Antimicrobial activity and chemical analyses of seven Juniperus L. species

The objective of this study was to present a comparative analysis of the antimicrobial activity of methanolic leaf extracts from seven Juniperus L. species, together with a tentative analysis of their total flavonoid and o-dihydroxyphenolic acids content. The chemical analyses were performed by colorimetric methods and the antimicrobial activity was assessed via broth microdilution. The studied extracts showed total content of o-dihydroxyphenols in the range of 26 to 34 µg of caffeic acid equivalent/mg DE and total flavonoid content of 13 to 24 µg of quercetin equivalent/mg DE. The sensitivity of Gram-positive bacteria to the studied extracts differed significantly with the following order of activity: J. sabina var. balkanensis > J. communis ‘Laxa’ > J. formosana > J. pinchotii > J. ashei > J. excelsa ≈ J. sibirica. Weak activity was observed for all extracts against Gram-negative bacteria and Candida strains. The analysis of the MBC/MIC ratio showed that the extracts exhibited bactericidal effect against Gram-negative bacteria (MBC/MIC≤4), while bactericidal or bacteriostatic action (MBC/MIC>4) was determined towards Gram-positive bacteria. Moreover, these extracts showed fungicidal (MFC/MIC≤4) or fungistatic effect (MFC/MIC>4). Best antibacterial activity was registered for the J. sabina var. balkanensis leaf extract. The multivariate data analyses were carried out by SIMCA 16 (v16.0.2) software. The hierarchical cluster analysis and principal component analysis, based on phytochemical and antimicrobial data, classified the studied juniper species into four groups: 1. J. ashei; 2. J. excelsa, J. sibirica; 3. J. sabina var. balkanensis, J. communis Laxa, J. formosana; 4. J. pinchotii.