Comparison of Methods for Evaluation of the Bactericidal Activity of Copper-Sputtered Surfaces against Methicillin-Resistant Staphylococcus aureus

Abstract

Bacteria can survive on hospital textiles and surfaces, from which they can be disseminated, representing a source of health careassociated infections (HCAIs). Surfaces containing copper (Cu), which is known for its bactericidal properties, could be an efficient way to lower the burden of potential pathogens. The antimicrobial activity of Cu-sputtered polyester surfaces, obtained by direct-current magnetron sputtering (DCMS), against methicillin-resistant Staphylococcus aureus (MRSA) was tested. The Cupolyester microstructure was characterized by high-resolution transmission electron microscopy to determine the microstructure of the Cu nanoparticles and by profilometry to assess the thickness of the layers. Sputtering at 300 mA for 160 s led to a Cu film thickness of 20 nm (100 Cu layers) containing 0.209% (wt/wt) polyester. The viability of MRSA strain ATCC 43300 on Cusputtered polyester was evaluated by four methods: (i) mechanical detachment, (ii) microcalorimetry, (iii) direct transfer onto plates, and (iv) stereomicroscopy. The low efficacy of mechanical detachment impeded bacterial viability estimations. Microcalorimetry provided only semiquantitative results. Direct transfer onto plates and stereomicroscopy seemed to be the most suitable methods to evaluate the bacterial inactivation potential of Cu-sputtered polyester surfaces, since they presented the least experimental bias. Cu-polyester samples sputtered for 160 s by DCMS were further tested against 10 clinical MRSA isolates and showed a high level of bactericidal activity, with a 4-log 10 reduction in the initial MRSA load (10 6 CFU) within 1 h. Cu-sputtered polyester surfaces might be of use to prevent the transmission of HCAI pathogens.

ZrNO–Ag co-sputtered surfaces leading to E. coli inactivation under actinic light: Evidence for the oligodynamic effect

“…The E. coli and MRSA viability as a function of time was monitored by direct transfer on plate and by stereomicroscopy. These two methods were used to determine the bacterial viability because they imply a very low experimental bias [28,29]. No bacterial regrowth was observed after bacterial inactivation.…”

“…Antimicrobial Ag-nanoparticles (NPs) have sputtered [9,18,28,29] on different textiles due to the known disinfecting properties of Ag. Ag is also used in healing wound-pads [4][5][6], and implants [1].…”

“…Magnetron sputtering has been used to deposit thin metal/oxide films (or combinations thereof) inducing self-cleaning and antibacterial properties in natural fibers like cotton and artificial textiles like polyester [14,15,28,29,37]. The present study addresses: (a) the sputtering of ZrNO and ZrNO-Ag films on polyester optimizing the sputtering chamber gas atmosphere to attain the fastest E. coli bacterial inactivation kinetics, (b) the performance of ZrNO-Ag films obtained either by sputtering sequentially Ag after Zr or by co-sputtering of both components, (c) the bacterial inactivation kinetics by ZrNO and ZrNO-Ag films under low intensity actinic light and finally (d) the characterization of the microstructure of ZrNO and ZrNO-Ag films by X-ray fluorescence (XRF), diffuse reflectance spectroscopy (DRS), atomic force microscopy (AFM), contact angle (CA) and transmission electron microscopy (TEM).…”

Comparison of HIPIMS sputtered Ag- and Cu-surfaces leading to accelerated bacterial inactivation in the dark

“…This leads to higher reactivity and possibly to higher cell death rate. Smaller metal lattice constants have been reported by XRD for the HIPIMS layers compared to DCMS layers usually deposited using lower energies [25][26][27][28][29][30][31][32][33]. The HIPIMS runs show that with increasing current, the Ar 2+ and Cu 2+ in the gas phase increase.…”

“…The inoculated coupons were placed in a 2 mL Eppendorf containing 1 mL NaCl 0.9% and bacteria were detached by vortexing (3 min). Bacterial counts were performed by plating the re-suspended bacteria on BHI agar-plates [33].…”