# Molecular basis of decreased susceptibility to beta-lactam antibiotics in Streptococcus pyogenes > **NIH NIH R21** · METHODIST HOSPITAL RESEARCH INSTITUTE · 2022 · $282,625 ## Abstract DESCRIPTIVE TITLE: Molecular basis of decreased susceptibility to beta-lactam antibiotics in Streptococcus pyogenes PROJECT ABSTRACT/SUMMARY The human bacterial pathogen Streptococcus pyogenes (group A streptococcus, GAS) causes more than 700 million human infections annually worldwide. Beta-lactam antibiotics are, and have been, the first-line treatment for GAS pharyngitis and invasive infections. For reasons that remain shrouded in mystery and speculation, this pathogen has continued to be uniformly susceptible to beta-lactam antibiotics for 70 years. However, a recent paper described two GAS infection-causing strains with significantly decreased susceptibility to the beta-lactam antibiotics ampicillin and amoxicillin, causing great concern in the United States and international infectious disease community. This revelation, coupled with our recent discovery that invasive GAS strains with significantly decreased susceptibility to beta-lactam antibiotics are far more common and geographically widespread than previously thought, have served as the catalyst for the research proposed herein. To achieve our goal of greatly enhancing current understanding of the relationship between specific gene mutations and decreased GAS beta-lactam susceptibility, the following two specific aims are proposed. Specific Aim 1: Sequence and analyze the genomes of >11,000 strains to define the spectrum of mutations present in the penicillin-binding protein 2X (pbp2x) and penicillin-binding protein 1A (pbp1A) genes in GAS recovered from pharyngitis and asymptomatic carriers. We will determine MICs for nine commonly used beta-lactams on 2,750 (25%) of the strains. Mutations in these two genes are known to confer decreased beta-lactam susceptibility in many organisms, including pathogenic streptococci. We will exploit our unique collection of 40,000 GAS strains recovered over decades from global sources. Specific Aim 2: Construct and analyze 50 isogenic mutant strains to test the hypothesis that specific naturally-occurring amino acid replacements in PBP2X and PBP1A decrease the susceptibility of GAS to beta-lactam antibiotics, as judged by MIC susceptibility analysis. The results of the studies proposed in these two aims will provide extensive unique data necessary to more fully understand the scope of this critical new antimicrobial resistance threat. It is reasonable to speculate that the resulting data may also ultimately lead to novel translational strategies to prevent, limit, and treat antibiotic-resistant GAS infections. A key motivation is to generate and make available this extensive molecular data in a very short timeframe so that it can be of the greatest use to the research, medical, and public health communities. We believe much of the proposed research should have been done two decades ago, soon after it was recognized that we had massive gaps in our knowledge about how GAS develops decreased susceptibility to beta-lactam antibiotics. Foremost, the propos... ## Key facts - **NIH application ID:** 10449481 - **Project number:** 1R21AI155842-01A1 - **Recipient organization:** METHODIST HOSPITAL RESEARCH INSTITUTE - **Principal Investigator:** James MALLORY Musser - **Activity code:** R21 (R01, R21, SBIR, etc.) - **Funding institute:** NIH - **Fiscal year:** 2022 - **Award amount:** $282,625 - **Award type:** 1 - **Project period:** 2022-03-24 → 2024-02-29 ## Primary source NIH RePORTER: https://reporter.nih.gov/project-details/10449481 ## Citation > US National Institutes of Health, RePORTER application 10449481, Molecular basis of decreased susceptibility to beta-lactam antibiotics in Streptococcus pyogenes (1R21AI155842-01A1). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10449481. Licensed CC0. --- *[NIH grants dataset](/datasets/nih-grants) · CC0 1.0*