title: Inhibition of bacterial surface colonization by immobilized silver nanoparticles depends critically on the planktonic bacterial concentration.
abstract: Immobilization of antimicrobial silver nanoparticles (AgNPs) on surfaces has been proposed as a method to inhibit biofouling or as a possible route by which incidental releases of AgNPs may interfere with biofilms in the natural environment or in wastewater treatment. This study addresses the ability of planktonic Pseudomonas fluorescens bacteria to colonize surfaces with pre-adsorbed AgNPs. The ability of the AgNP-coated surfaces to inhibit colonization was controlled by the dissolved silver in the system, with a strong dependence on the initial planktonic cell concentration in the suspension, i.e., a strong inoculum effect. This dependence was attributed to a decrease in dissolved silver ion bioavailability and toxicity caused by its binding to cells and/or cell byproducts. Therefore, when the initial cell concentration was high (∼1×10(7)CFU/mL), an excess of silver binding capacity removed most of the free silver and allowed both planktonic growth and surface colonization directly on the AgNP-coated surface. When the initial cell concentration was low (∼1×10(5)CFU/mL), 100% killing of the planktonic cell inoculum occurred and prevented colonization. When an intermediate initial inoculum concentration (∼1×10(6)CFU/mL) was sufficiently large to prevent 100% killing of planktonic cells, even with 99.97% initial killing, the planktonic population recovered and bacteria colonized the AgNP-coated surface. In some conditions, colonization of AgNP-coated surfaces was enhanced relative to silver-free controls, and the bacteria demonstrated a preferential attachment to AgNP-coated, rather than bare, surface regions. The degree to which the bacterial concentration dictates whether or not surface-immobilized AgNPs can inhibit colonization has significant implications both for the design of antimicrobial surfaces and for the potential environmental impacts of AgNPs.
authors.affiliation: Center for Complex Fluids Engineering and Center for Environmental Implications of Nanotechnology, Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, United States.
authors.forename: Stacy M
authors.initials: SM
authors.lastname: Wirth
authors.affiliation: Center for Complex Fluids Engineering and Center for Environmental Implications of Nanotechnology, Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, United States.
authors.forename: Alex J
authors.initials: AJ
authors.lastname: Bertuccio
authors.affiliation: Center for Complex Fluids Engineering and Center for Environmental Implications of Nanotechnology, Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, United States.
authors.forename: Feng
authors.initials: F
authors.lastname: Cao
authors.affiliation: Center for Complex Fluids Engineering and Center for Environmental Implications of Nanotechnology, Department of Civil and Environmental Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, United States.
authors.forename: Gregory V
authors.initials: GV
authors.lastname: Lowry
authors.affiliation: Center for Complex Fluids Engineering and Center for Environmental Implications of Nanotechnology, Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, United States; Center for Complex Fluids Engineering and Center for Environmental Implications of Nanotechnology, Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, United States. Electronic address: tilton@cmu.edu.
authors.forename: Robert D
authors.initials: RD
authors.lastname: Tilton
mesh_terms: D000900:Anti-Bacterial Agents / Q000737:chemistry / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D053768:Metal Nanoparticles / Q000737:chemistry*; D008826:Microbial Sensitivity Tests; D010933:Plankton / Q000166:cytology / Q000187:drug effects* / Q000254:growth & development; D011551:Pseudomonas fluorescens / Q000166:cytology / Q000187:drug effects* / Q000254:growth & development*; D012834:Silver / Q000737:chemistry / Q000494:pharmacology*; D013329:Structure-Activity Relationship; D013499:Surface Properties
chemical_list: D000900:Anti-Bacterial Agents; D012834:Silver
keywords: Antifouling; Antimicrobial surface; Biofilm; Inoculum effect; NanoEHS; Silver nanoparticles; Silver toxicity