Screening of some medicinal plants from cameroon forβ-Lactamase inhibitory activity

Acorus calamus L. rhizome extract and its bioactive fraction exhibits antibacterial effect by modulating membrane permeability and fatty acid composition

ETHNOPHARMACOLOGICAL RELEVANCE

India's ancient texts, the Charak Samhita and Sushruta Samhita, make reference to the traditional medicinal usage of Acorus calamus L. In India and China, it has long been used to cure stomach aches, cuts, diarrhea, and skin conditions. This ability of the rhizome is attributed to its antimicrobial properties. Research studies to date have shown its antimicrobial properties. However, scientific evidence on its mode of action is still lacking.

AIM OF THE STUDY

Acorus calamus L. rhizome extract and its bioactive fraction exhibits antibacterial effect by modulating membrane permeability and fatty acid composition.

MATERIAL AND METHOD

The secondary metabolites in the rhizome of A. calamus L. were extracted in hexane using Soxhlet apparatus. The ability of the extract to inhibit multidrug resistant bacterial isolates, namely Bacillus cereus, Escherichia coli, Acinetobacter baumannii, and Pseudomonas aeruginosa were evaluated using checkerboard assay. Further, the extract was purified using thin layer chromatography, gravity column chromatography, and combiflash chromatography. Structure elucidation of the active compound was done using GC-MS, FT-IR, and UV-Vis spectral scan. The mode of action of the bioactive fraction was determined. Bacterial membrane damage was analyzed using SEM, membrane permeability was determined using SYBR green I and PI dye, leakage of cytoplasmic contents were analyzed using Bradford assay and Fehling's reagent. The ability to inhibit efflux pump of A. baumannii was determined using EtBr accumulation assay and β-lactamase inhibition was analyzed using nitrocefin as substrate. Also, the biofilm inhibition of B. cereus was determined using crystal violet dye. Moreover, the effect of the bioactive fraction on the fatty acid profile of the bacterial membrane was determined by GC-FAME analysis using 37 component FAME mix as standard.

RESULTS

Acorus calamus L. rhizome hexane extract (AC-R-H) demonstrated broad-spectrum antibacterial activity against all the isolates tested. AC-R-H extract also significantly reduced the MIC of ampicillin against all tested bacteria, indicating its bacterial resistance modulating properties. The assay guided purification determined Asarone as the major compound present in the bioactive fraction (S-III-BAF). S-III-BAF was found to reduce the MIC of ampicillin against Escherichia coli (100-25 mg/mL), Pseudomonas aeruginosa (15-3.25 mg/mL), Acinetobacter baumannii (12.5-1.56 mg/ml), and Bacillus cereus (10-1.25 mg/mL). Further, it recorded synergistic activity with ampicillin against B. cereus (FICI = 0.365), P. aeruginosa (FICI = 0.456), and A. baumannii (FICI = 0.245). The mode of action of S-III-BAF can be attributed to its ability to disturb the membrane integrity, enhance membrane permeability, reduce biofilm formation, and possibly alter the fatty acid composition of the bacterial cell membranes.

CONCLUSION

The bioactive fraction of AC-R-H extract containing Asarone as the active compound showed antibacterial activity and synergistic interactions with ampicillin against the tested bacterial isolates. Such activity can be attributed to the modulation of fatty acids present in bacterial membranes, which enhances membrane permeability and causes membrane damage.

In vitro and computational studies of the β-lactamase inhibition and β-lactam potentiating properties of plant secondary metabolites

β-lactam resistance in bacteria is primarily mediated through the production of β-lactamases. Among the several strategies explored to mitigate the issue of β-lactam resistance, the use of plant secondary metabolites in combination with existing β-lactams seem promising. The present study aims to identify possible β-lactam potentiating plant secondary metabolites following in vitro and in silico approaches. Among 180 extracts from selected 30 medicinal plants, acetone extract of Ficus religiosa (FRAE) bark recorded the least IC50 value of 3.9 mg/ml. Under in vitro conditions, FRAE potentiated the activity of ampicillin, which was evidenced by the significant reduction in IC50 values of ampicillin against multidrug resistant bacteria. Metabolic profiling following HR-LCMS analysis revealed the presence of diverse metabolites viz. flavonoids, alkaloids, terpenoids, etc. in FRAE. Further, ensemble docking of the FRAE metabolites against four Class A β-lactamase (SHV1, TEM1, KPC2 and CTX-M-27) showed quercetin, taxifolin, myricetin, luteolin, and miquelianin as potential inhibitors with the least average binding energy. In molecular dynamic simulation studies, myricetin formed the most stable complex with SHV1 and KPC-2 while miquelianin with TEM1 and CTX-M-27. Further, all five metabolites interacted with amino acid residue Glu166 in Ω loop of β-lactamase, interfering with the deacylation step, thereby disrupting the enzyme activity. The pharmacokinetics and ADMET profile indicate their drug-likeness and non-toxic nature, making them ideal β-lactam potentiators. This study highlights the ability of metabolites present in FRAE to act as β-lactamase inhibitors.Communicated by Ramaswamy H. Sarma.

The African cherry: A review of the botany, traditional uses, phytochemistry, and biological activities of Prunus africana (Hook.f.) Kalkman

ETHNOPHARMACOLOGICAL RELEVANCE

Prunus africana (Hook.f.) Kalkman (Rosaceae), commonly known as "Pygeum" or "African cherry", occurs in mainland montane forests scattered across sub-Saharan Africa, Madagascar, and some surrounding islands. Traditionally, decoctions of the stem-bark are taken orally for the treatment of a wide variety of conditions, such as benign prostatic hyperplasia (BPH), stomach ache, chest pain, malaria, heart conditions, and gonorrhoea, as well as urinary and kidney diseases. The timber is used to make axe handles and for other household needs. The dense wood is also sawn for timber.

AIM

The fragmented information available on the ethnobotany, phytochemistry, and biological activities of the medicinally important P. africana was collated, organised, and analysed in this review, to highlight knowledge voids that can be addressed through future research.

MATERIALS AND METHODS

A bibliometric analysis of research output on P. africana was conducted on literature retrieved, using the Scopus® database. The trend in the publications over time was assessed and a network analysis of collaborations between countries and authors was carried out. Furthermore, a detailed review of the literature over the period 1971 to 2021, acquired through Scopus, ScienceDirect, SciFinder, Pubmed, Scirp, DOAJ and Google Scholar, was conducted. All relevant abstracts, full-text articles and various book chapters on the botanical and ethnopharmacological aspects of P. africana, written in English and German, were consulted.

RESULTS

A total of 455 documents published from 1971 to 2021, were retrieved using the Scopus search. Analysis of the data showed that the majority of these documents were original research articles, followed by reviews and lastly a miscellaneous group comprising conference papers, book chapters, short surveys, editorials and letters. Data were analysed for annual output and areas of intense research focus, and countries with high research output, productive institutions and authors, and collaborative networks were identified. Prunus africana is reported to exhibit anti-inflammatory, analgesic, antimicrobial, anti-oxidant, antiviral, antimutagenic, anti-asthmatic, anti-androgenic, antiproliferative and apoptotic activities amongst others. Phytosterols and other secondary metabolites such as phenols, triterpenes, fatty acids, and linear alcohols have been the focus of phytochemical investigations. The biological activity has largely been ascribed to the phytosterols (mainly 3-β-sitosterol, 3-β-sitostenone, and 3-β-sitosterol-glucoside), which inhibit the production of prostaglandins in the prostate, thereby suppressing the inflammatory symptoms associated with BPH and chronic prostatitis.

CONCLUSIONS

Many of the ethnobotanical assertions for the biological activity of P. africana have been confirmed through in vitro and in vivo studies. However, a disparity exists between the biological activity of the whole extract and that of single compounds isolated from the extract, which were reported to be less effective. This finding suggests that a different approach to biological activity studies should be encouraged that takes all secondary metabolites present into consideration. A robust technique, such as multivariate biochemometric data analysis, which allows for a holistic intervention to study the biological activity of a species is suggested. Furthermore, there is a need to develop rapid and efficient quality control methods for both raw materials and products to replace the time-consuming and laborious methods currently in use.

In Vitro Phytotherapeutic Properties of Aqueous Extracted Adenia viridiflora Craib. towards Civilization Diseases

Adenia viridiflora Craib. is an indigenous edible plant that became an endangered species due to limited consumption of the local population with unknown reproduction and growth conditions. The plant is used as a traditional herb; however, its health applications lack scientific-based evidence. A. viridiflora Craib. plant parts (old leaves and young shoots) from four areas as Kamphaeng Phet (KP), Muang Nakhon Ratchasima (MN), Pakchong Nakhon Ratchasima (PN), and Uthai Thani (UT) origins were investigated for phenolic compositions and in vitro health properties through the inhibition of key enzymes relevant to obesity (lipase), diabetes (α-glucosidase and dipeptidyl peptidase-IV), Alzheimer’s disease (cholinesterases and β-secretase), and hypertension (angiotensin-converting enzyme). Phenolics including p-coumaric acid, sinapic acid, naringenin, and apigenin were detected in old leaves and young shoots in all plant origins. Old leaves exhibited higher total phenolic contents (TPCs) and total flavonoid contents (TFCs), leading to higher enzyme inhibitory activities than young shoots. Besides, PN and MN with higher TPCs and TFCs tended to exhibit greater enzyme inhibitory activities than others. These results will be useful to promote this plant as a healthy food with valuable medicinal capacities to support its consumption and agricultural stimulation, leading to sustainable conservation of this endangered species.

Plant-Based Phytochemicals as Possible Alternative to Antibiotics in Combating Bacterial Drug Resistance

The unprecedented use of antibiotics that led to development of resistance affect human health worldwide. Prescription of antibiotics imprudently and irrationally in different diseases progressed with the acquisition and as such development of antibiotic resistant microbes that led to the resurgence of pathogenic strains harboring enhanced armors against existing therapeutics. Compromised the treatment regime of a broad range of antibiotics, rise in resistance has threatened human health and increased the treatment cost of diseases. Diverse on metabolic, genetic and physiological fronts, rapid progression of resistant microbes and the lack of a strategic management plan have led researchers to consider plant-derived substances (PDS) as alternative or in complementing antibiotics against the diseases. Considering the quantitative characteristics of plant constituents that attribute health beneficial effects, analytical procedures for their isolation, characterization and phytochemical testing for elucidating ethnopharmacological effects has being worked out for employment in the treatment of different diseases. With an immense potential to combat bacterial infections, PDSs such as polyphenols, alkaloids and tannins, present a great potential for use, either as antimicrobials or as antibiotic resistance modifiers. The present study focuses on the mechanisms by which PDSs help overcome the surge in resistance, approaches for screening different phytochemicals, methods employed in the identification of bioactive components and their testing and strategies that could be adopted for counteracting the lethal consequences of multidrug resistance.

Bioassay Guided Isolation and Docking Studies of a Potential β-Lactamase Inhibitor from Clutia myricoides

Infectious diseases are the second major cause of death worldwide, and the ability to resist multiple classes of antibiotics is the key factor in enabling pathogenic organisms to survive and spread in the nosocomial environment. Unfortunately, the available β-lactamase inhibitors are not efficient against β-lactamase B, C, and D which necessitates discovering either broad spectrum β-lactamase inhibitors or new β-lactam antibiotics resistant to bacterial enzymes. In this regard, products of natural origin have prompted the disclosure of new compounds and medicinal leads. Chloroform fraction of Clutia myricoides (Soa’bor) showed a pronounced activity against extended-spectrum β-lactamase (ESBL) strains. Bio-guided fractionation resulted in isolation of two new compounds; 2-methoxy chrysophanol (2) and Saudin-I (5) in addition to three known compounds that were identified as chrysophanol (1), stigmasterol (3) and β-sitosterol (4). Antibacterial and anti ESBL activities of the isolated compounds were performed. No antibacterial activities were detected for any of the tested compounds. Meanwhile, compound 2 showed promising anti ESBL activity. Compound 2 has shown an obvious activity against K. pneumoniae ATCC 700603 with a marked enlargement of inhibition zones (>5mm) in combination with third generation cephalosporin antibiotics. To further understand the mechanism of action of compound 2, molecular docking was carried out against CTX-M-27 ESBL. The results showed binding site interactions strikingly different from its analogue, compound 1, allowing compound 2 to be active against ESBL. These results proposed the concomitant use of these active compounds with antibiotics that would increase their efficiency. Nevertheless, the interaction between this active compound and antibiotics should be taken into consideration. Therefore, in order to evaluate the safety of this active compound, further in vitro and in vivo toxicity assays must be carried out.

Strategies for discovery of new molecular targets for anti-infective drugs

Multidrug resistant bacterial pathogens as causative agents of infectious disease are a primary public health concern. Clinical efficacy of antimicrobial chemotherapy toward bacterial infection has been compromised in cases where causative agents are resistant to multiple structurally distinct antimicrobial agents. Modification of extant antimicrobial agents that exploit conventional bacterial targets have been developed since the advent of the antimicrobial era. This approach, while successful in certain cases, nonetheless suffers overall from the costs of development and rapid emergence of bacterial variants with confounding resistances to modified agents. Thus, additional strategies toward discovery of new molecular targets have been developed based on bioinformatics analyses and comparative genomics. These and other strategies meant to identify new molecular targets represent promising avenues for reducing emergence of bacterial infections. This short review considers these strategies for discovery of new molecular targets within bacterial pathogens.

Role of Natural Product in Modulation of Drug Transporters and New Delhi Metallo-β Lactamases

A rapid growth in drug resistance has brought options for treating antimicrobial resistance to a halt. Bacteria have evolved to accumulate a multitude of genes that encode resistance for a single drug within a single cell. Alternations of drug transporters are one of the causes for the development of resistance in drug interactions. Conversely, the production of enzymes also inactivates most antibiotics. The discovery of newer classes of antibiotics and drugs from natural products is urgently needed. Alternative medicines play an integral role in countries across the globe but many require validation for treatment strategies. It is essential to explore this chemical diversity in order to find novel drugs with specific activities which can be used as alternative drug targets. This review describes the interaction of drugs with resistant pathogens with a special focus on natural product-derived efflux pump and carbapenemase inhibitors.

Ethnopharmacology and Therapeutic Value of Bridelia micrantha (Hochst.) Baill. in Tropical Africa: A Comprehensive Review

Bridelia micrantha is traditionally used in tropical Africa to treat a wide range of human and animal diseases. The aim of this study was to summarise the research that has been done on the ethnomedicinal uses, phytochemistry and pharmacological properties of B. micrantha so as to understand its importance and potential value in primary healthcare systems. The literature search for information on ethnomedicinal uses and pharmacological activities of B. micrantha was undertaken using databases such as Web of Science, Scopus, Google Scholar, Science Direct, BioMed Central (BMC), PubMed and Springerlink. Other relevant literature sources included books, book chapters, websites, theses, conference papers and other scientific publications. This study showed that B. micrantha is used as herbal medicine in just over half (57.3%) of the countries in tropical Africa where it is indigenous. A total of 54 ethnomedicinal uses of B. micrantha have been recorded with a high degree of consensus on burns, wounds, conjunctivitis, painful eyes, constipation, gastric ulcers, cough, headache, rheumatism, painful joints, dysentery, ethnoveterinary medicine, malaria, sexually transmitted infections, stomach ache, tape worms and diarrhoea. Different plant parts, aqueous and organic extracts exhibited anthelmintic, antimicrobial, anticonvulsant and sedative, antidiabetic, antidiarrhoeal, antinociceptive, antioxidant, antiplasmodial, antischistosomal, hepatoprotective, insecticidal and β-lactamase inhibitory activities.

Characterization of a potential β-lactamase inhibitory metabolite from a marine Streptomyces sp. PM49 active against multidrug-resistant pathogens

Actinobacteria is a prolific producer of complex natural products; we isolated a potential marine Streptomyces sp. PM49 strain from Bay of Bengal coastal area of India. The strain PM49 exhibited highly efficient antibacterial properties on multidrug-resistant pathogens with a zone of inhibition of 14-17 mm. SSF was adopted for the production of the secondary metabolites from PM49 with ISP2; utilizing agricultural wastes for compound extraction was also attempted. Bioactive fraction of Rf value 0.69 resolved using chloroform and ethyl acetate (1:1, v/v) was obtained and subjected to further analysis. Based on UV, IR, ESI-MS, and (1)H and (13)C NMR spectral analysis, it was revealed that the compound is closely similar to cyslabdan with a molecular mass of 467.66 corresponding to the molecular formula C25H41NO5S. ESBL and MBL production was screened in the hospital test isolates of Pseudomonas aeruginosa, Acinetobacter baumannii, Klebsiella pneumoniae, and Staphylococcus aureus. PCR amplification in the phenotypically positive strains was positive for bla IMP, bla SHV, bla CTX-M, and mec genes. The β-lactamase enzyme from tested strains had cephalosporinase activity with a 31-kDa protein and isolated compound from the strain possessing β-lactamase inhibitory potential. MIC of the active fraction was 16-32 μg/ml on ATCC strains; the ceftazidime and meropenem sensitive and resistant test strains showed MIC of 64-256 μg/ml. The Streptomyces sp. PM49 aerial mycelium was rectiflexibile; the 16S rRNA showed 99 % identity with Streptomyces rochei and submitted at Genbank with accession no JX904061.1.

Combating pathogenic microorganisms using plant-derived antimicrobials: a minireview of the mechanistic basis

The emergence of antibiotic resistance in pathogenic bacteria has led to renewed interest in exploring the potential of plant-derived antimicrobials (PDAs) as an alternative therapeutic strategy to combat microbial infections. Historically, plant extracts have been used as a safe, effective, and natural remedy for ailments and diseases in traditional medicine. Extensive research in the last two decades has identified a plethora of PDAs with a wide spectrum of activity against a variety of fungal and bacterial pathogens causing infections in humans and animals. Active components of many plant extracts have been characterized and are commercially available; however, research delineating the mechanistic basis of their antimicrobial action is scanty. This review highlights the potential of various plant-derived compounds to control pathogenic bacteria, especially the diverse effects exerted by plant compounds on various virulence factors that are critical for pathogenicity inside the host. In addition, the potential effect of PDAs on gut microbiota is discussed.

Phytochemical and biological studies of Ochna species

The genus Ochna L. (Gr, Ochne; wild pear), belonging to the Ochnaceae family, includes ca. 85 species of evergreen trees, shrubs, and shrublets, distributed in tropical Asia, Africa, and America. Several members of this genus have long been used in folk medicine for treatment of various ailments, such as asthma, dysentery, epilepsy, gastric disorders, menstrual complaints, lumbago, ulcers, as an abortifacient, and as antidote against snake bites. Up to now, ca. 111 constituents, viz. flavonoids (including bi-, tri-, and pentaflavonoids), anthranoids, triterpenes, steroids, fatty acids, and a few others have been identified in the genus. Crude extracts and isolated compounds have been found to exhibit analgesic, anti-HIV-1, anti-inflammatory, antimalarial, antimicrobial, and cytotoxic activities, lending support to the rationale behind several of its traditional uses. The present review compiles the informations concerning the traditional uses, phytochemistry, and biological activities of Ochna.

Current challenges in antimicrobial chemotherapy: focus on ß-lactamase inhibition

The use of the three classical beta-lactamase inhibitors (clavulanic acid, tazobactam and sulbactam) in combination with beta-lactam antibacterials is currently the most successful strategy to combat beta-lactamase-mediated resistance. However, these inhibitors are efficient in inactivating only class A beta-lactamases and the efficiency of the inhibitor/antibacterial combination can be compromised by several mechanisms, such as the production of naturally resistant class B or class D enzymes, the hyperproduction of AmpC or even the production of evolved inhibitor-resistant class A enzymes. Thus, there is an urgent need for the development of novel inhibitors. For serine active enzymes (classes A, C and D), derivatives of the beta-lactam ring such as 6-beta-halogenopenicillanates, beta-lactam sulfones, penems and oxapenems, monobactams or trinems seem to be potential starting points to design efficient molecules (such as AM-112 and LK-157). Moreover, a promising non-beta-lactam molecule, NXL-104, is now under clinical development. In contrast, an ideal inhibitor of metallo-beta-lactamases (class B) remains to be found, despite the huge number of potential molecules already described (biphenyl tetrazoles, cysteinyl peptides, mercaptocarboxylates, succinic acid derivatives, etc.). The search for such an inhibitor is complicated by the absence of a covalent intermediate in their catalytic mechanisms and the fact that beta-lactam derivatives often behave as substrates rather than as inhibitors. Currently, the most promising broad-spectrum inhibitors of class B enzymes are molecules presenting chelating groups (thiols, carboxylates, etc.) combined with an aromatic group. This review describes all the types of molecules already tested as potential beta-lactamase inhibitors and thus constitutes an update of the current status in beta-lactamase inhibitor discovery.