Surface micropattern limits bacterial contamination

Abstract

Background: Bacterial surface contamination contributes to transmission of nosocomial infections. Chemical cleansers used to control surface contamination are often toxic and incorrectly implemented. Additional non-toxic strategies should be combined with regular cleanings to mitigate risks of human error and further decrease rates of nosocomial infections. The Sharklet micropattern (MP), inspired by shark skin, is an effective tool for reducing bacterial load on surfaces without toxic additives. The studies presented here were carried out to investigate the MP surfaces capability to reduce colonization of methicillin-sensitive Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA) compared to smooth control surfaces.

Methods: The MP and smooth surfaces produced in acrylic film were compared for remaining bacterial contamination and colonization following inoculation. Direct sampling of surfaces was carried out after inoculation by immersion, spray, and/or touch methods. Ultimately, a combination assay was developed to assess bacterial contamination after touch transfer inoculation combined with drying (persistence) to mimic common environmental contamination scenarios in the clinic or hospital environment. The combination transfer and persistence assay was then used to test antimicrobial copper beside the MP for the ability to reduce MSSA and MRSA challenge.

Results: The MP reduced bacterial contamination with log reductions ranging from 87-99% (LR = 0.90-2.18; p < 0.05) compared to smooth control surfaces. The MP was more effective than the 99.9% pure copper alloy C11000 at reducing surface contamination of S. aureus (MSSA and MRSA) through transfer and persistence of bacteria. The MP reduced MSSA by as much as 97% (LR = 1.54; p < 0.01) and MRSA by as much as 94% (LR = 1.26; p < 0.005) compared to smooth controls. Antimicrobial copper had no significant effect on MSSA contamination, but reduced MRSA contamination by 80% (LR = 0.70; p < 0.005).

Conclusion: The assays developed in this study mimic hospital environmental contamination events to demonstrate the performance of a MP to limit contamination under multiple conditions. Antimicrobial copper has been implemented in hospital room studies to evaluate its impact on nosocomial infections and a decrease in HAI rate was shown. Similar implementation of the MP has potential to reduce the incidence of HAIs although future clinical studies will be necessary to validate the MP's true impact.

Figure 1

Scanning electron micrograph of Sharklet micro-patterned (MP) acrylic material. The scale bar in the micrograph represents 20 μm.

Figure 2

Microbial attachment. MSSA and MRSA were incubated in suspension on smooth (black bars) or micro-patterned (grey bars) acrylic film for 1 h. After rinsing 3 times and drying for 1 h the remaining viable bacteria on the surfaces were quantified. The plot represents average log densities and standard error of the mean. Significance was determined using a single t-Test of the log reduction data points. The average log reduction values were then used to calculate the median percent reduction values indicated above each column. p < 0.005 (***).

Figure 3

Microbial persistence. Smooth and micro-patterned (MP) acrylic films were challenged with a sprayed inoculum and dried for 30 m. A.) Log densities of bacteria present on the surfaces of the MP compared to smooth controls for MSSA are plotted with the associated standard error of the mean. B.) A representative image of a RODAC contact plate after MSSA sampling, the MP surface (right) has fewer bacteria compared to the smooth surface (left). p < 0.005 (***) n = 3.

Figure 4

Comparison of Sharklet MP to Copper antimicrobial surface. MSSA and MRSA were used to challenge smooth unpatterned film, the MP film, and copper foil (99.9% pure) using a touch incident with time points sampled after 0 and 90 m of drying. Average log density values are presented for smooth, the MP, and copper surfaces. Error bars represent the SEM for 3 independent experiments. The percent reduction values were calculated using individual log reduction values comparing either Sharklet MP or copper to smooth control samples. p < 0.05 (*), p < 0.01 (**), p < 0.005 (***).