Antibiofilm and Membrane-Damaging Potential of Cuprous Oxide Nanoparticles against Staphylococcus aureus with Reduced Susceptibility to Vancomycin

Abstract

The antimicrobial effects of copper ions and salts are well known, but the effects of cuprous oxide nanoparticles (Cu 2 O-NPs) on staphylococcal biofilms have not yet been clearly revealed. The present study evaluated Cu 2 O-NPs for their antibacterial and antibiofilm activities against heterogeneous vancomycin-intermediate Staphylococcus aureus (hVISA) and vancomycin-intermediate S. aureus (VISA). Nanoscaled Cu 2 O, generated by solution phase technology, contained Cu 2 O octahedral nanoparticles. Field emission electron microscopy demonstrated particles with sizes ranging from 100 to 150 nm. Cu 2 O-NPs inhibited the growth of S. aureus and showed antibiofilm activity. The MICs and minimum biofilm inhibitory concentrations ranged from 625 g/ml to 5,000 g/ml and from 2,500 g/ml to 10,000 g/ml, respectively. Exposure of S. aureus to Cu 2 O-NPs caused leakage of the cellular constituents and increased uptake of ethidium bromide and propidium iodide. Exposure also caused a significant reduction in the overall vancomycin-BODIPY (dipyrromethene boron difluoride [4,4-difluoro-4-bora-3a,4a-diaza-s-indacene] fluorescent dye) binding and a decrease in the viable cell count in the presence of 7.5% sodium chloride. Cu 2 O-NP toxicity assessment by hemolysis assay showed no cytotoxicity at 625 to 10,000 g/ml concentrations. The results suggest that Cu 2 O-NPs exert their action by disruption of the bacterial cell membrane and can be used as effective antistaphylococcal and antibiofilm agents in diverse medical devices. Biofilm formation, one of the defense mechanisms of Staphylococcus aureus, represents a structural community of bacterial cells embedded in a self-produced polymeric matrix adherent to an artificial surface (1). Biofilms can be associated with a variety of complications, the worst being the risk of bacterial and fungal infections in surgical implanted devices. Bacteria embedded in biofilms are hard to eradicate with standard antibiotics and are intrinsically resistant to host immune responses (2). S. aureus strains with reduced susceptibility to vancomycin, such as heterogeneous vancomycin-intermediate Staphylococcus aureus (hVISA) and vancomycin-intermediate Staphylococcus aureus (VISA), are being reported increasingly worldwide (3). The emergence of such strains is attributed to excess or irrational use of vancomycin and poor tissue penetration (4). Biofilm formation also plays an important role in the pathogenesis of staphylococcal infections, especially with prosthetic materials (5). It is presumed to be a significant initial step in the pathway to development of vancomycin resistance (6, 7). Biofilm infections are difficult to treat due to their inherent antibiotic resistance (8). Only limited numbers of antibiotics, such as daptomycin, quinupristin-dalfopristin, linezolid, and tigecycline, are active against the vancomycin-nonsusceptible S. aureus strains (9). Interestingly, daptomycin nonsusceptibility is also being reported for some hVISA and VISA isolates (10, 11). Despite antimicrobial therapy, the ...

Green electrospun nanocuprous oxide–poly(ethylene oxide)–silk fibroin composite nanofibrous scaffolds for antibacterial dressings

“…According to theoretical calculation, when the concentration of Cu 2 O was 5 mg/mL, the content of nano‐Cu 2 O was about 20 μg in 1 mg of nano‐Cu 2 O–SF–PEO CNSs, and these were wrapped in nanofibers. The release of small amounts of nano‐Cu 2 O showed no cytotoxicity …”

“…Gram‐positive S. aureus usually tends to cause biofilm infections in damaged tissues during the early stages of infection. In the later stage, Gram‐negative E. coli is apt to result in subsequent infection . It is very necessary to impart antibacterial properties in wound dressings.…”

“…The reason may have been that the surface of the nanofibrous scaffolds with a high surface‐to‐volume ratio prominently affected the interactions with bacterial cells and improved bacterial cell adhesion; this caused the isolation of the bacteria from the environment. On the other hand, the Cu 2 O NPs adhered to the surface of the microbial cells and changed the cell membrane structure; this resulted in the destruction of the permeation barrier of the microbial membrane structure …”

“…Generally, Cu(I) and metallic Cu have presented higher antibacterial properties than Cu(II) . It was reported that nano‐Cu 2 O showed no cytotoxicity against human tissues at lower concentrations . Singh et al .…”

“…It was reported that nano‐Cu 2 O showed no cytotoxicity against human tissues at lower concentrations . Singh et al . reported that nano‐Cu 2 O showed no cytotoxicity at 625 to 10,000 μg/mL concentrations via a hemolysis assay.…”