Antimicrobial resistance (AMR) is a global public health problem, and the rapid rise in AMR is attributed to the inappropriate and/or overuse of antibiotics. Therefore, alternative antimicrobial agents, including those of natural origin, are being sought for the development of new drugs. The purpose of our study was to analyze the chemical composition, and antimicrobial and antioxidant activities of four oregano essential oils (OEOs) from Poland, Europe, Turkey and the USA. The antimicrobial activity (AMA) was evaluated using 23 strains, including Gram-positive bacteria, Gram-negative bacteria and Candida species. The antioxidant activity (AA) of essential oils (EOs) was determined by the DPPH method. The main component of the EOs tested was carvacrol (76.64–85.70%). The highest amount of this compound was determined in the Polish OEO. The OEOs we tested showed antimicrobial resistance, which was especially strong against fungi (MIC = 0.06–0.25 mg/mL⁻¹). These products also showed high AA (71.42–80.44%). OEOs high in carvacrol should be the subject of further research as potential antimicrobial and antioxidant agents.

The antimicrobial properties of essential oil from Lavandula sp. raise hopes related to its use in phytotherapy. This study aimed to evaluate the antimicrobial activity of essential oils from cultivars of L. angustifolia (‘Hidcote Blue Strain’, ‘Hidcote Blue’) and L. × intermedia (‘Phenomenal’, ‘Grosso’) grown in central-eastern Poland, that is, at the border of the northern lavender cultivation range. The chemical composition of the essential oils was determined by GC/MS. Essential oil concentrations (20, 10, 5, 2.5, 1.25, 0.6, 0.3, 0.16, 0.08, and 0.04 mg/mL) were tested to determine the minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) or minimum fungicidal concentration (MFC) towards ten strains of Gram-positive bacteria, five Gram-negative bacteria, and eight yeasts in vitro culture. Essential oils from the Lavendula cultivars showed antimicrobial activity against all microorganisms analysed. The yeasts were characterised by higher sensitivity to lavender oil compared to bacteria, while Gram-positive bacteria were more sensitive than Gram-negative bacteria. The lowest MIC values for bacteria and fungi were obtained for ‘Grosso’. Furthermore, the ‘Grosso’ oil showed the highest fungicidal activity, while the highest bactericidal activity was found in ‘Hidcote Blue’ and ‘Grosso’. Using Staphylococcus aureus as an example, it was shown that different bacterial strains of the same species show varying sensitivity to the essential oil. A higher oil content was noted for the cultivars L. × intermedia, especially for the ‘Phenomenal’. Linalyl acetate and linalool were the main components of the essential oil in all cultivars. However, in the ‘Grosso’ oil, a high content of terpinen-4-ol (18.08%) was also recorded. An analysis of the relationships between the content of the main components in the analysed essential oils and the antimicrobial activity of essential oils suggested that linalool and terpinen-4-ol were compounds potentially responsible for antimicrobial activity. The obtained results allow us to conclude that essential oil with significant antimicrobial activity can be obtained from Lavandula sp. plants harvested in the northern part of the cultivation range.

Extracts from the June collection of aerial parts of Helianthus salicifolius A. Dietr and Helianthus tuberosus L. were obtained using carbon dioxide supercritical fluid extraction with water as co-solvent. The antimicrobial effect in vitro of these extracts was then determined against reference species of bacteria, as well as against fungi (represented by Candida spp.). Both extracts were found to possess antimicrobial activity, with MIC = 0.62–5 mg mL⁻¹ for bacteria and MIC = 5–10 mg mL⁻¹ for yeasts, and both extracts demonstrated suitable bactericidal and fungicidal effect. The highest activity was observed against S. aureus ATCC 29213 (MIC = 0.62 mg mL⁻¹ for H. salicifolius extract; MIC = 2.5 mg mL⁻¹ for H. tuberosus extract) as confirmed by time–kill assay. Higher antioxidant activity was found for H. tuberosus extract (EC₅₀ = 0.332 mg mL⁻¹) as compared to that of H. salicifolius (EC₅₀ = 0.609 mg mL⁻¹). The total polyphenol content (TPC) expressed as gallic acid equivalents (GAE) was 13.75 ± 0.50 mg GAE g⁻¹ of H. salicifolius extract and 33.06 ± 0.80 mg GAE g⁻¹ of H. tuberosus extract. There was a relationship between the antioxidant potential of both extracts and TPC, but not between antistaphylococcal activity and TPC. The ATIR–FTIR spectra of both extracts showed similar main vibrations of the functional groups typical for phytoconstituents possessing bioactivity. The obtained data suggest potential application of these extracts as natural antioxidants and preparations with biocidal activity. Additionally, both extracts may be regarded as potential natural conservants in cosmetics, as well as natural preservatives in food.

Beta vulgaris L. is an edible plant with health-beneficial activities. The profile of betaxanthins is more complex than previously described in beetroot cultivars. Twenty-four betaxanthins were detected in extracts of the peel and flesh of five cultivars by HPLC-DAD-ESI-MS, of which two new betaxanthins (arginine-Bx and ornithine-Bx) were detected for the first time in B. vulgaris cultivars. The content of betaxanthins in the studied cultivars decreased in the Tytus > Ceryl > Chrobry > Forono > Boldor sequence. The highest content of compounds (1231 mg/100 g DE) was observed in the Tytus cultivar (peel). The peel of B. vulgaris, which is often considered a waste, appeared to be a richer source of betaxanthins compared to its flesh. Antibacterial and antifungal activities were determined against twenty-three microorganisms. Tytus (peel) showed a moderate or good bactericidal effect, especially against the majority of Gram-positive bacteria as well as against most of the tested fungi (MIC = 0.125–0.5 mg/mL) and additionally characterized by low cytotoxicity towards non-cancerous cells (CC₅₀ = 405 μg/mL, CC₅₀—50% cytotoxic concentration). Tytus flesh also showed a high cytotoxicity value against human cervical adenocarcinoma (HeLa), with CC₅₀ of 282 μg/mL. Correlation analysis was used to determine the relationship between the betaxanthin profiles and antimicrobial and anticancer activities. Arginine-Bx, proline-Bx, and tryptophan-Bx were indicated as active against HeLa and the colon cancer cell line (RKO), while asparagine-Bx and phenylalanine-Bx was responsible for activity against all tested bacterial and yeast species. The significant effectiveness and safety of these beetroots make indicated compounds promising applicants as antimicrobial and anticancer agents.

Curcuma longa from Zingiberaceae belongs to the major spices consumed around the world, known from its cholagogue, anti-inflammatory, and antimicrobial properties. Lack of data on the activity of single components of turmeric extract encouraged the authors to apply TLC (thin-layer chromatography) based bioautography studies to reveal its antimicrobial constituents and construct a universal platform for the bioactivity assessment of crude extracts, with help of a freeware ImageJ software. This optimized chromatographic bioassay performed on diethyl ether and methanol extracts of Curcuma longa was successfully applied on the total extract and revealed the antimicrobial potential of single components against a variety of Gram-positive strains, with no need for their isolation from the mixture. The obtained results were further confronted with a classic microdilution antimicrobial assay on the isolates, purified from the crude extracts by centrifugal partition chromatography in the following solvent system: heptane-chloroform-methanol-water (5:6:3:2) (v/v/v/v).

Numerous species of Allium genus have been used in the traditional medicine based on their vast biological effects, e.g., antimicrobial, digestion stimulant, anti-sclerotic, soothing, antiradical or wound healing properties. In this work, unpolar and polar extracts from two lesser-investigated species of Allium growing in Kazakhstan, Alliumgalanthum Kar. & Kir. (AG) and A. turkestanicum Regel. (AT), were studied for their composition and biological effects. In the HPLC-ESI-QTOF-MS/MS analyses of water and alcoholic extracts simple organic acids, flavonoids and their glycosides were found to be the best represented group of secondary metabolites. On the other hand, in the GC-MS analysis diethyl ether, extracts were found to be rich sources of straight-chain hydrocarbons and their alcohols, fatty acids and sterols. The antimicrobial activity assessment showed a lower activity of polar extracts, however, the diethyl ether extract from AT bulbs and AG chives showed the strongest activity against Bacillus subtilis ATCC 6633, B. cereus ATCC 10876, some species of Staphylococcus (S. aureus ATCC 25923 and S. epidermidis ATCC 12228) and all tested Candida species (Candida albicans ATCC 2091, Candida albicans ATCC 10231, Candida glabrata ATCC 90030, Candida krusei ATCC 14243 and Candida parapsilosis ATCC 22019) with a minimum inhibitory concentration of 0.125–0.5 mg/mL. The highest antiradical capacity exhibited diethyl ether extracts from AG bulbs (IC50 = 19274.78 ± 92.11 mg Trolox eq/g of dried extract) in DPPH assay. In ABTS scavenging assay, the highest value of mg Trolox equivalents, 50.85 ± 2.90 was calculated for diethyl ether extract from AT bulbs. The same extract showed the highest inhibition of mushroom tyrosinase (82.65 ± 1.28% of enzyme activity), whereas AG bulb ether extract was the most efficient murine tyrosinase inhibitor (54% of the enzyme activity). The performed tests confirm possible cosmeceutical applications of these plants.