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The aims of this study were to describe the synthesis of a novel synthetic peptide based on the primary structure of the KR-12 peptide and to evaluate its antimicrobial and anti-biofilm activities against Streptococcus mutans. The antimicrobial effect of KR-12 and [W]KR12-KAEK was assessed by determining the minimum inhibitory (MIC) and minimum bactericidal (MBC) concentrations. The evaluation of anti-biofilm activity was assessed through total biomass quantification, colony forming unit counting and scanning electron microscopy. [W]KR12-KAEK showed MIC and MBC values ranging from 31.25 to 7.8 and 62.5 to 15.6 μg ml, respectively. Furthermore, [W7]KR12-KAEK significantly reduced biofilm biomass (50-100%). Regarding cell viability, [W]KR12-KAEK showed reductions in the number of CFUs at concentrations ranging from 62.5 to 7.8 μg ml and 500 to 62.5 μg ml with respect to biofilm formation and preformed biofilms, respectively. SEM micrographs of S. mutans treated with [W]KR12-KAEK suggested damage to the bacterial surface. [W]KR12-KAEK is demonstrated to be an antimicrobial agent to control microbial biofilms.

This study evaluated the antibacterial, antifungal, and antioxidant effect of 7-hydroxy-4',6dimethoxy-isoflavone and essential oil of Myroxylon peruiferum. The compound was isolated and its structure elucidated by NMR. The chemical composition of essential oil determined by gC-MS analysis. To evaluation of antimicrobial activity, the Minimum Inhibitory Concentration (MIC), Minimum Bactericidal Concentration (MBC) and Minimum Fungicidal Concentration (MFC) were performed. In addition to analysis of antioxidant activity, DPPH radical scavenging tests, iron chelating assay (FIC), antioxidant reducing power assay (FRAP) and β-carotene bleaching assay (BCB) were performed. For the essential oil were identified 24 organized compounds having as main constituents; Germacrene D (17.2%), α-pinene (14.8%) and E-caryophyllene (10.8%). The results showed that isoflavone (2000 to 156 μg/mL) and essential oil (5.0 to 1.25%) present antibacterial and antifungal activity against Gram-positive bacteria and filamentous fungi. The isoflavone and the essential oil also presented antioxidant activity in all the tests, mainly on inhibition of the oxidation of β-carotene test concentrations ranging from 60 to 100%. In conclusion, isoflavone and essential oil from M. peruiferum present an antimicrobial alternative against gram-positive bacteria, especially of the genus Staphylococcus and dermatophyte fungi of the genus Trichophyton, as well as a natural compound antioxidant.

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