Restricted Sequence Variation in Streptococcus pyogenes Penicillin Binding Proteins

Abstract

A recent clinical report has linked <i>Streptococcus pyogenes</i> β-lactam antibiotic resistance to mutation in the penicillin binding protein (PBP) PBP2x. To determine whether this is an isolated case or reflects a broader prevalence of mutations that might confer reduced β-lactam susceptibility, we investigated the relative frequency of PBP sequence variation within a global database of 9,667 <i>S. pyogenes</i> isolates. We found that mutations in <i>S. pyogenes</i> PBPs (PBP2x, PBP1a, PBP1b, and PBP2a) occur infrequently across this global database, with fewer 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 of PBP2x or PBP1a. The reported PBP2x T553K substitution was not identified. These findings are in contrast to those of 2,520 <i>S. pneumococcus</i> sequences where PBP mutations are relatively frequent and are often located in key β-lactam binding pockets. These data, combined with the general lack of penicillin resistance reported in <i>S. pyogenes</i> worldwide, suggests that extensive, unknown constraints restrict <i>S. pyogenes</i> PBP sequence plasticity. Our 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 <i>S. pyogenes</i> population or that mutations are being sequentially acquired in the PBPs.<b>IMPORTANCE</b> β-Lactam antibiotics are the first-line therapeutic option for <i>Streptococcus pyogenes</i> infections. Despite the global high prevalence of <i>S. pyogenes</i> infections and widespread use of β-lactams worldwide, reports of resistance to β-lactam antibiotics, such as penicillin, have been incredibly rare. Recently, β-lactam resistance, as defined by clinical breakpoints, was detected in two clinical <i>S. pyogenes</i> isolates with accompanying mutations in the active site of the penicillin binding protein PBP2x, raising concerns that β-lactam resistance will become more widespread. We screened a global database of <i>S. pyogenes</i> genome sequences to investigate the frequency of PBP mutations, identifying that PBP mutations are uncommon relative to those of <i>Streptococcus pneumoniae</i> These findings support clinical observations that β-lactam resistance is rare in <i>S. pyogenes</i> and suggest that there are considerable constraints on <i>S. pyogenes</i> PBP sequence variation.