Fig 1.
Schematic of the electrical treatment device.
Electrodes were placed 3 mm away from the disc. The drawing was originally published in [20].
Fig 2.
Confocal microscopy of biofilms after 24 hours of no exposure (left) or exposure (right) to direct current (DC).
S. aureus control (A) and 200 μA DC (B); S. epidermidis control (C) and 200 μA DC (D); P. aeruginosa control (E) and 200 μA DC (F). All images were taken at 60X magnification; a minimum of seven fields were observed. A representative field for each bacterial biofilm sample is shown.
Table 1.
Mean bacterial biofilm quantities and LRF values at 24 hours (n = 3 for all samples).
Fig 3.
Scanning electron micrographs of biofilm-laden discs exposed to 200 μA direct current (DC) or no exposure for 24 hours.
S. aureus control (A) or 200 μA DC (B); S. epidermidis control (C) or 200 μA DC D); P. aeruginosa control (E) or 200 μA DC (F). All images were taken at 10K magnification and a minimum of three fields were observed. A representative field for each bacterial biofilm sample is shown.
Table 2.
Mean bacterial biofilm quantities and LRF values.
Fig 4.
Flow cytometric analysis of biofilms exposed to 200 μA direct current (DC) for 24 hours, and controls.
S. aureus control (A) and DC exposure (B); S. epidermidis control (C) and DC exposure (D); and P. aeruginosa control (E) and DC exposure (F). Experiments were performed in triplicate for each organism; a representative graph is shown for each bacterium.
Fig 5.
Detection of reactive oxygen species (ROS) using nitroblue tetrazolium.
Samples not exposed to current (shown as 0 μA) were compared with those exposed to 200 μA direct current (DC) after 5 and 10 minutes. A. ROS production in S. aureus *p = 0.0088; B. S. epidermidis *p = 0.0088 **p = 0.012; and C. P. aeruginosa *p = 0.009, compared with control.
Fig 6.
Pre-treating buffer with 2,000 μA direct current (DC) did not affect S. aureus and P. aeruginosa and slightly affected S. epidermidis over a period of 24 hours.
A. S. aureus biofilms B. S. epidermidis biofilms *p = 0.0463; C. P. aeruginosa biofilms. Samples not exposed to DC are shown as 0 μA.
Table 3.
Concentrations of catalase and superoxide dismutase increase in response to DC.
Table 4.
Supplementation of bacterial biofilms with catalase, D-mannitol or Tempol protects against the electricidal effect.
Fig 7.
The electricidal effect is enhanced in PAO1ΔsodAB.
P. aeruginosa PAO1ΔsodAB compared with parental control following exposure to 200 μA direct current (DC) for 24 hours, *p = 0.0495, n = 3 for all samples. Samples not exposed to DC are shown as 0 μA.
Fig 8.
Lipid peroxidation in response to DC.
Lipid peroxidation measured by MDA production in S. aureus (A), S. epidermidis (B) and P. aeruginosa (C) following no exposure (shown as 0 μA) or exposure to 200 μA direct current for 5 or 10 minutes. Samples were read in triplicate and normalized to the log10 cfu/cm2.
Table 5.
Transcript changes in P. aeruginosa PAO1 in response to direct current.