Human Tear Fluid Reduces Culturability of Contact Lens-Associated Pseudomonas aeruginosa Biofilms but Induces Expression of the Virulence-Associated Type III Secretion System.
The type III secretion system (T3SS) is a significant virulence determinant for Pseudomonas aeruginosa. Using a rodent model, we found that contact lens (CL)-related corneal infections were associated with lens surface biofilms. Here, we studied the impact of human tear fluid on CL-associated biofilm growth and T3SS expression.



P. aeruginosa biofilms were formed on contact lenses for up to 7 days with or without human tear fluid, then exposed to tear fluid for 5 or 24 h. Biofilms were imaged using confocal microscopy. Bacterial culturability was quantified by viable counts, and T3SS gene expression measured by RT-qPCR. Controls included trypticase soy broth, PBS and planktonic bacteria.



With or without tear fluid, biofilms grew to ∼108CFU viable bacteria by 24 h. Exposing biofilms to tear fluid after they had formed without it on lenses reduced bacterial culturability ∼180-fold (P<.001). CL growth increased T3SS gene expression versus planktonic bacteria [5.46 ± 0.24-fold for T3SS transcriptional activitor exsA (P=.02), and 3.76 ± 0.36-fold for T3SS effector toxin exoS (P=.01)]. Tear fluid further enhanced exsA and exoS expression in CL-grown biofilms, but not planktonic bacteria, by 2.09 ± 0.38-fold (P=.04) and 1.89 ± 0.26-fold (P<.001), respectively.



Considering the pivitol role of the T3SS in P. aeruginosa infections, its induction in CL-grown P. aeruginosa biofilms by tear fluid might contribute to the pathogenesis of CL-related P. aeruginosa keratitis.
School of Optometry, University of California, Berkeley, CA, USA.
Yvonne T
YT
Wu
School of Optometry, University of California, Berkeley, CA, USA.
Connie
C
Tam
School of Optometry, University of California, Berkeley, CA, USA.
Lucia S
LS
Zhu
School of Optometry, University of California, Berkeley, CA, USA; College of Pharmacy, Touro University California, Vallejo, CA, USA.
David J
DJ
Evans
School of Optometry, University of California, Berkeley, CA, USA; Graduate Groups in Vision Science, Microbiology, and Infectious Diseases & Immunity, University of California, Berkeley, CA, USA. Electronic address: fleiszig@berkeley.edu.
Suzanne M J
SM
Fleiszig
D018441:Biofilms; D003261:Contact Lenses; D006801:Humans; D011550:Pseudomonas aeruginosa; D000069296:Type III Secretion Systems; D014774:Virulence
D000069296:Type III Secretion Systems
Pseudomonas aeruginosa; biofilms; contact lenses; human tear fluid; type III secretion system
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