## 4 Percentage of _P. gingivalis_ Inhibition with D-CTL Inside the Gel  
Initial assays show a MIC of D-CTL on _P. gingivalis_ of 30 \(\upmu\)g\(\cdot\)mL\({}^{-1}\) and 200 \(\upmu\)g\(\cdot\)mL\({}^{-1}\) for L-CTL (data not shown). After OD control, drops sprayed on Petri dishes confirm the result (Figure 3a). This value may be related to that obtained by [PERSON] and coll. who showed a MIC of 10 \(\upmu\)g\(\cdot\)mL\({}^{-1}\) for D-CTL (and 149 \(\upmu\)g\(\cdot\)mL\({}^{-1}\) for L-CTL) against _P. intermedia_, a similar Gram-negative bacteria found in the case of periimplantitis [49]. Hence, D-CTL is encouraging against periimplant pathogens. As shown with these previous results,  
Figure 2: Adhesion of Alg–Cat gels onto stainless steel plates. (**a**) Behaviour of the Alg–Cat gel during retraction of the upper plate at a speed of 100 \(\upmu\)m\(\cdot\)s\({}^{-1}\); (**b**) force versus time curves for the Alg–Cat gels aged for different durations before the tacking tests, performed at a retraction speed of 100 \(\upmu\)m\(\cdot\)s\({}^{-1}\); (**c**) influence of the aging time and of the retraction speed ((\(\blacksquare\)): 10 \(\upmu\)m\(\cdot\)s\({}^{-1}\), (**d**): 100 \(\upmu\)m\(\cdot\)s\({}^{-1}\), (**e**): 1 mm\(\cdot\)s\({}^{-1}\)) on the specific adhesion energy of the Alg–Cat gels on steel plates. combination of AMP and antibiotic inside Alg-Cat gel could decrease the MIC and reinforce the antibacterial activity. Because L-CTL in Alg-Cat gels showed only a bacteriostatic effect against _P. gingivalis_ in a previous work [31], we decided to focus on D-CTL for antibacterial evaluation. Bacterial supernatant in contact with the D-CTL (at 470 \(\upmu\)g\(\cdot\)mL\({}^{-1}\)) charged gel for 24 h did not grow anymore on the Petri dishes, signing a bactericidal effect of the gel (Figure 3b). [PERSON] et al. estimated a release of CTL out of the gel in range of about 10% (\(m/m\)) of the initially incorporated peptide, namely in this study a concentration of 47 \(\upmu\)g\(\cdot\)mL\({}^{-1}\). It was slightly higher than the measured MIC of 30 \(\upmu\)g\(\cdot\)mL\({}^{-1}\). Interestingly, it was demonstrated that CTL is not toxic [49] and that it is detected in saliva. Most of the secretory proteins of mammalian salivary glands are mainly synthesized and stored in secretory granules of acinar cells and are extruded by exocytosis into saliva via beta-adrenergic receptor activation. CGA was isolated among these proteins [57]. More recently, it was reported that saliva catesatatin could be useful as a biomarker for acute psychological stress in dogs [58]. L-CTL and D-CTL were present in the control group without degradation, mainly in the reduced form (1860 g/mol) (Appendix A Figures A1 and A2a). HPLC analysis shows that peptides released out of the gel, or found inside crushed gel, are not present in the original form (Appendix A Figure A1). Greater peaks analyzed with MALDI-TOF show that CTL is still present, but in a degraded form (Appendix A Figure A2b,c and Table 1). No specific differences between L-CTL and D-CTL fragments were highlighted for all observations. Different molecular weights that were recovered were screened and we tried to affect each of them with a potential sequence of AA derived from the original peptide (web.expasy.org/compute_pi, accessed on 1 October 2021, Table 1). Some of the combinations found were oxidized with one to four oxygen atoms (Figure 4). These oxidation states occur with methionine, phenylalanine and tyrosine residues. CTL-derived peptides were also detected after 7 days (Appendix A Figure A2c). At least five fragments of CTL conserved the LSFR sequence corresponding to the active site of the \(\alpha\)-helix of CTL, that lightened the remnant antimicrobial of the degraded peptide. In the experimental condition corresponding to 24 h, the different released fragments correspond to 12.5% of the initial D-CTL and 25% of the collected material.