ALBERT

Description: Therapeutic treatment options for opportunistic non-tuberculous mycobacterial (NTM) infection and/or serious mycobacterial infections such as tuberculosis (TB) and leprosy are limited due to the spread of antimicrobial resistance mechanism. Plant-derived natural compounds as prospective efflux pump inhibitors may present a promising adjunct to conventional chemotherapy by enhancing mycobacterial susceptibility to antibiotics. This study served to evaluate the antimicrobial and resistance-modifying profile of a range of plant-derived flavonoids against the mycobacterial model strains: M. smegmatis, M. aurum, and M. bovis BCG. The minimum inhibitory concentrations (MICs) of the compounds against the mycobacterial strains were determined using both agar dilution and broth dilution assays, while their efflux inhibitory activity was investigated via an ethidium bromide-based fluorometric assay. All compounds were screened for their synergistic effects with ethidium bromide (EtBr) and rifampicin (RIF) against M. smegmatis. Skullcapflavone II (5,2′-dihydroxy-6,7,8,6′-tetramethoxyflavone, 1) exerted potent antimicrobial activity against M. aurum and M. bovis BCG and considerably increased the susceptibility of M. smegmatis to EtBr and RIF. Nobiletin (5,6,7,8,3′,4′-hexamethoxyflavone, 2) was determined to be the most potent efflux-inhibitor in M. aurum and M. smegmatis. However, a connection between strong modulatory and putative efflux activity of the compounds could not be observed. Nevertheless, the results highlight two polymethoxyflavones, skullcapflavone II and nobiletin, with potent antimycobacterial and antibiotic resistance modulating activities as valuable adjuvants in anti-mycobacterial therapies.

Description: The culinary herb Satureja montana, known as winter savory, is an ingredient of traditional dishes known in different parts of the world. As an ingredient of foods it has the potential to improve their safety. In this study, the herb’s activity was investigated against Campylobacter jejuni, the leading cause of the most prevalent bacterial gastroenteritis worldwide. The ethanolic extract and essential oil of the herb were chemically characterized and six pure compounds—carvacrol, thymol, thymoquinone, p-cymene, γ-terpinene, and rosmarinic acid—were chosen for further analysis. The antimicrobial activity of the ethanolic extract (MIC 250 mg/L) was 4-fold higher compared to the essential oil. Carvacrol, thymol and thymoquinone had the strongest antimicrobial effect (MIC 31.25 mg/L) and a strong synergistic activity between carvacrol and thymol was determined (FICi 0.2). Strong inhibitory effect on C. jejuni efflux pumps (2-fold inhibition) and disruption of membrane integrity (〉 80% disruption) of the herb were determined as modes of action. For resistance against the herb, C. jejuni need efflux pumps, although increased resistance against this herb does not co-occur with increased efflux pump activity, as for antibiotics. This study shows the potential of a common culinary herb for the reduction of the food pathogen C. jejuni without increasing resistance.

Description: Carvotacetones (1–7) isolated from Sphaeranthus africanus were screened for their antimycobacterial and efflux pump (EP) inhibitory potential against the mycobacterial model strains Mycobacterium smegmatis mc2 155, Mycobacterium aurum ATCC 23366, and Mycobacterium bovis BCG ATCC 35734. The minimum inhibitory concentrations (MICs) of the carvotacetones were detected through high-throughput spot culture growth inhibition (HT-SPOTi) and microbroth dilution assays. In order to assess the potential of the compounds 1 and 6 to accumulate ethidium bromide (EtBr) in M. smegmatis and M. aurum, a microtiter plate-based fluorometric assay was used to determine efflux activity. Compounds 1 and 6 were analyzed for their modulating effects on the MIC of EtBr and the antibiotic rifampicin (RIF) against M. smegmatis. Carvotacetones 1 and 6 had potent antibacterial effects on M. aurum and M. bovis BCG (MIC ≤ 31.25 mg/L) and could successfully enhance EtBr activity against M. smegmatis. Compound 1 appeared as the most efficient agent for impairing the efflux mechanism in M. smegmatis. Both compounds 1 and 6 were highly effective against M. aurum and M. bovis BCG. In particular, compound 1 was identified as a valuable candidate for inhibiting mycobacterial efflux mechanisms and as a promising adjuvant in the therapy of tuberculosis or other non-tubercular mycobacterial infections.

Description: Antibiotic resistance is a growing problem and may become the next major global health crisis if no timely actions are taken. Mycobacterial infections are widespread and, due to antibiotic resistance, also hard to treat and a major cause of mortality. Natural compounds have the potential to increase antibiotic effectiveness due to their resistance modulatory and antimicrobial effects. In this study, Peucedanum ostruthium extracts, fractions, and isolated compounds were investigated regarding their antimicrobial and resistance-modulatory effects as well as efflux pump inhibition in Mycobacterium smegmatis. P. ostruthium extracts were found to have anti-mycobacterial potential and resistance modulating effects on ethidium bromide activity. The major antibacterial effect was attributed to ostruthin, and we found that the more lipophilic the substrate, the greater the antimicrobial effect. Imperatorin caused potent modulatory effects by interfering with the action of the major LfrA efflux pump in M. smegmatis. The plant P. ostruthuim has a complex effect on M. smegmatis, including antibacterial, efflux pump inhibition, resistance modulation, and membrane permeabilization, and its major constituents, ostruthin and imperatorin, have a distinct role in these effects. This makes P. ostruthium and its coumarins promising therapeutics to consider in the fight against drug-resistant mycobacteria.

Description: Reynoutria japonica Houtt. is a critical invasive alien plant in Europe and North America with a drastic impact on native flora. However, R. japonica has medicinal potential, especially as a source of stilbenes. In order to explore the potential of simple extractions of R. japonica, we conducted qualitative and quantitative analyses of fresh R. japonica rhizome infusion, decoction, and macerates with ethanol by UHPLC-DAD-ESI-MSn and UHPLC-DAD, with a focus on major constituent groups of stilbenes and anthranoids. Since R. japonica rhizome extracts showed antimicrobial potential in the past, we also evaluated the antimycobacterial effect of raw R. japonica extracts for the first time against Mycobacterium smegmatis. Of thirty-four characterized substances, six were stilbenes and twelve anthranoids. The main constituents, four trans-stilbenes and eight anthranoids, were quantified in a validated UHPLC-DAD method. The 38% ethanol macerate showed high stilbene (155.078 mg/100 g fluid extract) and low anthranoid content (5.420 mg/100 g fluid extract), while decoction showed the highest anthranoids. Antimycobacterial testing gave good results for all macerates (MIC 256 µg/mL) and trans-resveratrol (64 µg/mL). Extraction and enrichment of stilbenes from fresh plant material by simple extraction methods with food-grade solvents might encourage consideration of wild harvest of rhizomes over classic means of eradication of R. japonica.