Restricted sequence variation in Streptococcus pyogenes penicillin binding proteins

Abstract

A recent clinical report has linked Streptococcus pyogenes {beta}-lactam antibiotic resistance to mutations in the Penicillin Binding Protein PBP2x. To determine whether this is an isolated case or reflects a broader prevalence of mutations that might confer reduced {beta}-lactam susceptibility, we investigated the relative frequency of penicillin binding protein (PBP) sequence variation within a global database of 9,667 S. pyogenes isolates. We found that mutations in S. pyogenes PBPs (PBP2x, PBP1a, PBP1b and PBP2a) occur infrequently across this global database with less than 3 amino acid changes differing between >99% of the global population. Only 4 of the 9,667 strains contained mutations near transpeptidase active sites. The reported PBP2x T553K substitution was not identified. These findings are in contrast to those of 2,520 S. pneumococcus sequences where PBP mutations are relatively frequent and are often located in key {beta}-lactam binding pockets. These data, combined with the general lack of penicillin resistance reported in S. pyogenes worldwide, suggests that extensive, unknown, constraints restrict S. pyogenes PBP sequence plasticity. These findings imply that while heavy antibiotic pressure may select for mutations in the PBPs, there is currently no evidence of such mutations becoming fixed in the S. pyogenes population nor that mutations are being sequentially acquired in the PBPs. ImportancePenicillin is the first line therapeutic option for Streptococcus pyogenes infections. Despite the global high prevalence of S. pyogenes infections and widespread use of penicillin, reports of resistance to penicillin have been incredibly rare. Recently, penicillin resistance was detected in two clinical S. pyogenes isolates with accompanying mutations in the active site of the penicillin binding protein PBP2x, raising concerns that penicillin resistance may become more widespread. We screened a global database of S. pyogenes genome sequences to investigate the frequency of penicillin binding protein (PBP) mutations, identifying that PBP mutations are uncommon relative to Streptococcus pneumoniae. These findings support clinical observations that penicillin resistance is rare in S. pyogenes, and suggest that there are considerable constraints on S. pyogenes PBP sequence variation.