Molecular characterization and antimicrobial resistance of Streptococcus pneumoniae isolated from adult patients with invasive pneumococcal disease in northern Japan, 2017-2023

Objectives

This study aimed to elucidate the molecular characteristics and antimicrobial resistance of Streptococcus pneumoniae isolates from adults with invasive pneumococcal disease (IPD) in the northern main island of Japan.

Methods

A total of 45 isolates obtained from adults (aged 41-98 years) with IPD between 2017 and 2023 were analyzed for serotype, sequence type (ST), and antimicrobial susceptibility.

Results

Of the 45 isolates, serotype 3-ST180 (24.4%) was the most prevalent, followed by 23A-ST338/ST5242 (13.3%); 23F-ST242/ST1437/ST3543 (8.9%); and 6D-ST282, 15A-ST63, 35B-ST558, and 34-ST1439/ST7388 (6.7% each), which collectively accounted for 73.4% of all isolates. The proportion of the pneumococcal conjugate vaccine (PCV) 13, PCV20, and 23-valent polysaccharide vaccine (PPSV23) serotypes were 44.5%, 46.7%, and 44.5%, respectively. The rate of non-susceptibility to penicillin was 24.4%, and the majority (n = 10 of 11, 90.9%) were also non-susceptible to erythromycin and tetracycline. The multidrug resistance rate for the non-PCV20/PPSV23 serotype was 83.3%, which was higher than the 71.4% for the vaccine serotypes. Among the non-PCV20/PPSV23 serotypes, 23A, 6D, 15A, 35B, and 6E (genetic variant of 6B) showed multidrug resistance with non-susceptibility to penicillin.

Conclusions

The present study revealed that the non-vaccine serotypes in IPD among adults were associated with a high prevalence of non-susceptibility to antimicrobial agents, suggesting the need for continuous surveillance.