Antibacterial and antibiotic resistance modulatory activities of leaves and bark extracts of Recinodindron heudelotii (Euphorbiaceae) against multidrug-resistant Gram-negative bacteria

Phytochemical Composition, Antibacterial, and Antibiotic-Resistance Modulatory Activity of Extracts of Lippia multiflora Moldenke, Terminalia mollis M. A. Lawson, and Cinchona officinalis L. Against Multidrug-Resistant Pseudomonas aeruginosa

Pseudomonas aeruginosa is a critical-class pathogen that shows great resistance to most conventional antibiotics. Hence, it is of utmost importance to search for novel drugs to fight infections caused by this bacterium. This study aimed to evaluate the antibacterial activity of Lippia multiflora, Terminalia mollis, and Cinchona officinalis extracts alone and in combination with antibiotics against multidrug-resistant (MDR) P. aeruginosa. Phytochemical analysis was performed using standard qualitative and quantitative assays. The microdilution method was used to assess the antibacterial and antibiotic-resistance modulatory activity of the extracts. The interaction between antibiotics and Cinchona officinalis leaf extract was carried out using the checkerboard broth microdilution method. Phenols and flavonoids were detected in all extracts, whereas other phytochemical classes were selectively distributed. T. mollis leaf extract demonstrated the highest phenolic content (151.59 mg GAE/g), while L. multiflora leaf (LML) extract showed the highest flavonoid content (24.51 mg QE/g). These extracts exhibited antibacterial activity, with minimum inhibitory concentrations (MICs) ranging from 128 to 2048 μg/mL. LML extract displayed the best antipseudomonal activity, with MIC of 128 μg/mL against ATCC 27853 and 256 μg/mL against some MDR isolates (PA1, PA2, and PA7). Moreover, C. officinalis leaf extract (MIC/8), although weakly active, had improved by 2 to 64-fold the activity of imipenem, streptomycin, kanamycin, and ceftriaxone against MDR P. aeruginosa. It also showed synergy (ΣFIC ≤ 0.5) with streptomycin, ampicillin, tetracycline, and vancomycin against P. aeruginosa PA3. The overall results indicate that the tested extracts, especially those from L. multiflora and C. officinalis leaves, necessitate further exploration for the development of natural drugs to treat infections caused by MDR P. aeruginosa.

The role of hydroponic solution of Ulva fasciata in modulating the antibiotic resistance of Vibrio alginolyticus

AIMS

This study aimed to ascertain the active substances in the hydroponic solution of Ulva (U.) fasciata (HSUF) and their effects on antibiotics resistance of pathogenic bacteria Vibrio alginolyticus (Va.) at environmental levels.

METHODS AND RESULTS

Analytical results of HSUF by solid-phase extraction and gas chromatography-mass spectrometry showed that HSUF contained rich active substances and dominated by 2,4,6-tribromophenol, acetal, mono (2-ethylhexyl) phthalate, and 2-(4-hydroxybenzene) ethanol, etc. Thereinto, 2,4,6-tribromophenol had the lowest minimal inhibitory concentrations of 64-128 μg ml-1 for Va. strains. The rich antibacterial substances of HSUF inhibited 47%-63% of isolated Va. strains. After 20 generations of subculture for Va. strains in three dilutes [1/2 (HT), 1/20 (MT), and 1/50 (LT)] of HSUF (20 g l-1), the resistance to streptomycin of Va. S1 and Va. M3 changed from intermediate resistance ability to susceptible level. The large promotion of reactive oxygen species was observed in different HSUF levels, but the biofilm formation of Va. S1 did not change significantly. Transcriptome sequencing of Va. S1 demonstrated that antibiotic resistance gene lpxA was downregulated at different HSUF levels.

CONCLUSIONS

Live U. fasciata excreted a variety of active secondary metabolites in HSUF, which exhibited strong inhibitory effects on three isolated Va. strains. HSUF changed the antibiotic resistance of Va. Strain, especially at higher HSUF concentrations.

Potential role of Manilkara Zapota L in treating bacterial infection

The increasing problem of antibiotic resistance in bacteria leads to an urgent need for new antimicrobial agents. Alternative treatments for bacterial infections need to be explored to tackle this issue. Plant-based substances are emerging as promising options. Manilkara zapota L. contains compounds with antibiotic activities, and anti-inflammatory, antitumor, antipyretic, and antioxidant properties. It has medicinal properties and contains bioactive compounds, like tannins, flavonoids, and triterpenoids. This review aimed to comprehensively evaluate the existing literature on the potential medicinal and therapeutic benefits of M. zapota in bacterial infections by utilizing data from in vivo and in vitro studies. M. zapota has the potential to be a nutritional source of antimicrobial food. Numerous preclinical studies have demonstrated the antibacterial activities of M. zapota and its components. The antibacterial mechanisms of this fruit could interact with bacterial cell structures such as cell walls or membranes.

Antibiotics resistance evolution of isolated Vibrio parahaemolyticus from mariculture under the continuous culture of sub-inhibitory concentrations of Ulva fasciata hydroponic solution

The outbreak of vibriosis from Vibrio (V.) parahaemolyticus is widespread in the mariculture, and live macroalgae has been considered to be effective and eco-friendly approach for the control of vibriosis. Three V. parahaemolyticus strains with β-lactam antibiotics resistance (resistant to ampicillin (AM), amoxicillin (AMX)) were isolated from mariculture in study, and the antibiotics resistance evolution mechanism was examined at the sub-inhibitory concentration (SIC) of hydroponic solution of Ulva (U.) fasciata (HSUF). The HSUF with the highest density (20 g fresh weight U. fasciata L^-1) demonstrated the strongest inhibitory rates (47.0 %-65.8 %) on the three strains during the stable phase (8-24 h) of growth curve, which indicated that the HSUF (≤20 g L^-1) could be considered to be at SIC for V. parahaemolyticus strains. After continuous subculture of V. parahaemolyticus with three dilutes (1/2 (HT), 1/20 (MT) and 1/50 (LT)) of HSUF (20 g L^-1), all the strains of 20th generation were still resistant to AM and AMX. However, the LT condition reduced MIC of AM (2-16 times) and AMX (0-2 times) to strains, while MT and HT showed significantly various effect of β-lactam antibiotics resistance on different strains. The biofilm formation and ROS content of V. parahaemolyticus were almost positively correlated to the concentrations of HSUF. Transcriptome sequencing analysis of a representative strain showed that the lower concentrations of HSUF caused more down-regulated DEGs of the strains, and more down-regulated (vmeA, vmeB, sapA, mrdA) DEGs of strains were related to the pathway of β-lactam antibiotics resistance at LT condition. Thus, low concentration of HSUF was seemed to have better improvement for V. parahaemolyticus strains resistant to β-lactam antibiotics, which were mainly related to the impairment of biofilm formation, ROS and efflux pump.

In Silico Docking, Resistance Modulation and Biofilm Gene Expression in Multidrug-Resistant Acinetobacter baumannii via Cinnamic and Gallic Acids

Despite the mounting global burden of antimicrobial resistance (AMR), the generation of new classes of effective antimicrobials still lags far behind. The interplay between multidrug resistance and biofilm formation in Acinetobacter baumannii has drastically narrowed the available therapeutic choices. The use of natural compounds holds promise as an alternate option for restoring the activity of existing antibiotics and attenuating virulence traits through reduced biofilm formation. This study aimed to evaluate the modulatory effect of combining cinnamic and gallic acids at ½MIC with various antibiotics against multidrug-resistant (MDR) A. baumannii clinical isolates as well as study the effect on the expression of the biofilm-associated genes (bap, csuE, ompA) via quantitative, real-time PCR. Combining cinnamic or gallic acid with imipenem, amikacin or doxycycline resulted in significant reduction of resistance (p < 0.05). On the contrary, no effect was recorded when both acids were combined with levofloxacin, and only cinnamic acid had a synergistic effect with colistin. The transcriptomic changes of biofilm-related genes in the presence of gallic acid at ½MIC were compared with untreated control samples. The fold expression values proved that gallic acid substantially down-regulated the respective genes in all five strong biofilm formers. Molecular docking studies of gallic and cinnamic acids on target genes revealed good binding affinities and verified the proposed mechanism of action. To the best of our knowledge, this is the first report on the effect of gallic acid on the expression of bap, csuE and ompA genes in A. baumannii, which may permit its use as an adjunct anti-virulence therapeutic strategy.

Exploring New Sources of Bioactive Phenolic Compounds from Western Balkan Mountains

This study presents the first report on phenolic composition and bioactivity of ethanolic extracts of three plant species that grow in the western Balkan mountains and are used in traditional folk medicine: Valeriana montana, Salix retusa, and Campanula hercegovina. Phenolics were extracted from different aerial plant parts using 80% ethanol to assess the possibility of sustainable use of these plants as a source of bioactive compounds without disruption to the roots (for V. montana) or destruction of whole habitats (for S. retusa and C. hercegovina). The ethanolic extract of V. montana flower contained noticeable levels of apigenin and quercetin. The branches and bark of S. retusa were significantly rich in catechin, while rutin was the major phenolic found in the leaf extract of C. hercegovina. Furthermore, the flower extract of V. montana revealed the best antioxidant activity, which was comparable to 4-hydroxybenzoic acid and quercetin. Considering antimicrobial activity, the leaf extracts of V. montana and C. hercegovina demonstrated potent activity against all microbes tested, while the extracts of S. retusa were moderately effective. The presented results emphasize the potential of these plants as novel sources of bioactive compounds.

Botanicals and phytochemicals from the bark of Hypericum roeperianum (Hypericaceae) had strong antibacterial activity and showed synergistic effects with antibiotics against multidrug-resistant bacteria expressing active efflux pumps

ETHNOPHARMACOLOGICAL RELEVANCE

Infections due to multidrug-resistant (MDR) bacteria constitute a real problem in the public health worldwide. Hypericum roeperianum Schimp. ex A. Rich (Hypericaceae) is used traditionally for treatment of various ailments such as abdominal pains, constipation, diarrhea, indigestion, nausea, and bacterial diseases.

AIM OF THE STUDY

This study was aimed at investigating the antibacterial and antibiotic-modifying activity of the crude methanol extracts (HRB), ethyl-acetate soluble fraction (HRBa), residual material (HRBb), and 11 compounds from the bark of Hypericum roeperianum against multi-drug resistant (MDR) bacteria expressing active efflux pumps.

MATERIALS AND METHODS

The antibacterial activity, the efflux pump effect using the efflux pump inhibitor (EPI), phenylalanine-arginine-ß-naphthylamide (PAβN), as well as the antibiotic-modifying activity of samples were determined using the broth micro-dilution method. Spectrophotometric methods were used to evaluate the effects of HRB and 8,8-bis(dihydroconiferyl) diferulate (11) on bacterial growth, and bacterial membrane damage, whereas follow-up of the acidification of the bacterial culture was used to study their effects on bacteria proton-ATPase pumps.

RESULTS

The crude extract (HRB), HRBa, and HRBb had selective antibacterial activity with MICs ranging from 16 to 512 μg/mL. Phytochemical 11 displayed the best antibacterial activity (0.5 ≤ MIC ≤ 2 μg/mL). The activity of HRB and 11 in the presence of EPI significantly increased on the tested bacteria strains (up to 32-fold). The activity of cloxacillin (CLO), doxycycline (DOX), and tetracycline (TET), was considerably improved (up to 64-fold) towards the multidrug-resistant Enterobacter aerogenes EA-CM64 strain. The crude extract (HRB) and 11 induced the leakage of bacterial intracellular components and inhibited the proton-ATPase pumps.

CONCLUSIONS

The crude extract (HRB) and 8,8-bis(dihydroconiferyl)diferulate from the bark of Hypericum roeperianum are good antibacterial candidates that deserve further investigations to achieve antibacterial drugs to fight infections involving MDR bacteria.

Phytochemical Analysis and Investigation of the Antimicrobial and Cytotoxic Activities of Croton dichogamus Pax Crude Root Extracts

Background

Increasing antimicrobial resistance has led to an arduous search for new potent drugs from nature. In this search, plants have proved to be rich reservoirs of efficacious medicinal components that manage ailments. The current study is designed to investigate the phytochemical composition, antimicrobial activity, and the cytotoxicity of the crude root extracts of Croton dichogamus, a shrub that is commonly used in the eastern Africa for the management of infectious diseases.

Methods

The roots of Croton dichogamus were obtained, dried, ground, and extracted using three solvents (acetone, distilled water, and 50% ethanol). The antimicrobial activity was tested using agar well diffusion and microbroth dilution techniques against five human pathogens. The brine shrimp lethality assay was used to assess the toxic effect.

Results

The phytochemical screening indicated the presence of terpenoids, flavonoids, tannins, phenols, polyuronides, saponins, and anthracenes. The brine shrimp lethality assay indicated that all the extracts were highly cytotoxic with LC₅₀ values below 100 μg/ml. Acetonic extract had an LC₅₀ value of 4.148 μg/ml, hydroethanolic extract had 76.09 μg/ml, and aqueous extract had 42.61 μg/ml. All extracts showed the antibacterial activity against Gram-positive bacteria (B. cereus and S. aureus) and a fungal organism, C. albicans. The extracts showed no antibacterial effect on the Gram-negative bacterial strains (P. aeruginosa and E. coli) at a concentration of 250 mg/ml. The highest antimicrobial activity was demonstrated by the acetonic extract on B. cereus which had an MIC of 10.42 mg/ml and a zone of inhibition of 17.33 ± 0.58 at a concentration of 250 mg/ml.

Conclusion

In this research work, we report that C. dichogamus had the antimicrobial activity confirming the folklore claim. The results made a strong case for isolation of novel anticancer lead compounds.

Development and Evaluation of Antimicrobial and Modulatory Activity of Inclusion Complex of Euterpe oleracea Mart Oil and β-Cyclodextrin or HP-β-Cyclodextrin

The development of inclusion complexes is used to encapsulate nonpolar compounds and improve their physicochemical characteristics. This study aims to develop complexes made up of Euterpe oleracea Mart oil (EOO) and β-cyclodextrin (β-CD) or hydroxypropyl-β-cyclodextrin (HP-β-CD) by either kneading (KND) or slurry (SL). Complexes were analyzed by molecular modeling, Fourier-transform infrared spectroscopy, scanning electron microscopy, powder X-ray diffraction, thermogravimetry analysis and differential scanning calorimetry. The antibacterial activity was expressed as Minimum Inhibitory Concentration (MIC), and the antibiotic resistance modulatory activity as subinhibitory concentration (MIC/8) against Escherichia coli, Streptomyces aureus, Pseudomonas aeruginosa and Enterococcus faecalis. Inclusion complexes with β-CD and HP-β-CD were confirmed, and efficiency was proven by an interaction energy between oleic acid and β-CD of -41.28 ± 0.57 kJ/mol. MIC values revealed higher antibacterial activity of complexes compared to the isolated oil. The modulatory response of EOO and EOO-β-CD prepared by KND as well as of EOO-β-CD and EOO-HP-β-CD prepared by SL showed a synergistic effect with ampicillin against E. coli, whereas it was not significant with the other drugs tested, maintaining the biological response of antibiotics. The antimicrobial response exhibited by the complexes is of great significance because it subsidizes studies for the development of new pharmaceutical forms.

Novel approach to combat antibiotic resistance: evaluation of some Armenian herb crude extracts for their antibiotic modulatory and antiviral properties

AIMS

One of the strategies to combat antibiotic resistance can be the use of plant materials in combination with antibiotics, taking into account that phytochemicals can act as antibiotic resistance-modifying agents. This can give a second life to the traditional antibiotics. The aim was to evaluate antibiotic modulatory effect of crude extracts from Agrimonia eupatoria, Hypericum alpestre, Rumex obtusifolius and Sanguisorba officinalis herbs towards several commercial antibiotics using some Gram-positive and Gram-negative bacteria.

METHODS

The antibiotic modulatory activity was tested by determining MICs of antibiotics in the absence and presence of plant crude extracts at subinhibitory concentrations. Antiviral potential of different extracts of tested plant materials was also explored by double overlay plaque assay.

RESULTS

The tested plant crude extracts exhibited high modulatory activity towards used antibiotics. Particularly, high modulatory activity was observed with extracts of H. alpestre and R. obtusifolius. Many plant-antibiotic combinations induced the decrease in MICs of antibiotics up to ~fourfold indicating synergy. Moreover, the similar change was observed at both subinhibitory concentrations (MIC/2 and MIC/4) of the same plant crude extract. High anti-phage activity of plants with the exception of Lilium armenum against T4 phage of Escherichia coli C-T4 was also shown.

CONCLUSIONS

Plant crude extract or commercial antibiotic combinations significantly increased the efficiency of antibiotics. Tested plant materials with exception of L. armenum have antiviral property.

SIGNIFICANCE AND IMPACT OF THE STUDY

For the first time, antibiotic modulatory activity of tested herb extracts was shown, which could have potential in practical applications. Tested plant materials with exception of L. armenum could have prospective, as a source of new antiviral compounds.

Antibacterial and Antibiotic Modifying Potential of Crude Extracts, Fractions, and Compounds from Acacia polyacantha Willd. against MDR Gram-Negative Bacteria

The present study aimed to assess the in vitro antibacterial and antibiotic modifying activities of methanol extracts prepared from the leaf (APL) and bark (APB) of Acacia polyacantha, fractions (APLa-d) and compounds isolated from APL against a panel of multidrug resistant (MDR) Gram-negative bacteria. Leaf extract was subjected to column chromatography for compounds isolation; antibacterial assays were performed on samples alone and with an efflux pump inhibitor (EPI), respectively, and several antibiotics on the tested bacteria. The phytochemical investigation of APL led to the isolation of stigmasterol (1), β-amyrin (2), 3-O-β-_D-glucopyranosylstigmasterol (3), 3-O-methyl-D-chiro-inositol (4), epicatechin (5), quercetin-3-O-glucoside (6), 3-O-[β-_D-xylopyranosyl-(1→4)-β-_D-galactopyranosyl]-oleanolic acid (7), and 3-O-[β-galactopyranosyl-(1→4)-β-_D-galactopyranosyl]-oleanolic acid (8). APL and APB had minimal inhibitory concentration (MIC) values ≤ 1024 μg/mL on 73.3% and 46.7% of the tested bacteria, respectively. APLb and APLd were effective against 88.9% of tested bacterial species with compound 8 showing the highest activity inhibiting 88.9% of tested bacteria. The EPI, phenylalanine-arginine-β-naphthylamide (PAßN), strongly improved the activity of APL, APLb, APLd, and compound 8 on all tested bacteria. Synergistic effects were obtained when APL and compounds 7 and 8 were combined with erythromycin (ERY), gentamycin (GEN), ciprofloxacin (CIP), and norfloxacin (NOR). The present study demonstrates the antibacterial potential of Acacia polyacantha and its constituents to combat bacterial infections alone or in combination with EPI.

Antibacterial and Antibiotic-Potentiating Activities of Thirteen Cameroonian Edible Plants against Gram-Negative Resistant Phenotypes

This work was designed to investigate the antibacterial activities of methanol extracts from thirteen Cameroonian edible plants and their antibiotic-potentiating effects against Gram-negative multidrug-resistant (MDR) phenotypes. The broth microdilution method was used to evaluate the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of the extracts, as well as their antibiotic-potentiating activities. The phytochemical screening of the extracts was carried out according to the standard methods. The results of phytochemical tests revealed the presence of sterols, polyphenols, and tannins in most of the tested extracts, with the other classes of secondary metabolites being selectively distributed. Tested extracts showed variable antibacterial activities with MIC values ranging from 64 to 1024 μg/mL. However, some extracts were significantly active against certain bacterial strains: seeds extract of Theobroma cacao (64 μg/mL) against Escherichia coli AG100Atet and Klebsiella pneumoniae K24, and the bark extract of Uapaca guineensis against E. coli ATCC 8739. The leaves extract of T. cacao displayed the best MBC values (256 μg/mL) against E. aerogenes EA27. Some tested extracts included extracts from the leaves of T. cacao and P. vulgaris, and the seeds of D. edulis and barks A. indica has selectively improved (2- to 64-fold) the antibacterial activities of some of the tested antibiotics, chloramphenicol (CHL), tetracycline (TET), kanamycin (KAN), streptomycin (STR), and erythromycin (ERY), against more than 70% of tested MDR bacteria. The findings of this work showed that tested plant extracts and particularly those from T. cacao and Phaseolus vulgaris can be used alone or in combination with conventional antibiotics in the treatment of infections involving multiresistant bacteria.

Antistaphylococcal and Antibiotic Resistance Modulatory Activities of Thirteen Cameroonian Edible Plants against Resistant Phenotypes

Background

In this study, 18 methanol extracts from Cameroonian edible plants were tested for their antibacterial activities against 26 strains of S. aureus; the role of efflux pumps in the resistance of tested bacteria and the antibiotic resistance-modulating activities against selected multidrug-resistant (MDR) phenotypes were also investigated.

Methods

Broth microdilution assay was used to evaluate the antibacterial activity, the role of efflux pumps, and the antibiotic resistance-modulating effects of plant extracts.

Results

Extracts from Dacryodes edulis seeds (DES) and Dacryodes edulis bark (DEB) were active against all 26 tested bacterial strains, within the minimal inhibitory concentration (MIC) range of 256–1024 µg/mL. MIC values varied from 64 to 1024 µg/mL against 96.2% of the 26 tested bacteria for Phaseolus vulgaris leaves (PVL), 92.3% for Azadirachta indica bark (AIB), Dacryodes edulis leaves (DEL), and Ricinodendron heudelotii leaves (RHL). The lowest MIC value of 64 µg/mL was obtained with the extract from Cucurbita maxima beans (CMB) against MRSA4 strain and from Uapaca guineensis bark (UGB) against MRSA9 strain. Bacterial efflux pump inhibitor (EPI), carbonyl cyanide m-chlorophenyl hydrazone (CCCP), improved the activity of DES and UGB as well as that of extracts from Hibiscus esculentus leaves (HEL) and Uapaca guineensis leaves (UGL) against resistant S. aureus strains. Antibiotic-modulating effects against more than 70% of the S. aureus strains tested were obtained when RHL (at MIC/2) was combined with CIP, ERY, and KAN (88.89%), CHL (88.89%), TET (77.78%), and STR (88.89%).

Conclusion

The present study demonstrated that the 13 tested plants had antistaphylococcal effects and that DES, HEL, UGL, and UGB could be used in combination with EPI to combat resistance to Staphylococcus aureus. Also, it demonstrated that some studied extracts and mostly RHL could be used as antibiotic resistance modulators to fight against resistant strains of S. aureus.

Effect of Fractioning on Antibacterial Activity of Enantia chlorantha Oliver (Annonaceae) Methanol Extract and Mode of Action

Infectious diseases caused by bacteria constitute the main cause of morbidity and mortality throughout the world and mainly in developing countries. In this work, the influence of fractioning and the mode of action of stem barks methanol extract of Enantia chlorantha were investigated. The aim was to optimize the antibacterial activity of the methanol extract. The extract was prepared by maceration of barks powder in methanol. Fractioning was done using increasing solvents polarity. Standard phytochemical methods were used for phytochemical screening. Minimum Inhibitory Concentrations (MIC) and Minimum Bactericidal Concentration (MBC) of the methanol extract and fractions were determined using broth microdilution method. The studied mode of action of both methanol extract and n-butanol fraction included antibiofilm activity, H+-ATPase-mediated proton pumping assay, salt tolerance, and cells cycle. The methanol extract of E. chlorantha stem barks was found to be active on all the bacteria tested (32 ≤ MIC ≤ 512 μg/mL), its activity being significant (MIC < 100 μg/ml) out of 5 of the 28 clinical isolates used. Salmonella enterica serovar paratyphi A was the most sensitive (32 μg/mL). Compared to the extract and other fractions, the n-butanol fraction was found to be more active (32 ≤ MIC ≤ 256). Significant antibacterial activity of this fraction was observed out of 10 of the 28 bacterial isolates and 3 out of 7 bacterial strains. Lowest MIC values (32 μg/ml) of this fraction were obtained with Escherichia coli (136), Pseudomonas aeruginosa (CIP 76110), and Salmonella enterica serovar typhi 9. The methanol extract of E. chlorantha and its n-butanol fraction revealed several modes of action including the prolongation of the latency phase of the bacterial growth, the inhibition of the pump with protons H⁺ - ATPases bacterial, the loss of the salt tolerance of the Staphylococcus aureus, and inhibition of the formation of the bacterial biofilm. The present results showed that the n-butanol fraction of the methanol stem barks extract of E. chlorantha possess the essential antibacterial components and could best be used to fight against bacterial infections as compared to methanol extract.

Tristemma hirtum and Five Other Cameroonian Edible Plants with Weak or No Antibacterial Effects Modulate the Activities of Antibiotics against Gram-Negative Multidrug-Resistant Phenotypes

In order to contribute to the fight against infectious diseases, the in vitro antibacterial activity and the antibiotic-potentiating effects of Tristemma hirtum and five other Cameroonian edible plants have been evaluated against Gram-negative multidrug-resistant (MDR) phenotypes. The microdilution method was used to evaluate the bacterial susceptibility of the extracts and their combination to common antibiotics. The phytochemical screening of the extracts was carried out according to standard methods. Phytochemical analysis of the extracts revealed the presence of alkaloids, triterpenes, steroids, and polyphenols, including flavonoids in most of the tested extracts. The entire tested extracts showed moderate (512 μg/mL ≤ MIC ≤ 2048 μg/mL) to weak (MIC > 2048 μg/mL) antibacterial activities against the tested bacteria. Furthermore, extracts of leaf of Tristemma hirtum and pericarps of Raphia hookeri (at their MIC/2 and MIC/4) strongly potentiated the activities of all antibiotics used in the study, especially those of chloramphenicol (CHL), ciprofloxacin (CIP), kanamycin (KAN), and tetracycline (TET) against 70% (7/10) to 100% (10/10) of the tested MDR bacteria, with the modulating factors ranging from 2 to 128. The results of this study suggest that extracts from leaves of Tristemma hirtum and pericarps of Raphia hookeri can be sources of plant-derived products with antibiotic modifying activity.

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.