Establishment and evaluation of national standard strains of Streptococcus pneumoniae

Objective To establish candidates of national standard strains of Streptococcus pneumoniae by screening clinical isolates of S. pneumoniae according to the Technical Requirements for Evaluation of National Standard Strains of Pathogenic Microorganisms (WS/T 812－2022).

Methods The S. pneumoniae candidate strains were identified by colony morphology, Gram staining, biochemical characteristics.The serotypes of strains were clarified through Quellung and latex agglutination, multiplex polymerase chain reaction, and cpsB gene sequencing, the whole-genome sequencing was carried out using the Nanopore sequencing platform.

Results A total of 21 strains with typical characteristics of S. pneumoniae were screened as the candidate strains among more than 700 clinical isolates of S. pneumoniae. All the 21 strains were consistently confirmed as serotypes 3, 4, 6A, 6B, 7F, 8, 9N, 9V, 10A, 11A, 12F, 14, 15B, 17F, 18C, 19A, 19F, 20, 22F, 23F, 33F by methods mentioned above of typing. The results of stability experiments showed that the colony morphology, Gram staining, biochemical characteristics, and serotypes maintained good consistency with those of the original strain after consecutively regenerating for 30 generations. The 21 strains of S. pneumoniae selected in this study met all the requirements of the national standard bacterial candidates.

Conclusion The 21 strains of S. pneumoniae obtained in this study have the typical characteristics of the corresponding bacteria and can be used as candidates for national standard strains in the surveillance of S. pneumoniae -related diseases and vaccine evaluation.