Antimicrobial Activity of Antimicrobial Peptides Against Aggregatibacter Actinomycetemcomitans

Objectives: Antimicrobial peptides (AMPs) have shown promising potential as a new therapeutic approach against bacterial infection. However, there is no report on the killing activities of LL-37 (cathelicidin derived peptide), Lactoferrin chimera (LFchimera, harbouring the two known antimicrobial domains of bovine lactoferrin) and IDR-1018 (Innate Defense Regulator peptide) against periodontopathic bacteria compared to minocycline hydrochloride (MH), a conventional antibiotic used in periodontal treatment. Therefore, this study aimed to determine in vitro antimicrobial activities of those antimicrobial agents against Aggregatibacter actinomycetemcomitans.
Methods: The killing activities of various concentrations of LL-37, LFchimera, IDR-1018 and MH against A. actinomycetemcomitans were determined by colony culturing assay. Each agent was added to the bacterial suspension to a final concentration of 1, 5, 10, 20, 40 and 50 µM and incubated at 37^oC, 5% CO₂ for 1 h. Then the viability of bacterial cells was determined by plate count technique. A bacterial suspension without antimicrobial agents served as a control. The percentage killing effects of each agent was calculated using the formula [1 - (CFU sample/CFU control)] x 100%.
Results: The results revealed that the killing effects of all agents on A. actinomycetemcomitans appeared to be dose-related. The antimicrobial activities of all AMPs range from 13-100%. In contrast, MH at low concentrations (1 and 5 μM) not only showed no killing activity but also stimulate growth of the bacteria. All concentrations of LL-37 and LFchimera exhibited higher antimicrobial activities than MH. Among all agents tested, all concentrations of LFchimera possessed strongest killing activity towards A. actinomycetemcomitans and significant higher activities than MH (P < 0.05).
Conclusions: Altogether, the results obtained indicate that LFchimera displayed strongest killing activity towards A. actinomycetemcomitans and should be considered for development as a new potential therapeutic agent that may be used as an adjunctive treatment for periodontitis.