CLSM images of the plasma treated biofilms.

<p>3D rendered confocal laser scanning micrographs of 3-day <i>P. aeruginosa</i> biofilms, grown on polycarbonate coupons, exposed to the 20 kHz plasma jet for 0s (A and D), 60 s (B and E), and 240 s (C and F). Green colour indicates surviving cells whereas red colour indicates dead cells. Magnification power is 200x (a-c) and 600x (d–f).</p

The plasma jet used in this study.

<p>(A) Schematic diagram of the plasma jet. (B) Photograph of the plasma jet interacting with a biofilm sample.</p

Bacterial growth inhibition zones.

<p><i>P. aeruginosa</i> cell suspensions were spread over MHA plates (9 cm in diameter). The seeded plates were exposed to the 20 kHz plasma jet for (A) 0 s, (B) 120 s, and (C) 240 s and then incubated at 37°C for 24 hours. After incubation, photographs of agar plates, showing bacterial growth inhibition zones, were taken using a digital camera.</p

Percentage cell reduction curves based on colony count method vs. XTT assay.

<p>Percentage cell reduction curves of <i>P. </i>aeruginosa biofilm cells upon exposure to the 20 kHz plasma jet. The dotted line is based on the standard colony count method whereas the solid line is based on the XTT assay. (Each point represents the mean of 3 values ± SE).</p

D-values of 20 kHz and 40 kHz plasma jets against <i>P. aeruginosa</i> biofilm cells.

<p>D-values of 20 kHz and 40 kHz plasma jets against <i>P. aeruginosa</i> biofilm cells.</p

Absorbance of XTT-assay product.

<p>48-hour <i>P. aeruginosa</i> biofilms, grown on Calgary Biofilm Device, were exposed to the 20 kHz plasma jet for up to 4 minutes. After plasma exposure, bacterial cells were dislodged off the pegs into PBS buffer by sonication. 50 µl aliquots of the recovered bacterial suspensions were then mixed with 50 µl of MHB and 20 µl of XTT stock solution and incubated at 37°C for 5 hours. After incubation, the absorbance at 450 nm was measured to quantify XTT metabolic product, the intensity of which is proportional to the number of viable (respiring) cells. (Each point represents the mean of 3 values ± SE).</p

Survival curve of biofilm treated with 20 kHz plasma.

<p>48-hour <i>P. aeruginosa</i> biofilms, grown on Calgary Biofilm Device, were exposed to the 20 kHz plasma jet for up to 4 minutes. The number of biofilm surviving cells in each sample was then calculated using colony count method and used to construct the log survival curve. (Each point represents the mean of 3 values ± SE).</p