title: Selective chemical inhibition of agr quorum sensing in Staphylococcus aureus promotes host defense with minimal impact on resistance.
abstract: Bacterial signaling systems are prime drug targets for combating the global health threat of antibiotic resistant bacterial infections including those caused by Staphylococcus aureus. S. aureus is the primary cause of acute bacterial skin and soft tissue infections (SSTIs) and the quorum sensing operon agr is causally associated with these. Whether efficacious chemical inhibitors of agr signaling can be developed that promote host defense against SSTIs while sparing the normal microbiota of the skin is unknown. In a high throughput screen, we identified a small molecule inhibitor (SMI), savirin (S. aureus virulence inhibitor) that disrupted agr-mediated quorum sensing in this pathogen but not in the important skin commensal Staphylococcus epidermidis. Mechanistic studies employing electrophoretic mobility shift assays and a novel AgrA activation reporter strain revealed the transcriptional regulator AgrA as the target of inhibition within the pathogen, preventing virulence gene upregulation. Consistent with its minimal impact on exponential phase growth, including skin microbiota members, savirin did not provoke stress responses or membrane dysfunction induced by conventional antibiotics as determined by transcriptional profiling and membrane potential and integrity studies. Importantly, savirin was efficacious in two murine skin infection models, abating tissue injury and selectively promoting clearance of agr+ but not Δagr bacteria when administered at the time of infection or delayed until maximal abscess development. The mechanism of enhanced host defense involved in part enhanced intracellular killing of agr+ but not Δagr in macrophages and by low pH. Notably, resistance or tolerance to savirin inhibition of agr was not observed after multiple passages either in vivo or in vitro where under the same conditions resistance to growth inhibition was induced after passage with conventional antibiotics. Therefore, chemical inhibitors can selectively target AgrA in S. aureus to promote host defense while sparing agr signaling in S. epidermidis and limiting resistance development.
authors.affiliation: Research Service, New Mexico Veterans Affairs Medical Center, Albuquerque, New Mexico, United States of America; Division of Infectious Diseases, Department of Internal Medicine, University of New Mexico School of Medicine, Albuquerque, New Mexico, United States of America.
authors.forename: Erin K
authors.initials: EK
authors.lastname: Sully
authors.affiliation: Laboratory of Human Bacterial Pathogenesis, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana, United States of America.
authors.forename: Natalia
authors.initials: N
authors.lastname: Malachowa
authors.affiliation: College of Pharmacy, University of New Mexico, Albuquerque, New Mexico, United States of America.
authors.forename: Bradley O
authors.initials: BO
authors.lastname: Elmore
authors.affiliation: Research Service, New Mexico Veterans Affairs Medical Center, Albuquerque, New Mexico, United States of America.
authors.forename: Susan M
authors.initials: SM
authors.lastname: Alexander
authors.affiliation: Department of Emergency Medicine, University of New Mexico, Albuquerque, New Mexico, United States of America.
authors.forename: Jon K
authors.initials: JK
authors.lastname: Femling
authors.affiliation: Research Service, New Mexico Veterans Affairs Medical Center, Albuquerque, New Mexico, United States of America; College of Pharmacy, University of New Mexico, Albuquerque, New Mexico, United States of America.
authors.forename: Brian M
authors.initials: BM
authors.lastname: Gray
authors.affiliation: Laboratory of Human Bacterial Pathogenesis, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana, United States of America.
authors.forename: Frank R
authors.initials: FR
authors.lastname: DeLeo
authors.affiliation: Laboratory of Human Bacterial Pathogenesis, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, United States of America.
authors.forename: Michael
authors.initials: M
authors.lastname: Otto
authors.affiliation: Department of Microbiology, Dartmouth Medical School, Hanover, New Hampshire, United States of America.
authors.forename: Ambrose L
authors.initials: AL
authors.lastname: Cheung
authors.affiliation: Center for Molecular Discovery and Department of Pathology, University of New Mexico School of Medicine, Albuquerque, New Mexico, United States of America.
authors.forename: Bruce S
authors.initials: BS
authors.lastname: Edwards
authors.affiliation: Center for Molecular Discovery and Department of Pathology, University of New Mexico School of Medicine, Albuquerque, New Mexico, United States of America.
authors.forename: Larry A
authors.initials: LA
authors.lastname: Sklar
authors.affiliation: Department of Microbiology, Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America.
authors.forename: Alexander R
authors.initials: AR
authors.lastname: Horswill
authors.affiliation: College of Pharmacy, University of New Mexico, Albuquerque, New Mexico, United States of America.
authors.forename: Pamela R
authors.initials: PR
authors.lastname: Hall
authors.affiliation: Research Service, New Mexico Veterans Affairs Medical Center, Albuquerque, New Mexico, United States of America; Division of Infectious Diseases, Department of Internal Medicine, University of New Mexico School of Medicine, Albuquerque, New Mexico, United States of America.
authors.forename: Hattie D
authors.initials: HD
authors.lastname: Gresham
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000009:adverse effects / Q000737:chemistry / Q000494:pharmacology / Q000627:therapeutic use*; D001426:Bacterial Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D002461:Cell Line, Transformed; D055808:Drug Discovery; D017930:Genes, Reporter / Q000187:drug effects; D057166:High-Throughput Screening Assays; D007113:Immunity, Innate / Q000187:drug effects*; D008264:Macrophages / Q000187:drug effects / Q000276:immunology / Q000378:metabolism / Q000382:microbiology; D008297:Male; D008812:Mice, Hairless; D018345:Mice, Knockout; D008968:Molecular Conformation; D062105:Molecular Docking Simulation; D058990:Molecular Targeted Therapy / Q000009:adverse effects; D009154:Mutation; D010587:Phagocytosis / Q000187:drug effects; D011401:Promoter Regions, Genetic / Q000187:drug effects; D052999:Quinazolinones / Q000009:adverse effects / Q000737:chemistry / Q000494:pharmacology / Q000627:therapeutic use*; D053038:Quorum Sensing / Q000187:drug effects*; D012867:Skin / Q000187:drug effects / Q000382:microbiology; D013207:Staphylococcal Skin Infections / Q000188:drug therapy* / Q000276:immunology / Q000382:microbiology; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000254:growth & development / Q000276:immunology / Q000502:physiology; D013212:Staphylococcus epidermidis / Q000187:drug effects / Q000254:growth & development / Q000276:immunology / Q000502:physiology; D015534:Trans-Activators / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D014230:Triazoles / Q000009:adverse effects / Q000737:chemistry / Q000494:pharmacology / Q000627:therapeutic use*
chemical_list: C095698:Agr protein, Staphylococcus aureus; D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D052999:Quinazolinones; D015534:Trans-Activators; D014230:Triazoles; C000600149:savirin