Abstract
Streptococcus pneumoniae causes severe infections in immunocompromised children and elderly patients. To examine the effects of pneumococcal vaccines, serotypes and drug susceptibility of S. pneumoniae in respiratory specimens were compared before and after the introduction of vaccines. Analyses included 375 strains collected between 2007 and 2009 (prevaccination) and 150 strains collected between 2016 and 2018 (postvaccination). Because serotypes 19, 14, and 9 being covered by the pneumococcal conjugate vaccine (PCV13), they were seldom found postvaccination. However, regarding the pneumococcal polysaccharide vaccine (PPV23), the serotypes included were similarly observed during pre- and postvaccinations. In contrast, serotypes 35 and 34, and non-type (NT), which were not covered by the vaccines, increased after vaccination. Furthermore, the drug susceptibility rates of PCG, CTX, and CFPM were significantly increased after vaccination. The frequencies of mutations in pbp1a, pbp2x, and pbp2b were comparable between pre- and postvaccinations (approximately 32.4%). This was due to the appearance of penicillin-resistant S. pneumoniae (PRSP) whose serotypes 23, 35, and NT did not decrease. The respiratory strains of S. pneumoniae postvaccination were found to include a higher percentage of NT strains and a higher frequency of PRSPs than those before the vaccine introduction. Since NTs often form atypical colonies, careful examination is necessary. Furthermore, because PRSPs continue to occur at a high rate, it is important to conduct appropriate drug susceptibility testing.
