Serotype replacement and an increase in non-encapsulated isolates among community-acquired infections of Streptococcus pneumoniae during post-vaccine era in Japan

Shin-Ichi Yokota; Naoyuki Tsukamoto; Toyotaka Sato; Yasuo Ohkoshi; Soh Yamamoto; Noriko Ogasawara

doi:10.1016/j.ijregi.2023.07.002

Serotype replacement and an increase in non-encapsulated isolates among community-acquired infections of Streptococcus pneumoniae during post-vaccine era in Japan

IJID Reg. 2023 Jul 15:8:105-110. doi: 10.1016/j.ijregi.2023.07.002. eCollection 2023 Sep.

Authors

Shin-Ichi Yokota¹, Naoyuki Tsukamoto², Toyotaka Sato^{3

4

5}, Yasuo Ohkoshi^{1

6}, Soh Yamamoto¹, Noriko Ogasawara^{1

7}

Affiliations

¹ Department of Microbiology, Sapporo Medical University School of Medicine, Sapporo, Japan.
² Hokkaido Laboratory, SRL, Inc., Sapporo, Japan.
³ Laboratory of Veterinary Hygiene, Faculty of Veterinary Medicine, Hokkaido University, Sapporo, Japan.
⁴ Graduate School of Infectious Diseases, Hokkaido University, Sapporo, Japan.
⁵ One Health Research Center, Hokkaido University, Sapporo, Japan.
⁶ Department of Clinical Laboratory, NTT Medical Center Sapporo, Sapporo, Japan.
⁷ Department of Otolaryngology-Head and Neck Surgery, Sapporo Medical University School of Medicine, Sapporo, Japan.

Abstract

Objectives: It is feared that the serotype replacement of Streptococcus pneumoniae occurred by the introduction of pneumococcal vaccines as periodical inoculation leads to reduced efficacy of the approved vaccines and altered antimicrobial susceptibility.

Methods: We determined serotypes of 351 S. pneumoniae isolates collected at a commercial clinical laboratory in Hokkaido prefecture, Japan, from December 2018 to February 2019 by using the polymerase chain reaction procedure of the US Centers for Disease Control and Prevention. Antimicrobial susceptibility and resistance gene profiles were also examined.

Results: Vaccine coverage rates were 7.9% for 13-valent conjugate vaccine, and 32.5% for 23-valent polysaccharide vaccine, respectively. Non-typable strains were 19.7%. cpsA-positive isolates (group I), and null capsule clade (NCC)1, NCC2 and NCC3 (group II) comprised 31.3%, 28.4%, 32.8%, and 7.5% of the 69 non-typable strains, respectively. No penicillin-resistant/intermediate isolates were found; however, serotypes 35B and 15A/F showed low susceptibility to β-lactams. Only five strains (1.4%) were levofloxacin-resistant, and all were from the older persons, and three strains were serotype 35B.

Conclusion: The progression of serotype replacement in non-invasive pneumococcal infections has occurred during the post-vaccine era in Japan, and non-encapsulated isolates, such as NCC, have increased. Antimicrobial susceptibility is not worsened.

Keywords: Antimicrobial susceptibility; Capsular serotype; Null capsule clade; Resistant genes; Serotype replacement; Streptococcus pneumoniae.