## 4 Discussion  
In the last decades, CAPP has been proven as an antimicrobial agent, capable of reducing bacterial and fungal cell viability in mono and multispecies biofilms [13; 14; 22]. In addition, plasma can ameliorate tissue microenvironment with anti-inflammatory and anabolic effects on diverse human cells [23; 24]. There is evidence that plasma can inactivate malignant cells from diverse cancer types [25; 26; 27; 28]. All this favorable evidence led to an increase in the literature on CAPP in medical science and the development of different sources, and set ups, including commercial and experimental devices. The excited species generated in this plasma jet were previously reported with similar parameters [18]. The optical emission spectrum (OES) presented mostly excited nitrogen bands (\(N_{2}\)), ionized nitrogen species (\(N_{2}^{+}\)), produced by helium metastable species, and few helium lines. Excited oxygen species such as OH and atomic O were also present. OES measurements confirm the presence of RNS and ROS that are produced in the plume when plasma interacts with the surrounding ambient air. The spread area of ROS in starch-iodine-agar plates for this plasma jet operating with similar parameters was also investigated in a former study [29]. ROS can diffuse radially outward from the plasma plume where long-lived species, such as ozone, can reach further away or act on the surface for longer time. These reactive species (ROS/RNS) combined with other plasma agents, such as UV radiation, charged particles and helium metastable species can act synergistically leading to microbicide effects. Only a few studies on plasma and periodontal disease or periodontal disease-related biofilms can be found in the literature. _P. gingivalis_ is the most virulent bacterial species associated with periodontal disease development [30; 31]. It is a Gram-negative anaer-obe bacterium that can lead to dysbiosis and changes in host immune response through virulence mechanisms, such as fimbrie, lipopolysaccharideaccharides, capsules, and gingipains (Arg- and Lys-specific proteases) [30; 32]. Fimbirae helps _P. gingivalis_ on biofilm formation, aggregation to oral bacteria and bacterial adhesion to host molecules [30]. _P. gingivalis_ HW24D-1 possess _FimA_ type 2, a gene that encodes a fimbriee protein type that is strongly associated with periodontal disease patients and seems to play a pivotal role as a periodontal-opathogen [31]. This genotype was found to be the most prevalent in sites of periodontitis in a Brazilian population, and can be more virulent, associated with severe periodontitis [33]. A recent study showed a strong relationship between _FimA_ types II and IV and periodontitis, and that the presence of _FimA_ type II increases the colonization  
Figure 3: Frequency histogram of the obtained DNA index (DI) for OBA-9 and HGF cells. P#—minutes of plasma treatment; NT—not-treated; star represents the DI peak in each group. of _P. gingivalis_ in deep periodontal pockets [32]. There is a lack of studies in the literature about the effect of CAPP jet in _FimA_ type 2 _Porplyhormonas_ models. In our study, an experimental setup previously described [34] was used. It worked with He, and a 1.0-m-long flexible polyurethane tube was used for remote generation of the jet. Its antimicrobial potential was previously described against _P. gingivalis_ (ATCC 33277) dual biofilm [13], but we were intrigued about its effect in a more virulent _P. gingivalis_ strain, capable of forming a thick single species biofilm in 48 h (in vitro) and involved in the progression of periodontitis. We detected that He-CAPP jet was capable of reducing cell viability of _P. gingivalis_ HW24D-1 in a time-dependent manner in single species biofilms with significant difference between treated groups and the not-treated group. The results are in accordance with our previous experiments and previous studies in the literature treating _P.