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Natalya Doroshenko, Stephen Rimmer, Simon Foster, Sheila MacNeil, Ian Douglas; Corneal infections: targeted eradication through antibiotic functionalized polymers.. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4293.
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Although corneal infections are routinely treated with topical antimicrobials, dilution of the agent by tear production and the fact that the bacteria are growing as a biofilm community reduces therapeutic efficacy. One approach to improving therapy would be to reduce the microbial burden prior to antimicrobial therapy. We therefore investigated the use of a polymer that selectively binds and removes Staphylococcus aureus as a way of reducing the bioburden in a corneal infection model.
Hyper-branched poly(N-isopropyl acrylamide) functionalised with vancomycin at the chain ends (HB-PNIPAM-Van) was used in this study. It was shown to lack bactericidal activity by conventional assays. Direct binding of S. aureus to immobilised HB-PNIPAM-Van was assessed by viable counting. The effect of HB-PNIPAM-Van on attachment of fluorescently labelled S. aureus to polystyrene microtiter wells was determined by plate reader and microscopy. Also, its effect on 24-h biofilm formation was assessed by crystal violet staining. The ability of the polymer to reduce the bacterial bioburden in a corneal infection model was determined using ex vivo rabbit corneas inoculated with 108 S. aureus. After 24 hours, the corneas were washed and exposed to HB-PNIPAM-Van or PBS as a control for 4 hours and the viable count of S. aureus remaining on the cornea was determined. Two-tailed Student t-test was used for statistical analysis.
The number of S. aureus cells attached to HB-PNIPAM-Van-coated surfaces was significantly greater (p = 0.004) than to polymer-free surfaces, demonstrating the affinity of the polymer for S. aureus. Also HB-PNIPAM-Van significantly inhibited S. aureus biofilm formation (p = 0.0008), which was shown to be due to the polymer interacting with the bacterial cell surface and reducing their ability to attach to the microtiter wells (p = 0.0002). Importantly, addition of HB-PNIPAM-Van to S. aureus infected ex vivo corneas resulted in a decrease of 3.3 x 107 (± 2.4 x 106) CFU per cornea when compared to PBS treatment alone (p = 0.002).
HB-PNIPAM-Van binds S. aureus cells, inhibiting their attachment to surfaces and reducing corneal infection. These findings suggest that HB-PNIPAM-Van may be a useful adjunct to antimicrobial therapy by pre-reducing the bioburden.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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