Herbal medicine requires searching for new sources with antimicrobial activity. Alkanna sp. (Boraginaceae) is widely used in medicine due to detoxification and antibacterial effects. The aim of this study was to obtain Alkanna orientalis (L.) Boiss. plant callus extracts, to investigate antimicrobial activity of extracts against bacteria and yeast and to reveal responsible mechanisms. Callus tissue cultures have been obtained using different nutrient media. Antimicrobial activity and minimal inhibitory concentrations (MIC) were determined by the methods of extract diffusion in agar and dilution using different test-microorganisms. Quantity and quality of naphthoquinones were determined using spectrophotometric and high performance liquid chromatographic analyses. H+/K+ exchange by whole cells was assayed using selective electrodes, ATPase activity and SH-groups number of membrane vesicles—by spectrophotometric methods. It was revealed that callus extracts containing naphthoquinones (0.19 ± 0.01 %) possessed bacteriostatic activity against gram-positive bacteria including pathogenic ones (MIC were 125–750 μg/mL−1), and bactericidal activity against lactic acid bacteria (Lactobacillus acidophilus, L. rhamnosus) (MIC was 250 μg/mL). MIC against Enterococcus hirae was 250 μg/mL of callus extract or 31.25 μg/mL of shikonin. It depended on the medium content, cultivation duration and the activity remained for 10–11 years. Moreover, intact root extracts inhibited H+/K+ exchange of E. hirae but callus extracts had a stronger effect. The inhibitor, N,N′-dicyclohexylcarbodiimide (DCCD)-sensitive H+/K+ exchange was changed; ATPase activity and SH-groups number were lowered by two and more fold under the influence of the extracts. Alkanet root and callus tissues extracts were concluded to have a high antimicrobial activity. So, they might directly affect the FOF1-ATPase which in turn regulates the bacterial growth. These results are useful for further investigation of alkanet extracts composition and their application as an alternative antimicrobial agent in pharmaceutical and food industry as well as in medicine.
