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Original Investigation |

Association of Biofilm Formation, Psl Exopolysaccharide Expression, and Clinical Outcomes in Pseudomonas aeruginosa Keratitis Analysis of Isolates in the Steroids for Corneal Ulcers Trial

Michael E. Zegans, MD1; Antonio DiGiandomenico, PhD2; Kathryn Ray, MA3; Amanda Naimie, BS1; Ashley E. Keller, BS2; C. Kendall Stover, PhD2; Prajna Lalitha, MD4; Muthiah Srinivasan, MD4; Nisha R. Acharya, MD, MS3; Thomas M. Lietman, MD3
[+] Author Affiliations
1Deparments of Surgery (Ophthalmology) and Microbiology and Immunology, Geisel School of Medicine at Dartmouth, Hanover, New Hampshire
2MedImmune LLC, Gaithersburg, Maryland
3F. I. Proctor Foundation and Department of Ophthalmology, University of California, San Francisco
4Aravind Eye Hospital, Tamil Nadu, India
JAMA Ophthalmol. 2016;134(4):383-389. doi:10.1001/jamaophthalmol.2015.5956.
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Importance  Bacterial virulence factors are increasingly recognized as important in the understanding of clinical infections.

Objective  To determine whether 2 potential virulence factors, in vitro biofilm formation and Psl exopolysaccharide (EPS) expression, influence clinical presentation or outcomes in Pseudomonas aeruginosa keratitis.

Design, Setting, and Participants  Laboratory investigation using P aeruginosa clinical isolates from the double-blind Steroids for Corneal Ulcers Trial (SCUT), which included patients at Aravind Eye Hospital, Proctor Foundation, University of California, San Francisco, and Dartmouth-Hitchcock Medical Center. SCUT was conducted from September 1, 2006, through February 22, 2010. All data used in this study were obtained during this period. Pseudomonas aeruginosa clinical isolates from SCUT were evaluated for in vitro biofilm formation, and Psl EPS expression was assessed using an anti-Psl monoclonal antibody (mAb) enzyme-linked immunosorbent assay. Planktonic growth kinetics and the susceptibility to anti-Psl mAb-mediated opsonophagocytic killing (OPK) were also evaluated in a subset of isolates. Linear regression assessed associations between SCUT patients’ visual acuity and their corresponding biofilm formation and Psl EPS expression. Generalized estimating equation regression models were used to assess whether the change in visual acuity among SCUT patients was associated with Psl EPS expression or biofilm formation.

Main Outcomes and Measures  Biofilm formation, Psl production, OPK, and visual acuity.

Results  The P aeruginosa SCUT strains produced a mean (SD) in vitro biofilm score of 1.06 (0.32) (range 0.17-2.12). A 1-unit increase in biofilm was associated with a worse visual acuity of 2 lines measured in SCUT patients at baseline (0.20 logMAR; 95% CI, −0.03 to 0.44; P = .09) and 3 months (0.21 logMAR; 95% CI, 0.003 to 0.44; P = .047). Of 101 confirmed P aeruginosa SCUT isolates, 100 expressed Psl EPSs. In addition, all Psl-positive strains evaluated in the OPK assay were susceptible to anti-Psl mAb-mediated OPK.

Conclusions and Relevance  The ability of P aeruginosa keratitis isolates to form biofilms in vitro was correlated with worse vision at presentation and after 3 months in SCUT. Ninety-nine percent of P aeruginosa keratitis isolates from SCUT produced Psl EPSs, and 100% of these evaluated Psl-positive isolates were susceptible to anti-Psl mAb-mediated OPK. These data indicate that biofilm formation and Psl EPSs may be candidate targets for novel therapeutics against P aeruginosa keratitis.

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Figure 1.
Range of Biofilm Formation and Psl Enzyme-Linked Immunosorbent Assay Seropositivity Among 101 Pseudomonas aeruginosa Isolates From the Steroids for Corneal Ulcers Trial

Error bars indicate SD.

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Figure 2.
Opsonophagocytic Killing (OPK) of 19 Isolates From the Steroids for Corneal Ulcers Trial and Psl Seropositivity of Strains

D1 is a known Psl-positive strain PA715, and D21 is a PA715_psl-pr isogenic mutant of PA715 with a deletion in the psl promoter. mAb indicates monoclonal antibody; NA, not applicable.

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Figure 3.
logMAR Visual Acuity vs Time by Biofilm Formation Dichotomized

The median biofilm formation is 1.03. Each point represents a study visit and the mean visual acuity for patients. Rate of vision gain over time is not statistically different (P = .67).

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