title: Pseudomonas aeruginosa Survival at Posterior Contact Lens Surfaces after Daily Wear.
abstract: OBJECTIVE
  Pseudomonas aeruginosa keratitis is a sight-threatening complication of contact lens wear, yet mechanisms by which lenses predispose to infection remain unclear. Here, we tested the hypothesis that tear fluid at the posterior contact lens surface can lose antimicrobial activity over time during lens wear.
  
  
  METHODS
  Daily disposable lenses were worn for 1, 2, 4, 6, or 8 hours immediately after removal from their packaging or after presoaking in sterile saline for 2 days to remove packaging solution. Unworn lenses were also tested, some coated in tears "aged" in vitro for 1 or 8 hours. Lenses were placed anterior surface down into tryptic soy agar cradles containing gentamicin (100 μg/mL) to kill bacteria already on the lens and posterior surfaces inoculated with gentamicin-resistant P. aeruginosa for 3 hours. Surviving bacteria were enumerated by viable counts of lens homogenates.
  
  
  RESULTS
  Posterior surfaces of lenses worn by patients for 8 hours supported more P. aeruginosa growth than lenses worn for only 1 hour, if lenses were presoaked before wear (∼ 2.4-fold, p = 0.01). This increase was offset if lenses were not presoaked to remove packaging solution (p = 0.04 at 2 and 4 hours). Irrespective of presoaking, lenses worn for 8 hours showed more growth on their posterior surface than unworn lenses coated with tear fluid that was aged for 8 hours in vitro (∼ 8.6-fold, presoaked, p = 0.003; ∼ 5.4-fold from packaging solution, p = 0.004). Indeed, in vitro incubation did not impact tear antimicrobial activity.
  
  
  CONCLUSIONS
  This study shows that postlens tear fluid can lose antimicrobial activity over time during contact lens wear, supporting the idea that efficient tear exchange under a lens is critical for homeostasis. Additional studies are needed to determine applicability to other lens types, wearing modalities, and relevance to contact lens-related infections.
authors.affiliation: *BOptom, PhD, FAAO †BA ‡PhD §OD, PhD, FAAO School of Optometry, University of California, Berkeley, Berkeley, California (all authors); College of Pharmacy, Touro University California, Vallejo, California (DJE); and Graduate Groups in Vision Science, Microbiology, and Infectious Diseases and Immunity, University of California, Berkeley, Berkeley, California (SMJF).
authors.forename: Yvonne T
authors.initials: YT
authors.lastname: Wu
authors.forename: Lucia S
authors.initials: LS
authors.lastname: Zhu
authors.forename: K P Connie
authors.initials: KP
authors.lastname: Tam
authors.forename: David J
authors.initials: DJ
authors.lastname: Evans
authors.forename: Suzanne M J
authors.initials: SM
authors.lastname: Fleiszig
mesh_terms: D000328:Adult; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001422:Bacterial Adhesion / Q000502:physiology*; D015169:Colony Count, Microbial; D003263:Contact Lenses, Hydrophilic / Q000382:microbiology*; D004209:Disposable Equipment; D024881:Drug Resistance, Bacterial / Q000502:physiology; D005260:Female; D005839:Gentamicins / Q000494:pharmacology; D006801:Humans; D008297:Male; D011550:Pseudomonas aeruginosa / Q000302:isolation & purification / Q000502:physiology*; D013666:Tears / Q000502:physiology*; D013997:Time Factors; D055815:Young Adult
chemical_list: D000900:Anti-Bacterial Agents; D005839:Gentamicins