Antibiotic-Polyphosphate Nanocomplexes: A Promising System for Effective Biofilm Eradication

Dennis To,1 Mariana Blanco Massani,1 Débora C Coraça-Huber,2 Anna Seybold,3 Fabrizio Ricci,1,4 Katrin Zöller,1 Andreas Bernkop-Schnürch1 1Center for Chemistry and Biomedicine, Department of Pharmaceutical Technology, Institute of Pharmacy, University of Innsbruck, Innsbruck, Austria; 2Research Laboratory for Implant Associated Infections (BIOFILM LAB), Experimental Orthopaedics, University Hospital for Orthopaedics and Traumatology, Medical University Innsbruck, Innsbruck, Austria; 3Department of Zoology, University of Innsbruck, Innsbruck, Austria; 4Thiomatrix Forschungs- und Beratungs GmbH, Innsbruck, AustriaCorrespondence: Andreas Bernkop-Schnürch, Email Andreas.Bernkop@uibk.ac.atPurpose: The eradication of bacterial biofilms poses an enormous challenge owing to the inherently low antibiotic susceptibility of the resident microbiota. The complexation of antibiotics with polyphosphate can substantially improve antimicrobial performance.Methods: Nanoparticular complexes of the model drug colistin and polyphosphate (CP-NPs) were developed and characterized in terms of their particle size and morphology, polydispersity index (PDI), zeta potential, and cytotoxicity. Enzyme-triggered monophosphate and colistin release from the CP-NPs was evaluated in the presence of alkaline phosphatase (AP). Subsequently, antimicrobial efficacy was assessed by inhibition experiments on planktonic cultures, as well as time-kill assays on biofilms formed by the model organism Micrococcus luteus.Results: The CP-NPs exhibited a spherical morphology with particle sizes < 200 nm, PDI < 0.25, and negative zeta potential. They showed reduced cytotoxicity toward two human cell lines and significantly decreased hemotoxicity compared with native colistin. Release experiments with AP verified the enzymatic cleavage of polyphosphate and subsequent release of monophosphate and colistin from CP-NPs. Although CP-NPs were ineffective against planktonic M. luteus cultures, they showed major activity against bacterial biofilms, outperforming native colistin treatment. Strongly elevated AP levels in the biofilm state were identified as a potential key factor for the observed findings.Conclusion: Accordingly, polyphosphate-based nanocomplexes represent a promising tool to tackle bacterial biofilm. Keywords: polyphosphate, colistin, antimicrobial, nanoparticle, nanocomplex