From 2008 to 2020, the Taiwan National Notifiable Disease Surveillance System database demonstrated that the incidence of non-vaccine serotype 23A invasive pneumococcal disease (IPD) approximately doubled. In this study, 276 non-repetitive pneumococcal clinical isolates were collected from two medical centers in Taiwan between 2019 and 2021. Of these 267 pneumococci, 60 were serotype 23A. Among them, 50 (83%) of serotype 23A isolates belonged to the sequence type (ST) 166 variant of the Spain9V-3 clone. Pneumococcal 23A-ST166 isolates were collected to assess their evolutionary relationships using whole-genome sequencing. All 23A-ST166 isolates were resistant to amoxicillin and meropenem, and 96% harbored a novel combination of penicillin-binding proteins (PBPs) (1a:2b:2x):15:11:299, the newly identified PBP2x-299 in Taiwan. Transformation of the pbp1a, pbp2b, and pbp2x alleles into the β-lactam-susceptible R6 strain revealed that PBP2x-299 and PBP2b-11 increased the MIC of ceftriaxone and meropenem by 16-fold, respectively. Prediction analysis of recombination sites in PMEN3 descendants (23A-ST166 in Taiwan, 35B-ST156 in the United States, and 11A-ST838/ST6521 in Europe) showed that adaptive evolution involved repeated, selectively favored convergent recombination in the capsular polysaccharide synthesis region, PBPs, murM, and folP genome sites. In the late 13-valent pneumococcal conjugate vaccine era, PMEN3 continuously displayed an evolutionary capacity for global dissemination and persistence, increasing IPD incidence, leading to an offset in the decrease of pneumococcal conjugate vaccine serotype-related diseases, and contributing to high antibiotic resistance. A clonal shift with a highly β-lactam-resistant non-vaccine serotype 23A, from ST338 to ST166, increased in Taiwan. ST166 is a single-locus variant of the Spain9V-3 clone, which is also called the PMEN3 lineage. All 23A-ST166 isolates, in this study, were resistant to amoxicillin and meropenem, and 96% harbored a novel combination of penicillin-binding proteins (PBPs) (1a:2b:2x):15:11:299. PBP2x-299 and PBP2b-11 contributed to the increasing MIC of ceftriaxone and meropenem, respectively. Prediction analysis of recombination sites in PMEN3 descendants showed that adaptive evolution involved repeated, selectively favored convergent recombination in the capsular polysaccharide synthesis region, PBPs, murM, and folP genome sites. In the late 13-valent pneumococcal conjugate vaccine era, PMEN3 continuously displays the evolutionary capacity for dissemination, leading to an offset in the decrease of pneumococcal conjugate vaccine serotype-related diseases and contributing to high antibiotic resistance.
Keywords: PMEN3 variant; Streptococcus pneumoniae; antibiotic resistant; clonal shift; non-vaccine serotype; β-lactam resistant.