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Victoria B. Tran, Suzanne M. Fleiszig, David J. Evans, Clayton J. Radke; Pseudomonas aeruginosa Association To Polyelectrolyte Hydrogel Lenses Is Modulated By pH And Divalent Ions. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6510.
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© ARVO (1962-2015); The Authors (2016-present)
Preventing Pseudomonas aeruginosa (PA) binding to hydrogel soft contact lenses (SCLs) may help reduce the incidence of lens-associated microbial keratitis. Understanding PA binding mechanisms is key to understanding antifouling methods. Previously, we reported that PA associated strongly to hydrogels consisting of methacrylic acid (a common SCL component). We hypothesized that this strong association was due to divalent cationic bridging between PA and the polyelectrolyte membrane, and that this bridging could be modulated by ion concentration and pH.
Hydrogels were synthesized by UV-initiated polymerization of MAA or AA with cross-linker (EGDMA), water, and acetonitrile. Mian’s minimal media containing 5 x106 cfu/ml PA strain PAK, was pumped through a flow chamber containing a mounted membrane for 1-2 h at a constant shear rate (0.2 s-1). Attachment dynamics were visualized and quantified by phase-contrast video microscopy. Hydrogel swelling and shrinking in solutions were visualized using drop shape analysis software.
Hydrogels pretreated in PBS, pH 7.4, showed few bacteria associating: 750 ± 250 bac/mm2. Within 20 min of incorporating Mg or Ca (10 mM or 5 mM, respectively) into the suspension, association rose to 5300 ± 2000 bac/mm2. Increased association did not sustain and dropped to 1500 ± 500 bac/mm2 after 1 h. Adding EDTA and then restoring Mg or Ca caused bacteria association to rise again to 5000 ± 1000 bac/mm2. Pretreating hydrogels in water, pH 6.2, gave less PAK association: 1370 ± 61 bac/mm2 even in presence of divalent ions. Due to carboxylic side group dissociation and self-repulsion of resulting anionic polymer chains, MAA hydrogels initially in water, pH 6.2, swelled 3.4 ± 0.5x their volume when placed in PBS pH 7.4. Upon adding 10-mM MgCl2, MAA hydrogels shrunk 37 ± 5% due to Mg+2 uptake and anionic polymer chain collapse. The apparent reason for enhanced PA uptake of anionic membranes is PA and surface bridging via divalent cations. Polymer chain collapse explains short-lived PA association.
P. aeruginosa strain PAK associated strongly to polyelectrolyte hydrogels in the presence of divalent ions due to divalent cationic bridging. However, this bridging only occurred when the hydrogels’s polymer chains were extended. This study illustrates the sensitive dynamics of PAK binding to hydrogels due to charge interactions which can be modulated by pH, divalent ion concentration, and chelators.
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