Screening of antioxidant and antimicrobial activities on Plectranthus spp. extracts

The use of medicinal plants is a widespread tendency in folk medicine. The Lamiaceae family contains several genera such as sage (Salvia), basil (Ocimum) and mint (Mentha) with a rich diversity of ethnobotanical uses. This study presents the in vitro antibacterial and antioxidant activities evaluation of five species extracts of the Plectranthus genus: P. hadiensis (vr), P. madagascarensis, P. neochilus, P. verticillatus e P. barbatus. Aqueous and acetonic extracts were obtained by five different methods: infusion, decoction, ultrasounds, microwave and maceration (10% w / v of dry plant). The highest amount of dry extract was obtained by the infusion method for Plectranthus barbatus (22,0 ± 1,0 to 33,0 ± 3,0 mg/mL). The extracts obtained were tested for their antimicrobial activity against three Gram-positive bacteria and two Gram-negative bacteria using the well diffusion method. Only the acetonic extracts of P. madagascarensis, P. hadiensis (vd) and P. verticillatus showed antibacterial activity and this was exclusively against Gram-positive bacteria. The highest antimicrobial activity was exhibited by P. madagascarensis extract with inhibition zones ranging from 23 to 36 mm. The antioxidant activity of the extracts was qualitatively determined using the 2,2-diphenyl-l-picrylhydrazyl (DPPH) radical assay in tlc and yielded positive results for the majority of the extracts studied.