1993. A bimodal increase in the proportion of strains of M. catarrhalis producing beta-lactamase was detected: from 0 to 60% in 1978-1983 and from 60% to 80% in 1988-1990. Concurrently with the second increase, the consumption of cephalosporins increased substantially in the community. The frequency of beta-lactamase-producing strains of H. influenzae did not increase between 1978 and 1993.