Incidence of antibiotic-resistant Streptococcus pneumoniae and beta-lactamase-positive Haemophilus influenzae in clinical isolates from patients with otitis media

Background, The prevalence of penicillin-resistant Streptococcus pneumoniae and betalactamase-producing Haemophilus influenzae in otitis media infections is increasing; emergence of these pathogens has complicated treatment. Objectives, To evaluate the incidence of penicillin resistance and the in vitro activity of amoxicillin/clavulanate, cefaclor, loracarbef, cefixime, trimethoprim/sulfamethoxazole, azithromycin and clarithromycin in S. pneumoniae isolates, The in vitro activity of azithromycin, clarithromycin and cefaclor was also evaluated in beta-lactamase-positive and -negative isolates of H. influenzae. Methods. Bacterial isolates of S. pneumoniae and H. influenzae were obtained by tympanocentesis and subsequent culture of middle ear effusion from children with acute otitis media enrolled in a multicenter trial, Susceptibility to test agents was assessed by disk diffusion and broth dilution techniques with criteria established by the National Committee for Clinical Laboratory Standards. Results, Nineteen (31%) of the 61 S. pneumoniae isolates were resistant to penicillin, A significantly lower percentage of the S. pneumoniae isolates were resistant to azithromycin (16%) and clarithromycin (11%) than to penicillin, amoxicillin/clavulanate, cefaclor, loracarbef or cefixime (31% in all cases), Azithromycin was also more active than cefaclor and significantly more active than clarithromycin against the 55 H. influenzae isolates. Conclusions, The susceptibility of resistant and nonresistant strains of S. pneumoniae to azithromycin and clarithromycin and of isolates of R. influenzae to azithromycin, coupled with penetration of azithromycin into the middle ear, may provide a significant advantage in the treatment of otitis media.