# Anti-Bacterial Action of Plasma Multi-Jets in the Context of Chronic Wound Healing
## 3 Results
### Inactivation of Staphylococcus aureus
One may suspect that besides the reactive species delivery and action on bacteria, the bacteria on the central zone of the plasma jet impact zone will rapidly be inactivated as there the electric field strength is large enough, while those on the more outer locations will require the accumulation of a larger number of electric field pulses of lower strength. Such combinatory and threshold-dependent action of pulsed electric field with reactive species was recently reported [48; 58; 59; 60; 61] during plasma treatment of various cell lines. Second, the inhibition diameters are no longer larger for the four central multi-jets but for the 12 s multi-jets distributed on the 18 mm in diameter ring, conversely to the results obtained with the multi-spot applicator in Figure 7.  
Third, the yellow color, representative for the _S. aureus_ colonization, is less intense in between the multi-jet impact regions in Figure 8 than it was in Figure 7. This indicates that the growth of bacterial lawn even in the region in between the multi-spots is reduced with the diffuse mode applicator, presumably because of the reactive species' diffusion from impact plasma points thanks to the additional sleeve. These two latter observations reveal that the diffuse mode applicator modifies the relative bactericidal efficiency of the individual multi-jets and that the whole surface of the sample is plasma-treated and partly inactivated even though the multi-jets are much more effective than the diffuse plasma. In the context of wound treatment, the delivery of plasma can be planned for two different scenarios. The first would be to prevent either bacteria colonization right after the wound occurrence or bacteria re-colonization following the disinfecting care of a persisting wound. This was the motivation of the previous documented results in Figures 7 and 8, where the plasma delivery was performed right after the bacteria inoculation on the agar sample. The second and most critical need for alternative treatment, likely plasma-based, is for infected or chronic wound situations where the bacterial colonization is already achieved. To assess the potential action of plasma multi-jets for this second scenario, Figure 8e presents the 10-min-long treatment performed on a mature bacterial lawn, obtained after a 24 h incubation of the inoculated membrane on the agar substrate. It is observed that the diffuse mode applicator induces some bactericidal effect on the mature bacterial lawn. Partly inhibited multi-spots are observed together with a slightly less yellow colored lawn in the center than in the peripheral regions of the sample. Inactivation of Pseudomonas aeruginosa ATCC(r)9027 TM and Resistant Pseudomonas aeruginosa Cultured from Patient's Sampling  
Figure 9 presents treatment time dependence with the diffuse mode plasma applicator for the _P. aeruginosa_ ATCC(r)9027 TM and resistant _P. aeruginosa_ inoculated membrane set on agar substrates. As obtained with the _S. aureus_ in Figure 8, the use of the diffuse mode applicator for 1, 5 and 10 min results in the inactivation of the two _P. aeruginosa_ strains. It is again observed that the inactivation spot diameter, associated with each single jet, increases with the treatment duration, and that the bacteria lawn growth is also reduced in the region in between these spots, where the diffuse plasma is active. Two main additional observations can be made. First, it is quantitatively shown that the multi-jets-based treatment is more efficient for the two _P. aeruginosa_ strains than for _S. aureus_. Second, it is noticeable that the multi-jet-based treatment is as efficient for the regular as it is for the resistant strain, clearly differencing the plasma action from other conventional strategies based on antibiotics supply.