pH-Controlled Cerium Oxide Nanoparticle Inhibition of Both Gram-Positive and Gram-Negative Bacteria Growth

Abstract

Here, the antibacterial activity of dextran-coated nanoceria was examined against Pseudomonas aeruginosa and Staphylococcus epidermidis by varying the dose, the time of treatment, and the pH of the solution. Findings suggested that dextran-coated nanoceria particles were much more effective at killing P. aeruginosa and S. epidermidis at basic pH values (pH = 9) compared to acidic pH values (pH = 6) due to a smaller size and positive surface charge at pH 9. At pH 9, different particle concentrations did cause a delay in the growth of P. aeruginosa, whereas impressively S. epidermidis did not grow at all when treated with a 500 μg/mL nanoceria concentration for 24 hours. For both bacteria, a 2 log reduction and elevated amounts of reactive oxygen species (ROS) generation per colony were observed after 6 hours of treatment with nanoceria at pH 9 compared to untreated controls. After 6 hours of incubation with nanoceria at pH 9, P. aeruginosa showed drastic morphological changes as a result of cellular stress. In summary, this study provides significant evidence for the use of nanoceria (+4) for a wide range of anti-infection applications without resorting to the use of antibiotics, for which bacteria are developing a resistance towards anyway.

Antibacterial mechanism and activity of cerium oxide nanoparticles

“…As discussed in the last section, the reversible conversion between Ce(III) and Ce(IV) is the cause of ROS generation. He et al [52] found a notable increase in the intracellular ROS level upon the exposure to 100 and 200 mg mL −1 CeO 2 NPs in normal saline (NS: 0.9% NaCl; pH 6.8) medium within 2 h. Alpaslan et al [56] reported that the quantity of generated ROS elevated in both Pseudomonas aeruginosa (P. aeruginosa) and…”

“…The impact of dispersing medium (along with the pH) on the antibacterial behavior is essentially attributed to the electrostatic interaction, which means the acidity/basicity of the suspension will affect the surface charge on NPs, and finally lead to the variation of interaction between NPs and bacteria. Alpaslan et al [56] reported that the positive charged dextran-coated CeO 2 NPs in pH 9 medium had relatively stronger interaction with the bacterial membrane, whereas in pH 6 medium, the surface charge of NPs became negative (−8.75 mV) and led to the decrease of the antibacterial efficiency. This variation in surface charge can be measured by zeta potential (Fig.…”

“…In this regard, a surface coating consisting of macromolecules and polymers can provide a protective shell for CeO 2 NPs, enhance the dispersibility in aqueous media and improve its biocompatibility. The hydrophilic and biocompatible dextran-coated CeO 2 NPs have already been synthesized with enhanced stability in aqueous solution [56]. Wang et al [78] suggested that both dextran-and polyacrylic acid-coated CeO 2 NPs exhibited strong inhibition to the P. aeruginosa.…”

“…Zeta potential of 0.1 mol L −1 dextran coated cerium oxide NPs dispersed in PBS at pH 6 and pH 9. Reproduced with the permission from Ref [56]…”

Chitosan-coated cerium oxide nanoparticles and sparfloxacin encapsulated polymersomes as a new drug system with antimicrobial properties

“…Due to their charged surface and high surface area, NPs tend to aggregate into clusters that can be several micrometers in diameter. 24 This is also the case with CeNPs. To solve this problem, polymer encapsulation of the CeNPs is an ideal method.…”