Abstract
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.
Highlights
Antibiotic resistance has drawn the attention of public agencies all over the world
The extracts and some isolated compounds were evaluated for their antibiotic activity against Gram-positive bacteria S. aureus (NEWP0023 and clinical strain resistant to clindamycin, erythromycin and penicillin G), E. faecalis (NEWP0012) and E. faecium and Gramnegative Escherichia coli (NEWP0022) by the broth microdilution assay (Honda et al 2016a)
Among the 12 assessed extracts, the antimicrobial activity of 9 of them is being described for the first time
Summary
Antibiotic resistance has drawn the attention of public agencies all over the world. According to Rai et al (2017) there are about 2 million cases of resistant infections per year in the United States, with 23,000 deaths, and in Europe, the death toll reaches 25,000 per annum. The situation in Asia and developing countries is even more worrying and considering the increase in antibiotic resistance to several pathogens, infections with multi-resistant microorganisms are estimated to account for 10 million deaths per year by. 2050, surpassing other diseases such as cancer (Rai et al 2017). Taking this into account, the search for new active compounds should be frequent to keep up with the adaptability of bacteria. Processes in drug discovery, activity optimization and characterization of selectivity and toxicity of compounds are of utmost importance
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