The emergence and spread of nonencapsulated Streptococcus pneumoniae (NESp) is a public health concern in the post-pneumococcal conjugate vaccine era. We analyzed the prevalence, molecular characteristics, and antimicrobial resistance of NESp responsible for non-invasive infections in northern Japan.
Among 4463 S. pneumoniae isolates collected from non-invasive infection cases during four study periods between January 2011 and January 2019, NESp isolates were identified using molecular and phenotypical methods. NESp isolates were analyzed for antimicrobial susceptibility, genotype, and virulence-associated genes.
A total of 71 NESp isolates were identified (1.6% of all the clinical isolates) and assigned to the null capsule clade (NCC)1 (pspK+) (94.4%) or NCC2 (aliC+/aliD+) (5.6%). Five dominant sequence types (STs) were ST7502 (23.9%), ST4845 (19.7%), ST16214 (11.3%), ST11379 (9.9%), and ST7786 (7.0%). These dominant STs and all seven novel STs were related to the sporadic NESp lineage ST1106 or PMEN clone Denmark-ST230. High non-susceptibility rates of NESp were observed for trimethoprim-sulfamethoxazole, erythromycin, and tetracycline (>92.9%), and multidrug resistance was observed in 88.7% of the NESp isolates, including all the ST7502, ST4845, and ST11379 isolates.
The present study revealed that the dominant clonal groups of NESp were associated with a high prevalence of non-susceptibility to antimicrobials in northern Japan.

Copyright © 2021. Published by Elsevier Ltd.