Injections through skin colonized with Staphylococcus aureus biofilm introduce contamination despite standard antimicrobial preparation procedures

Abstract

While surgical site preparation has been extensively studied, there is little information about resistance of skin microbiota in the biofilm form to antimicrobial decontamination, and there are no quantitative models to study how biofilm might be transferred into sterile tissue/implant materials during injections for joint spine and tendon, aspiration biopsies and dermal fillers (DF). In this work, we develop two in vitro models to simulate the process of skin preparation and DF injection using pig skin and SimSkin (silicone) materials, respectively. Using the pig skin model, we tested three of the most common skin preparation wipes (alcohol, chlorhexidine and povidone iodine) and found that during wiping they reduced the biofilm bacterial burden of S. aureus (CFU cm^-2) by three logs with no statistically significant differences between wipes. Using the SimSkin model, we found that transfer of viable bacteria increased with needle diameter for 30G, 25G and 18G needles. Transfer incidence decreased as injection depth was increased from 1 mm to 3 mm. Serial puncture and linear threading injection styles had similar transfer incidence, whereas fanning significantly increased transfer incidence. The results show that contamination of DF during injection is a risk that can be reduced by modifying skin prep and injection practices.

Figure 1. Biofilm model to assess skin preparation.

Figure 2

Simulated injection model (A) and trails in agar showing different injection techniques (B).

Figure 3

Porcine skin planktonic and biofilm bioburden (CFUcm⁻²) before (A) and after (B) skin preparation. CLSM images (Insert, A) of the biomass formed with inoculum density of 10⁵ CFU mL⁻¹. SEM images (Insert, B) show similar textures of preparation pads.

Figure 4. Representative images of bacterial transfer for different injection conditions with the SimSkin model (needle size, depth of placement and planktonic/biofilm bacterial contamination).

Figure 5. Bacterial transfer incidence of porcine skin (2 mm) and SimSkin (1.8 mm) with 18G, 25G and 30G needles and biofilm as initial bioburden.

Confocal fluorescence image stacks (200 μm × 200 μm × 80 μm) of biofilm formed from inoculum of 10⁵ CFU mL⁻¹.

Figure 6. Quantification of bacterial transfer under different injection conditions (needle size/shape, depth of placement, injection techniques and initial bioburden).