Penicillin resistance is not extrapolable to amoxicillin resistance in Streptococcus pneumoniae isolated from middle ear fluid in children with acute otitis media

OBJECTIVES: We evaluated the in vitro antibacterial activity of amoxicillin against penicillin-susceptible and -nonsusceptible Streptococcus pneumoniae strains isolated from children with acute otitis media (AOM). METHODS: Children more than 3 months of age with AOM who were seen in the Dr Sótero del Rio and Luis Calvo Mackenna Hospitals in Santiago, Chile, between July 1998 and December 2002 were subjected to tympanic puncture for middle ear fluid culture. The penicillin and amoxicillin susceptibilities of the S pneumoniae isolates were determined by epsilometer test (E test). RESULTS: A bacterial pathogen was isolated in 432 of 543 children (80%) as follows: S pneumoniae, 40%; Haemophilus influenzae, 29%; Moraxella catarrhalis, 7%; and Streptococcus pyogenes, 4%. Penicillin-susceptible S pneumoniae strains were less common than amoxicillin-susceptible strains (60% versus 95%; odds ratio OR], 0.08; 95% confidence interval CI], 0.04 to 0.18). Both intermediate- and high-resistance strains were more common for penicillin (22% versus 4.5%; OR, 5.6; 95% CI, 2.5 to 12.7) than for amoxicillin (18% versus 0.5%; OR, 41.3; 95% CI, 6.0 to 821). CONCLUSIONS: Penicillin resistance is not extrapolable to amoxicillin among S pneumoniae strains isolated from middle ear fluid of children with AOM. Our results support the recommendation to evaluate the minimal inhibitory concentrations of penicillin-nonsusceptible S pneumoniae for amoxicillin and to continue use of this antimicrobial as a first-line antimicrobial choice for children with AOM.