Comparative antibacterial activity of N-terminal and C-terminal domains of a recombinant endolysin against Cutibacterium acnes.

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-Cutibacterium acnes phages remains unexplored. In this study, a recombinant endolysin from C. acnes phage CAP 10-3 and its N-terminal and C-terminal domains were tested against C. acnes KCTC 3314 and KCTC 3320 using turbidity reduction and live cell count methods. Starting with an initial OD₆₀₀≈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 C. acnes strains, but it had no significant effect on Staphylococcus aureus KCTC 3881 and only weak activity against Staphylococcus epidermidis CJNU 0702 at high concentrations (100 µg/mL). These findings highlight the N-terminal domain's potential as a selective anti-C. acnes agent with minimal impact on skin flora, supporting its suitability for protein-based antimicrobial therapeutics and cosmetic applications.IMPORTANCECutibacterium acnes is known to play a significant role in the pathology of acne vulgaris and several other disorders. Conventional methods of treating C. acnes 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-C. acnes activity) are also explained. These findings can pave the way for developing alternative peptide-based anti-C. acnes therapeutics.