Important Mutations Contributing to High-Level Penicillin Resistance in Taiwan19F-14, Taiwan23F-15, and Spain23F-1 of Streptococcus pneumoniae Isolated from Taiwan.

Penicillin-resistant Streptococcus pneumoniae is a serious concern worldwide. In this study, we analyzed the cause of β-lactam resistance in pandemic multidrug-resistant clones. A total of 41 penicillin-nonsusceptible clinical isolates were collected from 1996 to 2012. Sero- and molecular typing confirmed that these isolates were clonal types of Taiwan19F-14, Taiwan23F-15, and Spain23F-1. Sero-switching was found in four isolates. All isolates were multidrug resistant. Sequencing analysis of the penicillin binding proteins (PBPs) was performed on PBP1a, 2b, and 2x, and a large number of mutations were identified in comparing to clinical penicillin-susceptible isolates and the recipient strain R6 used for homologous recombination. The T451A substitution was the key amino acid in PBP2b that contributed to penicillin resistance. T338A in PBP2x played a role in resistance and reached the highest level of resistance when combined with other mutations in PBP2x. High-level penicillin resistance could not be obtained without the combination of mutations in PBP1a with PBP2b and 2x. The amino acid substitutions in PBP1a, 2b, and 2x were the crucial factors for β-lactam resistance.