Research Project
10108065
PROJECT SUMMARY Group A Streptococcus (GAS) is a strict human pathogen that primarily infects the epithelia at the throat or skin, leading to ~750 million infections per year. High rates of morbidity and mortality result from invasive GAS (iGAS) disease. Despite its importance as a global pathogen, there is no vaccine available for GAS. In the C.D.C.'s Antibiotic Resistance Threats Report of 2019, erythromycin-resistant GAS are listed as a ?concerning threat? and the % of invasive GAS (iGAS) isolates resistant to erythromycin has recently tripled. Macrolides are commonly prescribed for patients with ?-lactam allergies, and lincosamides are highly effective against iGAS disease because exotoxin production is halted. The problem of antibiotic-resistance in GAS is further compounded by 2019-2020 reports on the emergence of stable ?-lactam resistance due to altered penicillin- binding proteins; the potential for lateral spread of resistance genes to other GAS strains is very high. The proposed study seeks a deeper understanding of the biological causes and clinical consequences of the acquisition by GAS of mobile genetic elements (MGEs) harboring macrolide-resistance genes (R-genes). Aim 1 seeks to define the genetic architecture of the (near) complete repertoire of MGEs that harbor macrolide- resistance genes in GAS. Aim 2 uses experimental models of horizontal transfer of R-gene-MGEs between GAS strains, to optimize microenvironmental conditions and to generate isogenic pairs of parental-recipient and new recombinant strains. Aim 3 evaluates the effect of MGE acquisition on host cell phenotypes that are independent of drug-resistance; several cargo genes are predicted to alter global gene expression and/or contribute to virulence. Transcriptomes and fitness will be compared for the isogenic pairs. A mouse model for iGAS disease will test the hypothesis that MGE acquisition leads to an increase in the intrinsic virulence of the new recombinant. If correct, data may explain the epidemiological findings on the high association of macrolide-resistance with iGAS disease and thereby, provide a platform for future studies that probe molecular mechanisms. Tools to be developed from the proposed work include a consolidated structural organization for the macrolide- resistance MGEs, to be posted on the interactive user-friendly www.pubmlst.org website (Aim 1), and improved experimental protocols for horizontal gene transfer by filter-mating (Aim 2). In addition to testing the hypothesis that MGEs impart phenotypic changes in an antibiotic-free environment, transcriptome analysis (Aim 3) is exploratory and may provide a window into critical molecular mechanisms.
