Serotypes and Genotypes of Streptococcus pneumoniae in an Unvaccinated Population in Suzhou, China

Streptococcus pneumoniae is a significant etiological agent of infection and commonly inhabits the human nasopharynx, alongside other potentially pathogenic bacteria. In this study, S. pneumoniae strains were obtained from a community population and subjected to investigation of their phenotypes, genotypes, and vaccine coverage.

S. pneumoniae was isolated from nasopharyngeal swab samples of a healthy population in the Guangfu Community. Capsular serotypes and genotypes were identified using Quellung reaction and multilocus sequence typing (MLST), respectively. The antimicrobial susceptibility was tested using minimum inhibitory concentrations.

In total, 500 unvaccinated people were sampled. Ninety-four S. pneumoniae strains were identified. Common serotypes were 19F, 6A, and 9V. The strain coverages of PCV13 and PPV23 were 61.7% and 58.5%, respectively. About 27.6% isolates were non-susceptible to penicillin, and over 80% were resistant to erythromycin and doxycycline. Among 27 novel sequence types (STs) identified in all strains, the most common STs were ST236 (6/94, 6.4%) and ST12669 (6/94, 6.4%). Nearly half of the strains were grouped into four clone complexes (CC12665, CC271, CC6011, and CC180), of which CC271 showed the highest resistance to PEN.

In our study, various drug-resistant clone complexes of Streptococcus pneumoniae were found in the healthy population, the elderly, and children. Consequently, pneumococcal vaccines should be included in the national immunization schedule to prevent disease spread.