title: Environmentally Endemic Pseudomonas aeruginosa Strains with Mutations in lasR Are Associated with Increased Disease Severity in Corneal Ulcers.
abstract: The Steroids for Corneal Ulcers Trial (SCUT) was a multicenter, international study of bacterial keratitis in which 101 Pseudomonas aeruginosa infections were treated. Twenty-two of 101 P. aeruginosa isolates collected had a colony morphology characteristic of a loss-of-function mutation in lasR, the gene encoding a quorum-sensing master regulator. Ulcers caused by these 22 strains were associated with larger areas of corneal opacification, worse vision, and a lower rate of vision recovery in response to treatment than ulcers caused by the other isolates. The lasR sequences from these isolates each contained one of three nonsynonymous substitutions, and these strains were deficient in production of LasR-regulated protease and rhamnolipids. Replacement of lasR with either of the two most common lasR alleles from the SCUT isolates was sufficient to decrease protease and rhamnolipid production in PA14. Loss of LasR function is associated with increased production of CupA fimbriae, and the LasR-defective isolates exhibited higher production of CupA fimbriae than LasR-intact isolates. Strains with the same lasR mutation were of the same multilocus sequence type, suggesting that LasR-deficient, environmental P. aeruginosa strains were endemic to the area, and infections caused by these strains were associated with worse patient outcomes in the SCUT study. (This study has been registered at ClinicalTrials.gov under registration no. NCT00324168.) IMPORTANCE The LasR transcription factor is an important regulator of quorum sensing in P. aeruginosa and positively controls multiple virulence-associated pathways. The emergence of strains with lasR loss-of-function alleles in chronic disease is well described and is thought to represent a specific adaptation to the host environment. However, the prevalence and virulence of these strains in acute infections remain unclear. This report describes observations revealing that lasR mutants were common among isolates from a large, multicenter clinical study of keratitis and were associated with worse clinical outcomes than LasR-intact strains despite reduced production of LasR-regulated factors. Additionally, these lasR mutants were closely related strains or clones, as determined by molecular analysis. Because bacterial keratitis is community acquired, these data indicate infection by endemic, LasR-deficient strains in the environment. These results suggest that the conventional paradigm regarding the role for LasR-mediated regulation of virulence is more complex than previously appreciated.
authors.affiliation: Department of Microbiology and Immunology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, USA.
authors.forename: John H
authors.initials: JH
authors.lastname: Hammond
authors.affiliation: Department of Microbiology and Immunology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, USA.
authors.forename: Wesley P
authors.initials: WP
authors.lastname: Hebert
authors.affiliation: Department of Microbiology and Immunology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, USA.
authors.forename: Amanda
authors.initials: A
authors.lastname: Naimie
authors.affiliation: FI Proctor Foundation and Department of Ophthalmology, University of California, San Francisco, San Francisco, California, USA.
authors.forename: Kathryn
authors.initials: K
authors.lastname: Ray
authors.affiliation: Department of Microbiology and Immunology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, USA.
authors.forename: Rachel D
authors.initials: RD
authors.lastname: Van Gelder
authors.affiliation: MedImmune, LLC, Gaithersburg, Maryland, USA.
authors.forename: Antonio
authors.initials: A
authors.lastname: DiGiandomenico
authors.affiliation: Aravind Eye Hospital, Madurai, Tamil Nadu, India.
authors.forename: Prajna
authors.initials: P
authors.lastname: Lalitha
authors.affiliation: Aravind Eye Hospital, Madurai, Tamil Nadu, India.
authors.forename: Muthiah
authors.initials: M
authors.lastname: Srinivasan
authors.affiliation: FI Proctor Foundation and Department of Ophthalmology, University of California, San Francisco, San Francisco, California, USA.
authors.forename: Nisha R
authors.initials: NR
authors.lastname: Acharya
authors.affiliation: FI Proctor Foundation and Department of Ophthalmology, University of California, San Francisco, San Francisco, California, USA.
authors.forename: Thomas
authors.initials: T
authors.lastname: Lietman
authors.affiliation: Department of Microbiology and Immunology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, USA.
authors.forename: Deborah A
authors.initials: DA
authors.lastname: Hogan
authors.affiliation: Department of Surgery (Ophthalmology), Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, USA; Department of Microbiology and Immunology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, USA.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Zegans
keywords: Anr; CupA; LasR; Pseudomonas aeruginosa; SCUT; bacterial keratitis; corneal ulcer; eye infection; quorum sensing