Molecular characterization and antimicrobial resistance of 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 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.