Comparative antibacterial activity of N-terminal and C-terminal domains of a recombinant endolysin against <i>Cutibacterium acnes</i>

Endolysins are promising antibacterial agents due to their selective antibacterial activity and minimal risk of resistance. The antibacterial activity of individual domains of endolysins from anti-<i>Cutibacterium acnes</i> phages remains unexplored. In this study, a recombinant endolysin from <i>C. acnes</i> phage CAP 10-3 and its N-terminal and C-terminal domains were tested against <i>C. acnes</i> KCTC 3314 and KCTC 3320 using turbidity reduction and live cell count methods. Starting with an initial OD₆₀₀<b>≈</b>1, a 3 h treatment with 50 µg/mL of the N-terminal domain (N1) reduced OD₆₀₀ to 0.395 (KCTC 3314) and 0.324 (KCTC 3320), while that of full-length (FL) reduced OD₆₀₀ to 0.547 and 0.474, respectively. Correspondingly, N1 reduced viable counts by 1.13-1.35 log, whereas FL showed 0.94-0.95 log reduction, confirming N1's stronger bactericidal effect. C-terminal domain exhibited minimal changes in both OD₆₀₀ and cell count values. N1's lytic effect was further confirmed by morphology analysis. Therefore, the N-terminal domain was further characterized for its activity and specificity. It showed dose-dependent activity against both <i>C. acnes</i> strains, but it had no significant effect on <i>Staphylococcus aureus</i> KCTC 3881 and only weak activity against <i>Staphylococcus epidermidis</i> CJNU 0702 at high concentrations (100 µg/mL). These findings highlight the N-terminal domain's potential as a selective anti-<i>C</i>. <i>acnes</i> agent with minimal impact on skin flora, supporting its suitability for protein-based antimicrobial therapeutics and cosmetic applications.IMPORTANCE<i>Cutibacterium acnes</i> is known to play a significant role in the pathology of acne vulgaris and several other disorders. Conventional methods of treating <i>C. acnes</i> infections using antibiotics face an ever-aggravating antibiotic resistance challenge. Endolysins present a promising alternative with advantages such as specificity and low-to-no chances of resistance. The current study compares the antibacterial activity of the full length as well as its N- and C-terminal domains of an endolysin from phage CAP 10-3. In addition, the dose-dependent effect and specificity of the N-terminal domain (which showed the most significant anti-<i>C</i>. <i>acnes</i> activity) are also explained. These findings can pave the way for developing alternative peptide-based anti-<i>C</i>. <i>acnes</i> therapeutics.