Antibacterial and antibiotic-modulation activity of six Cameroonian medicinal plants against Gram-negative multi-drug resistant phenotypes

Antibacterial Activity of Essential Oils Combinations based on Thymus broussonnetii, and Their Synergism with some Antibiotics

The present study aimed to evaluate the antibacterial activity of the essential oil (EO) of Moroccan endemic Thymus broussonnetii alone, and in combination with EOs obtained from selected medicinal plants, namely Myrtus communis, Artemisia herba alba, Thymus pallidus, Thymus satureioides, Teucrium polium, and Rosmarinus officinalis. The synergistic interactions between the most effective combinations based on T. broussonnetii EO with two conventional antibiotics (streptomycin and ciprofloxacin) were also investigated. T. broussonnetii EO possessed a higher inhibitory activity against tested pathogenic bacteria with inhibition zone diameter (IZ) ranging from 21.61 ± 0.03 to 40.09 ± 0.02 mm, and MIC values between 0.140 mg/mL and 0.280 mg/mL. M. communis, A. herba alba, T. pallidus, T. satureioides, T. polium, and R. officinalis EOs showed moderate to weak antibacterial activity. Among tested EO mixtures, the highest synergistic antibacterial effect was recorded with the EO combination of T. broussonnetii and T. pallidus against S. aureus, E. coli, and S. enterica (FICI = 0.258). This EO combination was also the most effective mixture to synergistically enhance the antibacterial activity of the two antibiotics with up to a 128-fold increase, particularly against the gram-negative E. coli. These findings suggest that T. broussonnetii EO may be an interesting source of natural antimicrobials, for use in combination therapies with other plant EOs, and with conventional antimicrobial drugs to tackle the emergence of multidrug-resistant bacteria.

Phytochemical Investigation of Pilea pumila (Clearweed), Laportea canadensis (Wood Nettle), and Boehmeria cylindrica (False Nettle): Three Members of the Urticaceae Family

Phytochemical analysis of 3 members of the Urticaceae family (eg Pilea pumila, Laportea canadensis, and Boehmeria cylindrica) was conducted using GC-MS. P pumila and L canadensis have several recorded historical medicinal uses by Native American tribes, whereas B cylindrica does not. This study was conducted to understand the historical uses in terms of chemical composition. Plant material, separated into aerial or root portions, was dried and extracted using either ethanol or heptane at room temperature. Sterols, fatty acids and esters, terpenes and terpenoids, saturated and monounsaturated hydrocarbons, small oxygen-functionalized organic molecules, and tocopherols were observed using these methods. Plant sterols composed 30.3% to 62.2% of the observed extracts, followed by fatty acids and esters ranging from 0% to 49% and terpenes and terpenoids ranging 4.56% to 33.9%. All 3 plants contained γ-sitosterol as the dominant plant sterol and palmitic, linoleic, and linolenic acids and esters. The 3 plants differed significantly in the observed terpene and terpenoid composition. Germacrene D-4-ol, known to have antifungal activity, was the major terpenoid identified in P pumila (7.42%-7.76%), phytol (4.13%), α-cadinene (3.96%), and cadina-1,4-diene (5.53%) were observed in L canadensis treatments, and squalene (2.20%-7.04%), phytol (4.17%), and cadina-1,4-diene (6.68%) were observed in B cylindrica treatments . Possible rationales for Native American medicinal uses were evaluated.

Combination Therapy as a Strategy to Control Infections Caused by Multi-resistant Bacteria: Current Review

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Antimicrobial Resistance (AMR) is one of the main challenges of today's medicine because it has become a global problem that affects the treatment of multiple infections and impacts public health. This resistance is caused as the bacteria generate selective pressure-promoting mechanisms to evade the action of conventional drugs, which are also associated with adverse effects. Infections caused by these multi-resistant bacteria potentially reduce the possibility of effective therapy; this situation increases morbidity and mortality and treatment costs. Therefore, to establish combined therapy as a strategy for the control of infections caused by multi-resistant bacteria, a bibliographic search was carried out between 2015 and 2020 in databases such as PubMed, Scopus and Science Direct. The exhaustive review of the articles allowed a critical analysis of the information. Mechanisms were identified for obtaining drugs with antimicrobial potential, their biological activity and the possible effect of their combination against multidrug-resistant bacteria as an alternative for infectious disease control and as a response to reduce the use of antibiotics. Combined therapy is presented as an innovative therapeutic alternative, which uses non-antibiotic substances that can be obtained by three routes: the repositioning of drugs, synthetic substances and natural products. In this way, important elements are provided to guide researches that seek to reduce antimicrobial resistance.

Antibacterial plant compounds, extracts and essential oils: An updated review on their effects and putative mechanisms of action

BACKGROUND

Antibiotic-resistant bacteria pose a global health threat. Traditional antibiotics can lose their effectiveness, and the development of novel effective antimicrobials has become a priority in recent years. In this area, plants represent an invaluable source of antimicrobial compounds with vast therapeutic potential.

PURPOSE

To review the full possible spectrum of plant antimicrobial agents (plant compounds, extracts and essential oils) discovered from 2016 to 2021 and their potential to decrease bacterial resistance. Their activities against bacteria, with special emphasis on multidrug resistant bacteria, mechanisms of action, possible combinations with traditional antibiotics, roles in current medicine and future perspectives are discussed.

METHODS

Studies focusing on the antimicrobial activity of compounds of plant origin and their mechanism of action against bacteria were identified and summarized, including contributions from January 2016 until January 2021. Articles were extracted from the Medline database using PubMed search engine with relevant keywords and operators.

RESULTS

The search yielded 11,689 articles from 149 countries, of which 101 articles were included in this review. Reports from 41 phytochemicals belonging to 20 families were included. Reports from plant extracts and essential oils from 39 plant species belonging to 17 families were also included. Polyphenols and terpenes were the most active phytochemicals studied, either alone or as a part of plant extracts or essential oils. Plasma membrane disruption was the most common mechanism of antimicrobial action. Number and position of phenolic hydroxyl groups, double bonds, delocalized electrons and conjugation with sugars in the case of flavonoids seemed to be crucial for antimicrobial capacity. Combinations of phytochemicals with beta-lactam antibiotics were the most studied, and the inhibition of efflux pumps was the most common synergistic mechanism.

CONCLUSION

In recent years, terpenes, flavones, flavonols and some alkaloids and phenylpropanoids, either isolated or as a part of extracts, have shown promising antimicrobial activity, being membrane disruption their most common mechanism. However, their utilization as appropriate antimicrobials need to be boosted by means of new omics technologies and network pharmacology to find the most effective combinations among them or in combination with antibiotics.

Antibacterial and Antifungal Activities of Ethiopian Medicinal Plants: A Systematic Review

Background: Podoconiosis and lymphatic filariasis are the most common causes of lower limb lymphoedema in the tropics. Many sufferers experience frequent painful episodes of acute bacterial infection. Plant based traditional medicines are used to treat infections in many countries and are culturally established in Ethiopia. Ethiopian medicinal plants found to have antibacterial and antifungal activities were reviewed with the aim of increasing information about the treatment of wound infections in patients with lymphoedema. Methods: This study collates data from published articles on medicinal plants with antibacterial and antifungal activities in Ethiopia. A systematic search of Scopus, EMBASE, PUBMED/MEDLINE and Google Scholar was undertaken. The Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) guidelines were followed. The protocol was registered on PROSPERO with registration number CRD42019127471. All controlled studies of in vitro antibacterial and antifungal activities were considered. All articles containing the descriptors published until June 28, 2019 were included. The outcome was measured as percent inhibition of microbial growth. For quality assessment of individual in vitro studies, OECD guidelines and the WHO-Good Laboratory Practice (GLP) handbook were used. Results: Seventy-nine studies met the inclusion criteria. A total of 150 plant species and three compounds had been tested against 42 species of bacteria, while 43 plant species had been tested against 22 species of fungus. Conclusion: Materials derived from several Ethiopian medicinal plants have been shown to have promising activity against a variety of bacteria and fungi. Those derived from Azadiractha indica A. Juss. and Lawsonia inerms L. are the most extensively studied against a wide range of gram-negative and positive bacteria, and fungal species.

Defying Multidrug Resistance! Modulation of Related Transporters by Flavonoids and Flavonolignans

Multidrug resistance (MDR) is a major challenge for the 21th century in both cancer chemotherapy and antibiotic treatment of bacterial infections. Efflux pumps and transport proteins play an important role in MDR. Compounds displaying inhibitory activity toward these proteins are prospective for adjuvant treatment of such conditions. Natural low-cost and nontoxic flavonoids, thanks to their vast structural diversity, offer a great pool of lead structures with broad possibility of chemical derivatizations. Various flavonoids were found to reverse both antineoplastic and bacterial multidrug resistance by inhibiting Adenosine triphosphate Binding Cassette (ABC)-transporters (human P-glycoprotein, multidrug resistance-associated protein MRP-1, breast cancer resistance protein, and bacterial ABC transporters), as well as other bacterial drug efflux pumps: major facilitator superfamily (MFS), multidrug and toxic compound extrusion (MATE), small multidrug resistance (SMR) and resistance-nodulation-cell-division (RND) transporters, and glucose transporters. Flavonoids and particularly flavonolignans are therefore highly prospective compounds for defying multidrug resistance.

Antibiotic resistance genes are abundant and diverse in raw sewage used for urban agriculture in Africa and associated with urban population density

A comparative study was conducted to (1) assess the potential of raw sewage used for urban agriculture to disseminate bacterial resistance in two cities of different size in Cameroon (Central Africa) and (2) compare the outcome with data obtained in Burkina Faso (West Africa). In each city, raw sewage samples were sampled from open-air canals in three neighbourhoods. After DNA extraction, the microbial population structure and function, presence of pathogens, antibiotic resistance genes and Enterobacteriaceae plasmids replicons were analysed using whole genome shotgun sequencing and bioinformatics. Forty-three pathogen-specific virulenc e factor genes were detected in the sewage. Eighteen different incompatibility groups of Enterobacteriaceae plasmid replicon types (ColE, A/C, B/O/K/Z, FIA, FIB, FIC, FII, H, I, N, P, Q, R, T, U, W, X, and Y) implicated in the spread of drug-resistance genes were present in the sewage samples. One hundred thirty-six antibiotic resistance genes commonly associated with MDR plasmid carriage were identified in both cities. Enterobacteriaceae plasmid replicons and ARGs found in Burkina Faso wastewaters were also present in Cameroon waters. The abundance of Enterobacteriaceae, plasmid replicons and antibiotic resistance genes was greater in Yaounde, the city with the greater population. In conclusion, the clinically relevant environmental resistome found in raw sewage used for urban agriculture is common in West and Central Africa. The size of the city impacts on the abundance of drug-resistant genes in the raw sewage while ESBL gene abundance is related to the prevalence of Enterobacteriaceae along with plasmid Enterobacteriaceae abundance associated to faecal pollution.

Syzygium jambos Displayed Antibacterial and Antibiotic-Modulating Activities against Resistant Phenotypes

The present study was designed to evaluate the antibacterial activities of methanol extracts of bark and leaves of Syzygium jambos, as well as their synergistic effects with selected antibiotics against drug-resistant Gram-positive and Gram-negative bacteria. The crude extracts were subjected to qualitative phytochemical screening; broth microdilution method was used for antibacterial assays. Phytochemical studies indicate that leaves and bark extracts contained polyphenols, anthraquinones, tannins, and steroids. Extract of the leaves was active against all the 26 strains of Staphylococcus aureus and all the 21 strains of Gram-negative bacteria tested, within the minimum inhibitory concentration (MIC) range of 32–512 μg/mL. The lowest MIC value of 32 μg/mL was obtained with extract of the leaves against Staphylococcus aureus MRSA9 strain. In Gram-negative bacteria, the lowest MIC value of 64 μg/mL was also obtained against Enterobacter aerogenes EA294 and Klebsiella pneumoniae K24 strains. Against S. aureus strains, antibiotic-modulating activity of extracts at MIC/2 towards more than 70% of the tested strains was obtained when leaves and bark extracts were tested in association with chloramphenicol (CHL). This was also the case when leaves extract was combined with CHL, kanamycin (KAN), tetracycline (TET), and erythromycin (ERY) and when bark extract was combined with ciprofloxacin (CIP), TET, and ERY against Gram-negative bacteria. In conclusion, this study demonstrated that Syzygium jambos has antibacterial and antibiotic-modulating activities.

The anti-Staphylococcus aureus activity of the phenanthrene fraction from fibrous roots of Bletilla striata

Background

Bletillae Rhizoma, the tuber of Bletilla striata, has been used in Chinese traditional medicine to treat infectious diseases. Chemical studies indicated that phenanthrene was one of the most important components of the herb, with a broad spectrum of antibiotic activity against Gram-positive bacteria. The objective of this study was to further characterize the antibacterial activity of the phenanthrene fraction from the fibrous root of the pseudobulb of B. striata.

Methods

The phenanthrene fraction (EF60) from the ethanol extract of fibrous roots of Bletilla striata pseudobulbs was isolated using polyamide column chromatography. The antibacterial activity of the fraction was evaluated in vitro using a 96-well microtiter plate and microbroth dilution method. The cytotoxicity of EF60 against mammalian cells was tested by hemolysis and MTT assays.

Results

EF60 was obtained using alcohol extraction and polyamide column chromatography, with a yield of 14.9 g per 1 kg of the fibrous roots of B. striata. In vitro tests indicated that EF60 was active against all tested strains of Staphylococcus aureus, including clinical isolates and methicillin-resistant S. aureus (MRSA). The minimum inhibitory concentration (MIC) values of EF60 against these pathogens ranged from 8 to 64 μg/mL. Minimum bactericidal concentration tests demonstrated that EF60 was bactericidal against S. aureus 3304 and ATCC 29213 and was bacteriostatic against S. aureus 3211, ATCC 25923, and ATCC 43300. Consistently, the time-kill assay indicated that EF60 could completely kill S. aureus ATCC 29213 at 2× the MIC within 3 h but could kill less than two logarithmic units of ATCC 43300, even at 4× the MIC within 24 h. The postantibiotic effects (PAE) of EF60 (4× MIC) against strains 29213 and 43300 were 2.0 and 0.38 h, respectively. Further studies indicated that EF60 (160 μg/mL) showed no cytotoxicity against human erythrocytes, and was minimally toxic to Human Umbilical Vein Endothelial Cells with an IC₅₀ of 75 μg/mL.

Conclusions

Our studies indicated that EF60 is worthy of further investigation as a potential phytotherapeutic agent for treating infections caused by S. aureus and MRSA.

Electronic supplementary material

The online version of this article (doi:10.1186/s12906-016-1488-z) contains supplementary material, which is available to authorized users.