Antibacterial potencial of 12 Lichen species.

Resistant bacterial infections are a major public health problem worldwide, which entails the need to search for new therapeutic agents. In this context, lichens stand out, provided that they are producers of structurally diverse compounds that have attractive biological properties, including antimicrobial activity. Thus, extracts of 12 lichen species were prepared and their potential to inhibit the growth of 5 bacterial strains was evaluated in this work. The chemical compositions of these extracts were examined using TLC and microcrystallization, being the identity of the active compounds in each extract attributed based on the bioautography technique. The most active extracts (and their identified active compounds) were from Cladonia borealis (usnic, barbatic and 4-O-demethylbarbatic acids), Cladina confusa (usnic and perlatolic acids), Stereocaulom ramulosum (atranorin, perlatolic and anziaic acids) and Canoparmelia cryptochlorophaea (cryptochlorophaeic and caperatic acids), with MICs ranging from 7.8 to 31.25 µg/mL, including for resistant clinical strains. MIC values ​​were also obtained for substances isolated from lichens for comparison purposes. A group of four extracts containing usnic acid was analyzed by 1H NMR in order to correlate relative proportion of major metabolites and extracts activity. The less active extracts in this group, in fact, presented low proportion of usnic acid.

Antimicrobial potential of Pectis substriata essential oil (Asteraceae) against drug-resistant Staphylococcus strains.

Resistant bacterial infections represent one of the major threats in worldwide health services. In this scenario, plant essential oils are considered promising antimicrobial agents. Therefore, this study aimed to evaluate the antimicrobial potential of Pectis substriata essential oil alone and in combination with antibiotics, against clinical drug-resistant bacterial strains. The essential oil from the plant aerial parts was obtained by hydrodistillation. Antimicrobial activity was assessed against standard and clinical bacterial strains by broth microdilution method, and the synergistic effect was evaluated by checkerboard microtiter assay. The oil alone showed significant activity against clinical Staphylococcus warneri (62.5 µg.mL-1), and was moderately active on Staphylococcus aureus (standard strain) and clinical Staphylococcus intermedius (125 and 250 µg.mL-1, respectively). Synergism was achieved for the combinations of essential oil and ampicillin on S. warneri and of oil and kanamycin on S. intermedius. Additive effects were also observed. This is the first report of the chemical composition of P. substriata essential oil, and the results revealed the presence of compounds with proven antimicrobial activity. The oil proved active against resistant Gram-positive cocci, and showed synergism with antibiotics, revealing its potential use as adjuvant or in the development of new alternative treatments of drug-resistant antimicrobial infections.