Synergy between Synthetic Antimicrobial Polymer and Antibiotics: A Promising Platform To Combat Multidrug-Resistant Bacteria.

The failure of many antibiotics in the treatment of chronic infections caused by multidrug-resistant (MDR) bacteria necessitates the development of effective strategies to combat this global healthcare issue. Here, we report an antimicrobial platform based on the synergistic action between commercially available antibiotics and a potent synthetic antimicrobial polymer that consists of three key functionalities: low-fouling oligoethylene glycol, hydrophobic ethylhexyl, and cationic primary amine groups. Checkerboard assays with Pseudomonas aeruginosa (P. aeruginosa) and Escherichia coli demonstrated synergy between our synthetic antimicrobial polymer and two antibiotics, doxycycline and colistin. Coadministration of these compounds significantly improved the bacteriostatic efficacy especially against MDR P. aeruginosa strains PA32 and PA37, where the minimal inhibitory concentrations (MICs) of polymer and antibiotics were reduced by at least 4-fold. A synergistic killing activity was observed when the antimicrobial polymer was used in combination with doxycycline, killing >99.999% of planktonic and biofilm P. aeruginosa PAO1 upon a 20 min treatment at a polymer concentration of 128 µg mL-1 (4.6 µM) and doxycycline concentration of 64 µg mL-1 (133.1 µM). In addition, this synergistic combination reduced the rate of resistance development in P. aeruginosa compared to individual compounds and was also capable of reviving susceptibility to treatment in the resistant strains.

Antibiofilm Nitric Oxide-Releasing Polydopamine Coatings.

The growing number of patient morbidity related to nosocomial infections has placed an importance on the development of new antibacterial coatings for medical devices. Here, we utilize the versatile adhesion property of polydopamine (pDA) to design an antibacterial coating that possesses low-fouling and nitric oxide (NO)-releasing capabilities. To demonstrate this, glass substrates were functionalized with pDA via immersion in alkaline aqueous solution containing dopamine, followed by grafting of low-fouling polymer (poly(ethylene glycol) (PEG)) via Michael addition and subsequent formation of N-diazeniumdiolate functionalities (NO precursors) by purging with NO gas. X-ray photoelectron spectroscopy confirmed the successful grafting of PEG and formation of N-diazeniumdiolate on polydopamine-coated substrates. NO release from the coating was observed over 2 days, and NO loading is tunable by the pDA film thickness. The antibacterial efficiency of the coatings was assessed using Gram-negative Pseudomonas aeruginosa (i.e., wild-type PAO1 and multidrug-resistant PA37) and Gram-positive Staphylococcus aureus (ATCC 29213). The NO-releasing PEGylated pDA film inhibited biofilm attachment by 96 and 70% after exposure to bacterial culture solution for 24 and 36 h, respectively. In contrast, films that do not contain NO failed to prevent biofilm formation on the surfaces at these time points. Furthermore, this coating also showed 99.9, 97, and 99% killing efficiencies against surface-attached PAO1, PA37, and S. aureus bacteria. Overall, the combination of low-fouling PEG and antibacterial activity of NO in pDA films makes this coating a potential therapeutic option to inhibit biofilm formation on medical devices.

S-Nitrosothiol Plasma-Modified Surfaces for the Prevention of Bacterial Biofilm Formation.

The development of novel strategies for the prevention of bacterial infections is of utmost importance because of the exponential growth in the number of patient morbidity related to nosocomial and chronic infections. Nitric oxide (NO) is known to be a potent inhibitor of bacterial growth and adhesion to surfaces. Here, we develop an antibiofilm coating that possesses S-nitrosothiol NO donors via plasma polymerization (PP) for biofilm prevention applications. Cell culture dishes of four different film thicknesses ranging from 125 to 1000 nm were coated via PP using a thiol monomer. The thiol functionality on the substrates was converted to S-nitrosothiol NO precursors using tert-butyl nitrite. The successful conjugation of thiol and subsequent formation of S-nitrosothiol functionalities on the substrates were confirmed using X-ray photoelectron spectroscopy and UV-vis analysis. These coatings are capable of releasing NO over 2 days, and the NO loading is tunable by the polymer film thickness. The antibiofilm activity of the surfaces was assessed using Gram-negative bacteria, Pseudomonas aeruginosa. Higher film thickness (and hence, higher NO loading) demonstrate better antibiofilm activity, and the best performing coating shows 81 and 60% inhibition of bacterial attachment to the surface after exposure to bacterial culture solution for 24 and 36 h, respectively. Overall, the NO-releasing plasma-modified surfaces present a potential viable strategy to inhibit bacterial biofilm formation.

Exploiting the Versatility of Polydopamine-Coated Nanoparticles to Deliver Nitric Oxide and Combat Bacterial Biofilm.

In this study, an antimicrobial platform in the form of nitric oxide (NO) gas-releasing polydopamine (PDA)-coated iron oxide nanoparticles (IONPs) is developed for combating bacterial biofilms. NO is bound to the PDA-coated IONPs via the reaction between NO and the secondary amine moieties on PDA to form N-diazeniumdiolate (NONOate) functionality. To impart colloidal stability to the nanoparticles in aqueous solutions (e.g., phosphate buffered saline (PBS) and bacteria cell culture media M9), a polymer bearing hydrophilic and amine pendant groups, P(OEGMA)-b-P(ABA), is synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization and is subsequently grafted onto the PDA-coated IONPs by employing the Schiff base/Michael addition reaction between o-quinone and a primary amine. These nanoparticles are able to effectively disperse Pseudomonas aeruginosa biofilms (up to 79% dispersal) at submicromolar NO concentrations. In addition, the nanoparticles demonstrate excellent bactericidal activity toward P. aeruginosa planktonic and biofilm cells (up to 5-log10 reduction).

Recent advances in nitric oxide delivery for antimicrobial applications using polymer-based systems.

The nitric oxide (NO) molecule has gained increasing attention in biological applications to combat biofilm-associated bacterial infections. However, limited NO loading, relatively short half-lives of low molecular weight NO donor compounds, and difficulties in targeted delivery of NO have hindered their practical clinical administration. To overcome these drawbacks, the combination of NO and scaffolds based on biocompatible polymers is an effective way towards realizing the practical utility of NO in biomedical applications. In this regard, the present overview highlights the recent developments in NO-releasing polymeric biomaterials for antimicrobial applications, focusing on antibiofilm treatments and the challenges that need to be overcome.

Nitric Oxide-Loaded Antimicrobial Polymer for the Synergistic Eradication of Bacterial Biofilm.

Bacterial biofilms are often difficult to treat and represent the main cause of chronic and recurrent infections. In this study, we report the synthesis of a novel antimicrobial/antibiofilm polymer that consists of biocompatible oligoethylene glycol, hydrophobic ethylhexyl, cationic primary amine, and nitric oxide (NO)-releasing functional groups. The NO-loaded polymer has dual-action capability as it can release NO which triggers the dispersion of biofilm, whereas the polymer can induce bacteria cell death via membrane wall disruption. By functionalizing the polymers with NO, we observed a synergistic effect in biofilm dispersal, planktonic and biofilm killing activities against Pseudomonas aeruginosa. The NO-loaded polymer results in 80% reduction in biofilm biomass and kills >99.999% of planktonic and biofilm P. aeruginosa cells within 1 h of treatment at a polymer concentration of 64 µg mL-1. To achieve this synergistic effect, it is imperative that the NO donors and antimicrobial polymer exist as a single chemical entity, instead of a cocktail physical mixture of two individual components. The excellent antimicrobial/antibiofilm activity of this dual-action polymer suggests the advantages of combination therapy in combating bacterial biofilms.

Biofilm dispersal using nitric oxide loaded nanoparticles fabricated by photo-PISA: influence of morphology.

Polymeric nanoparticles (NPs) of different morphologies (spheres and worms) were synthesized using a visible light mediated polymerization-induced self-assembly (PISA) approach. Spherical and worm-like NPs were subsequently modified to generate diazeniumdiolate functionalized NPs. Interestingly, the NO release rate and the dispersal of biofilms were found to strongly depend on the NP morphology. NPs with a higher aspect ratio (worms) exhibited a slower NO release rate and greater biofilm dispersal after 1 h of incubation.