Introduction Streptococcus pneumoniae is one of the most common bacteria causing otorhinolaryngological infections, such as acute otitis media and upper respiratory tract infection. Our group surveyed the drug susceptibility profile of S. pneumoniae isolates from otorhinolaryngology patients. Materials and methods A total of 41,069 S. pneumoniae isolates were detected at Miyagi Medical Association Health Center between May 2001 and December 2012. Specimens were obtained from patients at 40 otorhinolaryngology outpatient clinics in Miyagi Prefecture, Japan. The minimum inhibitory concentrations (MICs) of 8 antimicrobial agents were measured using the broth microdilution method according to Clinical and Laboratory Standards Institute guidelines. Results In children aged 0-2 years old, the MIC50 values of penicillins decreased after 2010 (PCG: 1 μg/ml (2010) to 0.06 μg/ml (2012); ABPC: 1 μg/ml (2010) to 0.25 μg/ml (2012)). The prevalence of penicillin-resistant S. pneumoniae (PRSP) decreased from 35.2% (2010) to 14.6% (2012) in rhinorrhea specimens and from 43.4% (2010) to 14.3% (2012) in otorrhea specimens. Susceptibility to cephems (ceftriaxone and cefditoren) and carbapenems (panipenem) also showed improvement after 2010. For macrolides (clarithromycin) and lincosamides (clindamycin), MIC50 values increased in all age groups during the study period, and a high level of resistance was seen until 2012. There were no marked changes of susceptibility to fluoroquinolones (LVFX) during the study period. Conclusion Improvement of susceptibility of S. pneumoniae to β-lactams occurred after 2010 in Miyagi Prefecture, Japan.
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