Abstract
Two Balkan Peninsula endemics, Nepeta rtanjensis and N. argolica subsp. argolica, both characterized by specialized metabolite profiles predominated by iridoids and phenolics, are differentiated according to the stereochemistry of major iridoid aglycone nepetalactone (NL). For the first time, the present study provides a comparative analysis of antimicrobial and immunomodulating activities of the two Nepeta species and their major iridoids isolated from natural sources—cis,trans-NL, trans,cis-NL, and 1,5,9-epideoxyloganic acid (1,5,9-eDLA), as well as of phenolic acid rosmarinic acid (RA). Methanol extracts and pure iridoids displayed excellent antimicrobial activity against eight strains of bacteria and seven strains of fungi. They were especially potent against food-borne pathogens such as L. monocytogenes, E. coli, S. aureus, Penicillium sp., and Aspergillus sp. Targeted iridoids were efficient agents in preventing biofilm formation of resistant P. aeruginosa strain, and they displayed additive antimicrobial interaction. Iridoids are, to a great extent, responsible for the prominent antimicrobial activities of the two Nepeta species, although are probably minor contributors to the moderate immunomodulatory effects. The analyzed iridoids and RA, individually or in mixtures, have the potential to be used in the pharmaceutical industry as potent antimicrobials, and in the food industry to increase the shelf life and safety of food products.
Highlights
The plant genus Nepeta L. comprises around 280 species native to Europe, Asia, and Africa, commonly known as catmints or catnips
Nepetalactone is usually present in the form of 7S diastereoisomers, which can be found in species-specific amounts and ratios [1,5]
From natural sources, and to comparatively analyze, for the first time, their antimicrobial activities with those of the crude methanol extracts of the two rare Nepeta species: (1) Nepeta rtanjensis Diklić & Milojević, a critically endangered perennial of Serbia, which is characterized by high amounts of trans,cis-NL, dehydronepetalactone (DNL), and 1,5,9-eDLA, while cis,trans-NL is present as a minor constituent [4,16,17,18]; (2) Greek endemic N. argolica Bory & Chaub. subsp. argolica
Summary
The plant genus Nepeta L. (family Lamiaceae) comprises around 280 species native to Europe, Asia, and Africa, commonly known as catmints or catnips. (family Lamiaceae) comprises around 280 species native to Europe, Asia, and Africa, commonly known as catmints or catnips These remarkable plants are widely used in folk medicine against a variety of diseases and disorders, as well as in traditional food production [1], and their antimicrobial potential against human pathogenic. The present study aimed to isolate trans,cis-NL, cis,trans-NL, and 1,5,9-eDLA from natural sources, and to comparatively analyze, for the first time, their antimicrobial activities with those of the crude methanol extracts of the two rare Nepeta species: (1) Nepeta rtanjensis Diklić & Milojević, a critically endangered perennial of Serbia, which is characterized by high amounts of trans,cis-NL, dehydronepetalactone (DNL), and 1,5,9-eDLA, while cis,trans-NL is present as a minor constituent [4,16,17,18]; (2) Greek endemic N. argolica Bory. Antimicrobial interaction of targeted iridoid compounds and rosmarinic acid (RA) has been investigated within the present study
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