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. 2016 Oct 10;16:388. doi: 10.1186/s12906-016-1371-y

Antibacterial activity of six medicinal Cameroonian plants against Gram-positive and Gram-negative multidrug resistant phenotypes

Igor K Voukeng 1, Veronique P Beng 2, Victor Kuete 1,✉
PMCID: PMC5057269  PMID: 27724917

Abstract

Background

Infectious diseases due to multidrug-resistant bacteria are one of the causes of treatment failures contributing to an increase in mortality and/or morbidity. In this study, we evaluated the antibacterial potential of different parts of six medicinal plants namely Alstonia boonei, Ageratum conyzoides, Croton macrostachys, Cassia obtusifolia, Catharanthus roseus and Paullinia pinnata against a panel of 36 multi-drug resistant (MDR) Gram-negative and Gram-positive bacteria.

Methods

Minimum Inhibitory Concentration (MIC) and Minimal Bactericidal Concentration (MBC) of the methanol extracts from different parts of the plants were determined using broth microdilution method; standard phytochemical methods were used for phytochemical screening.

Results

Several phytochemical classes such as polyphenols, sterols, triterpenes, alkaloids, flavonoids and saponins were identified in the plant extracts. MIC values obtained ranged from 64 to 1024 μg/mL. Leaves extract of Catharanthus roseus (86.11 %), Croton macrostachys (83.33 %) and Paullinia pinnata (80.55 %) displayed the best antibacterial spectra. The lowest MIC value of 64 μg/mL was obtained with the Paullinia pinnata stems extract and Cassia obtusifolia extract against the strain of Staphylococcus aureus MRSA8. Results also showed that the tested samples generally displayed bacteriostatic effects with MBC values obtained in only 3.35 % of the cases where plant extracts were active.

Conclusion

The results obtained at the end of this study demonstrate for the first time the antibacterial activity of the studied medicinal plants against MDR bacteria. The tested plants could be a reservoir of molecules to fight against MDR bacterial infections.

Keywords: Cameroon, Gram-negative bacteria, Gram-positive bacteria, Medicinal plant, Multi-drug resistance, Antibacterial activity

Background

Infectious diseases caused by multidrug-resistant bacteria are growing steadily and are associated with a significant attributable mortality [1, 2]. The emergence of multi-drug resistant (MDR) phenotypes was first linked to nosocomial infections; but nowadays they are increasingly responsible for community infections and all pathogenic microorganisms are concerned. In Gram-negative bacteria, one of the mechanisms of resistance is the lowering of intracellular amount of antibacterial substances due to the presence of the resistance nodulation cell division (RND)-type efflux pumps. This phenomenon gives possibility to bacteria developing resistance to a wide range of antibiotics, as well as several biocides [3, 4]. Gram-positive bacteria are also a major cause of hospitalization; infections due to Staphylococcus aureus resistant to methicillin (MRSA) are a major health problem both in hospitals and community environments [5]. MRSA is responsible for 80461 severe infections and causing the death of 11,285 patients annually in the United States [6]. One of the possible ways to overcome this phenomenon of multi-resistance is the continual search for new antibacterial molecules active vis-à-vis of MDR bacteria. With regard to the broad diversity of their secondary metabolites, medicinal plants represent undeniable sources of antibacterial agents. According to WHO [7], 80 % of people in Africa have used medicinal plants for their health care; it is also estimated that among medicines sold worldwide, 30 % contain compounds derived from medicinal plants [8]. Several African medicinal plants previously investigated for biological potential showed good antibacterial activities. Some of them include Treculia obovoidea [9], Albizia adianthifolia Laportea ovalifolia [10], Alchornea cordifolia, Pennisetum purpureum [11]. In our continuous search of phytochemicals to combat MDR bacterial infections, we designed the present study to evaluate the antimicrobial potential of six Cameroonian medicinal plants namely Alstonia boonei, Catharanthus roseus, Ageratum conyzoides, Croton macrostachys, Cassia obtusifolia, and Paullinia pinnata vis-à-vis MDR Gram-negative and Gram-positive phenotypes.

Methods

Plant materials and extraction

Various parts of plant (Table 1) were collected from different regions in Cameroon during the month of February 2014. These include Alstonia boonei (leaves and bark), Catharanthus roseus (leaves and stem), Ageratum conyzoides (whole plant), Croton macrostachys (leaves), Cassia obtusifolia (whole plant), and Paullinia pinnata (leaves and stem). After drying, each part was powdered and soaked in methanol for 48 h at room temperature, and then filtered using Whatman filter paper N°1. The filtrate obtain were concentrated at 50 °C under reduce pressure in a vacuum to obtain each plant extract.

Table 1.

Information on plant used in the present study

Plant family/Plant sample - Herbarium voucher number Traditional use Part used in this study Potential active compounds characterized Previously screened activity
APOCYNACEAE/Alstonia boonei De Wild – 43368/HNC Fever, painful micturition, insomnia, chronic diarrhea, rheumatic pains, anti-venom (snake bites), malaria, diabetes, helminths, arthritis [28, 29]. Leaves, bark Echitamine, echitamidine, Voacangine, akuammidine, N- α-formylechitamidine, N- α-formyl-12-methoxyechitamidine [29]. Antimalarial, antioxidant, analgesic, anti-inflammatory, antipyretic [30–32].
APOCYNACEAE/Catharanthus roseus L. – 5689/HNC. Bleeding arresting, diabetes, fever, rheumatism, cancer [20, 33]. Leaves, stem Vincristine, vinblastine, benzoic acid, p-hydroxybenzoic acid, salicylic acid, 2,3-dihydroxybenzoic acid, 2,5-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid, 3,5-dihydroxybenzoic acid, gallic acid, vanillic acid, chlorogenic acid, kaemferol trisaccharides, Quercetin trisaccharides, Syringetin glycosides [20, 34]. Wound-healing, antimicrobial, hypoglycemic, antioxidant [18, 20, 33].
ASTERACEAE/Ageratum conyzoïdes Linn. – 19050/SFR-Cam Purgative, fever, ulcers, wound, mental, infectious diseases, headaches, anti-inflammatory, diarrhea [35, 36]. Whole plant β-caryophyllene, precocene I, friedelin, Lycopsamine, echinatine,β-sitosterol, stigmasterol, 5-methoxynobiletin, linderoflavone B, eupalestin, sabinene, α and β pinene, β-phellandrene, 1,8-cineole and limonene, ocimene, eugenol [35]. Antimicrobial, anticonvulsant, analgesic, anti-inflammatory, antipyretic, insecticidal, antioxidant, antiplasmodial, cytotoxic [35, 37, 38].
EUPHORBIACEAE/Croton macrostachys Hochst. – 40501/HNC Malaria, antidiabetic, purgative mastitis, wounds, gastrointestinal Complications [39–41]. Leaves Neoclerodan-5,10-en-19,6β;20,12-diolide; 3α,19-Dihydroxytrachylobane; 3α,18,19-Trihydroxytrachylobane, lupeol, lupenone, betulinic acid, 28-O-acetylbetulin, betulin, lupeol acetate, zeorin, benzoic acid, methyl gallate, methyl 2,4-dihydroxy-3,6-dimethylbenzoate, lichexanthone, β-sitosterol, and β-sitosterol palmitate, stigmasterol, botulin, crotepoxide [42, 43]. Antimicrobial, antimalarial, cytotoxic [38, 39, 41].
FABACEAE/Cassia obtusifolia L. – 39847/HNC Laxative, eye infections, diarrhea, urinary tract infections, gingivitis, fever, cough [25]. Whole plant aloe-emodin, 1-methylaurantio-obtusin-2-O-β-D-glucopyranoside, emodin, 1,2- dihydroxyanthraquinone, obtusin, chrysoobtusin, aurantioobtusin, gluco-obtusifolin, glucoaurantioobtusin, gluco-chryso-obtusin, 1-desmethylaurantio-obtusin, 1-desmethylaurantio-obtusin-2-O-β- D-glucopyranoside, 1-desmethylchryso-obtusin, 1-desmethyl-obtusin, aurantio-obtusin-6-O-β-D-glucopyranoside, alaternin-1-O-β-D-glucopyranoside, chrysoobtusin-2-O-β-D-glucopyranoside physicon-8-O-β-D-glucoside, obtusifolin, O-methyl-chrysophanol, emodin-1-O-β-gentio-bioside, chrysophanol-1-O-β-gentiobioside, physcion-8-O-β-gentiobioside, physcion-8-O-β-glucoside, chrysophanol-1-O-β-D-glucopyranosyl-(13)-β-D-glucopyranosyl-(1 → 6)-β-D-glucopyranoside, chrysophanic acid, physcion, questin, 1,3-dihydroxy-8-methylanthraquinone, chrysophanol- 10,10′-bianthrone, torosachrysone [44]. Antibacterial, antifungal, mosquito larvicidal activity, platelet antiaggregatory, neuroprotective [25, 45–47].
SAPINDACEAE/Paullinia pinnata L. – 10702/SRF-Cam Malaria, erectile dysfunction [24]. Leaves, stem Paullinoside A, paullinomides A and B, β-amyrin, 13β,17β-dihydroxy-28-norolean-12-ene, β-sitosterol glucopyranoside, 2-O-methyl-L-chiro-inositol, L-quebrachitol, β-sitosterol, friedelin, daucosterol, aridanin, lotoidoside [24, 48]. Antiparasitic, antimicrobial, cytotoxic [24, 38, 49].
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HNC Cameroon National Herbarium, SRF-Cam Société’ des Réserves Forestières du Cameroun

Preliminary phytochemical screenings

The presence of alkaloids, triterpenes, sterols, flavonoids, polyphenols and saponins were screened according to the common phytochemical methods described by Harborne [12].

Chemicals

Chloramphenicol and ciprofloxacin (Sigma–Aldrich, St. Quentin Fallavier, France) were used as reference antibiotics meanwhile p-Iodonitrotetrazolium chloride (INT) was used as microbial growth indicator.

Bacterial strains and culture media

The studied microorganisms included ATCC (American Type Culture Collection) and MDR clinical strains of Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa, Enterobacter aerogenes, Providencia stuartii, Klebsiella pneumoniae and Enterobacter cloacae) and Gram-positive bacteria (Staphyloccocus aureus). Their bacterial features are summarized in Table 2; they were maintained at 4 °C on McConkey agar and Mannitol Salt Agar (MSA) for Gram negative and Gram positive bacteria respectively, and sub-cultured on Mueller Hinton Agar (MHA) for 24 h before any test. Mueller Hinton Broth (MHB) was used for MIC and MBC determinations.

Table 2.

Bacterial strains used in this study and their features

Strains Characteristics References
Escherichia coli
 ATCC10536 Reference strain
 AG100 Wild-type E. coli K-12 [50]
 AG100A AG100 ΔacrAB::KANR
 AG100ATET ΔacrAB mutant AG100, with over-expressing acrF gene ; TETR [50–52]
 AG102 ΔacrAB mutant AG100, owing acrF gene markedly over-expressed; TETR [53, 54]
 MC4100 Wild type E. coli [55]
 W3110 Wild type E. coli [55, 56]
Enterobacter aerogenes
 ATCC13048 Reference strain
 CM64 CHLR resistant variant obtained from ATCC13048 over-expressing the AcrAB pump [57]
 EA3 Clinical MDR isolate; CHLR, NORR, OFXR, SPXR, MOXR, CFTR, ATMR, FEPR [58, 59]
 EA27 Clinical MDR isolate exhibiting energy-dependent norfloxacin and chloramphenicol efflux with KANR AMPR NALR STRR TETR [58, 59]
 EA289 KAN sensitive derivative of EA27 [60]
 EA294 EA289 acrA::KANR [60]
 EA298 EA 289 tolC::KANR [60]
Enterobacter cloacae
 ECCI69 Clinical MDR isolates, CHLR [61]
 BM67 Clinical MDR isolates, CHLR [61]
 BM47 Clinical MDR isolates, CHLR [61]
Klebsiella pneumoniae
 ATCC12296 Reference strain
 KP55 Clinical MDR isolate, TETR, AMPR, ATMR, CEFR [62]
 KP63 Clinical MDR isolate, TETR, CHLR, AMPR, ATMR [62]
 K24 AcrAB-TolC, Laboratory collection of UNR-MD1, University of Marseille, France [61]
 K2 AcrAB-TolC, Laboratory collection of UNR-MD1, University of Marseille, France [61]
Providencia stuartii
 NEA16 Clinical MDR isolate, AcrAB-TolC [63]
 ATCC29916 Clinical MDR isolate, AcrAB-TolC
 PS2636 Clinical MDR isolate, AcrAB-TolC
 PS299645 Clinical MDR isolate, AcrAB-TolC
Pseudemonas aeruginosa
 PA 01 Reference strain
 PA 124 MDR clinical isolate [64]
 S. aureus
 ATCC 25923 Reference strain
 MRSA 3 Clinical MDR isolate OFXR, KANR, TETR, ERMR [65]
 MRSA 4 Clinical MDR isolate OFXR, KANR, CHLR, CIPR
 MRSA 6 Clinical MDR isolate OFXR, FLXR, KANR, TETR, CIPR, IM/CSR
 MRSA 8 Clinical MDR isolate OFXR, FLXR, KANR, ERMR, CIPR, IM/CSR
 MRSA 11 Clinical MDR isolate OFXR, KANR, ERMR, CIPR, IM/CSR
 MRSA 12 Clinical MDR isolate OFXR, FLXR, KANR, ERMR, IM/CSR
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AMPR, ATMR, CEFR, CFTR, CHLR, CIPR, ERMR, FEPR, FLXR, IM/CSR, KANR, MOXR, OFXR, STRR, TETR, Resistance to ampicillin, aztreonam, cephalothin, cefadroxil, chloramphenicol, Ciprofloxacin, Erythromycin, cefepime, Flomoxef, Imipenem/Cilastatin sodium, kanamycin, moxalactam, streptomycin, and tetracycline; MDR multidrug resistant

INT colorimetric assay for MIC and MBC determinations

Minimal inhibitory concentrations (MIC) of different plant extracts were determined using broth microdilution method described by Kuete et al. [13] with some modifications [9]. Briefly, plant extracts, chloramphenicol and ciprofloxacin were dissolved in dimethylsufoxide (DMSO)-MHB (10:90) and 100 μL each solution was added to a 96 wells microplate containing MHB, then serially diluted two-fold, followed by adding of 100 μL of inoculum prepared in MHB. The microplate was sealed and incubated for 18 h at 37 °C. The final concentration of inoculum was 1.5 ×106 CFU/mL and less than 2.5 % for DMSO in each well; Wells containing DMSO 2.5 % and inoculums were used as negative control whereas chloramphenicol and ciprofloxacin consist of positive control. After 18 h incubation, 40 μL of INT (0.2 mg/mL) was added to each well and re-incubated for 30 min. MIC was defined as the lowest concentration of plant extract that inhibited bacterial growth.

The determination of MBC was made by introducing 150 μL of MHB in each well of 96 well plate. Then 50 μL of the well contents which did not show any growth after incubation during MIC assays was introduced in the aforesaid plate accordingly, and incubated at 37 °C for 48 h. The MBC was defined as the lowest concentration of plant extract, which did not produce a color change after addition of INT as described previously.

Results

Phytochemical composition

The results of qualitative analysis (Table 3) showed that plant extracts contain various phytochemical classes of secondary metabolites. Polyphenols, triterpenes and saponins were present in all plant extracts except those from Cassia obtusifolia, Catharanthus roseus leaves and stem respectively.

Table 3.

Extraction yields and phytochemical composition of the plant extracts

Plant extract (used part) Extraction yield (%) Phytochemicals groups
Alkaloids Triterpenes Sterols Flavonoids Polyphenols Saponins
A. boonei (leaves) 15.8 % - - + - + +
A. boonei (bark) 9.65 % + + + + + +
A. conyzoïdes (whole plant) 8.52 % - + + - - +
C. macrostachys (Leaves) 12.72 % - + + - + +
C. obtusifolia (whole plant) 7.11 % + + + + + +
C. roseus (leaves) 6.89 % + - + + + +
C. roseus (stem) 4.23 % + + + + + -
P. pinnata (leaves) 10.84 % - + + - + +
P. pinnata (stem) 5.47 % - + + - + +
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+: presence; −: absence

In vitro antibacterial effect of plant extract

The methanol extracts from different parts of plants were tested on 36 bacterial strains including 7 Gram-positive and 29 Gram-negative bacterial strains. As shown in Table 4, extracts from leaves of Alstonia bonnei, Paullinia pinnata and Catharanthus roseus displayed wide spectra of activity in comparison to those from bark and stems of the same plants. The various plant extracts (when they were active) had MIC between 64 and 1024 μg/mL. Leaves of Catharanthus roseus showed the best spectrum of activity, inhibiting the growth of 86.11 % (31/36) of the bacteria (24/29 Gram-negative bacteria and 7/7 Gram-positive bacteria). The leaves extract of Croton macrostachys also had an interesting activity (30/36; 83.33 %), followed by extract of the leaves of P. pinnata (29/36; 80.55 %) and the whole plant extract of A. conyzoides (25/36; 69.44 %). The lowest MIC value of 64 μg/mL was obtained with the Paullinia pinnata stems extract and Cassia obtusifolia extract against the strain of Staphylococcus aureus MRSA8. In general, analysis of results shows that MBCs were obtained in 3.35 % (7/209) of cases where plant extracts were active.

Table 4.

MIC and MBC (in bracket) of plant extracts and reference drugs

A. conyzoïdes (whole plant) A. boonei C. obtusifolia (whole plant) C. roseus C. macrostachys (leaves) P. pinnata Reference drugs
Leaves Bark Leaves Stem Leaves (Stem) Chloramphenicol
Escherichia coli
 ATCC8739 - 512 (−) - - 512 (−) - 512 (−) 1024 (−) - 2 (128)
 ATCC10536 256 (−) - - - 512 (−) 1024 (−) 256 (−) 128 (−) - <2 (64)
 AG100 1024 (−) - - 256 (1024) 1024 (−) - 1024 (−) 256 (−) 128 (−) 8 (128)
 AG100A 1024 (−) - - 512 (−) 128 (−) 256 (−) - 256 (−) 256 (−) <2 (128)
 AG100ATET 1024 (−) 512 (−) 1024 (−) - 1024 (−) - - - 512 (−) 32 (−)
 AG102 512 (−) 512 (−) 1024 (−) - - - 1024 (−) - 256 (−) 64 (−)
 MC4100 - - - - 512 (−) 512 (−) 256 (−) 256 (−) 1024 (−) 16 (−)
 W311O 1024 (−) - 128 (−) - 512 (−) - 256 (−) 1024 (−) - 2 (−)
Pseudomonas aeruginosa
 PA 01 - - - 256 (−) 512 (−) 256 (−) 256 (−) 256 (−) 1024 (−) 32 (−)
 PA 124 - - - - - - - - - 128 (−)
Enterobacter aerogenes
 ATCC13048 1024 (−) 512 (−) - 512 (−) - - 128 (−) - - 4 (32)
 EA-CM64 256 (−) - - 512 (−) 1024 (−) - 256 (−) 512 (−) 1024 (−) 256 (−)
 EA3 - - - - 256 (−) 1024 (−) 128 (−) - - 256 (−)
 EA27 256 (−) 512 (−) 512 (−) 512 (1024) 512 (−) 1024 (−) 512 (−) 512 (−) - 32 (−)
 EA289 512 (−) 1024 (−) 1024 (−) 256 (−) 512 (−) 1024 (−) 512 (−) 512 (−) 512 (−) 64 (−)
 EA298 1024 (−) - 1024 (−) 512 (−) 1024 (−) 1024 (−) 128 (−) 512 (−) 512 (−) 128
Providencia stuartii
 NEA16 1024 (−) 512 (−) 1024 (−) 1024 1024 (−) - 1024 (−) 1024 (−) 1024 (−) 32 (256)
 ATCC29916 512 (−) 512 (−) - - - - 256 (−) 1024 (−) - 16 (256)
 PS2636 256 (−) - - - - 256 (−) 256 (−) 256 (−) - 16 (256)
 PS299645 1024 (−) 512 (−) - - 256 (−) 512 (−) 512 (−) 512 (−) - 64 (−)
Klebsiella pneumoniae
 ATCC11296 512 (−) 512 (−) 1024 (−) 1024 (−) 1024 (−) 1024 (−) 512 (−) 1024 (−) - 8 (256)
 KP55 512 (−) 512 (−) - 256 (−) 512 (−) - 256 (−) 1024 (−) 256 (−) 32 (256)
 KP63 1024 (−) 1024 (−) - 1024 (−) 512 (−) - - 1024 (−) 1024 (−) 32 (−)
 K24 1024 (−) 512 (−) 1024 (−) 1024 (−) 1024 (−) - 512 (−) 512 (−) - 64 (256)
 K2 1024 (−) 256 (−) - 1024 (−) 512 (−) 512 (−) - - - 8 (256)
Enterobacter cloacae
 ECCI69 - 1024 (−) 1024 (−) 1024 (−) 1024 (−) - 1024 (−) 512 (−) 1024 (−) -
 BM47 - - - - 1024 (−) - 512 (−) 1024 (−) 1024 (−) 256 (−)
 BM67 512 (−) 512 (−) 1024 (−) 512 (−) 256 (−) - 256 (−) 1024 (−) - -
 BM94 1024 (−) 512 (−) 1024 (−) 512 (−) 512 (−) - 512 (−) 1024 (−) - 128 (−)
Staphyloccocus aureus Ciprofloxacin
 ATCC25923 512 (−) 256 (−) - 256 (1024) 512 (−) 1024 (−) 256 (−) 256 (−) 128 (1024) 2 (8)
 MRSA 3 - - - - 1024 (−) - - - - 32 (128)
 MRSA 4 256 (−) 256 (−) - 128 (1024) 512 (−) - 256 (−) 256 (−) 128 (512) 64 (128)
 MRSA 6 - 128 (−) - 256 (−) 1024 (−) 512 (−) 512 (−) 256 (−) 256 (−) 64 (128)
 MRSA 8 - 128 (−) - 64 (512) 128 (−) 1024 (−) 512 (−) 256 (−) 64 (512) 16 (64)
 MRSA 11 1024 (−) - - 512 (−) 1024 (−) 1024 (−) 1024 (−) 512 (−) 512 (−) 128 (256)
 MRSA 12 - 128 (−) - 256 (−) 1024 (−) 1024 (−) 512 (−) 256 (−) 256 (−) 32 (32)
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(−): MIC or MBC not detected up to 1024 μg/mL for plant extracts and 256 μg/mL for reference drugs

Discussion

Several classes of secondary metabolites such as alkaloids, triterpenes, sterols, flavonoids, polyphenols and saponins have been reported to have antibacterial properties [13–15]. Their presence in the studied plant extracts could explain the antibacterial effects of the tested samples. The need to find new molecules from medicinal plants with effective mechanisms of action against the multidrug-resistant phenotype is a necessity nowadays. All plants used in traditional medicine which have MIC values less than 8 mg/mL are considered active [16]. A plant extract has significant antibacterial activity if MIC is ˂100 μg/mL, moderate if its MIC is between 100 and 625 μg/mL and low when MIC is above 625 μg/mL [17]. Based on the above criteria, it can be deduced that all tested plants had antibacterial activity as MIC values below 8 mg/mL were obtained with each extract on at least one bacterial strain. MIC values above 625 μg/mL were obtained with extract from A. boonei bark against 2/36 (5.5 %) tested bacteria as well as with C. roseus stem extract against 6/36 (16.7 %) microorganisms tested, indicating that they rather displayed low antibacterial effects. Nonetheless, the activity obtained with the Paullinia pinnata stems extract and Cassia obtusifolia extract against the strain of Staphylococcus aureus MRSA8 (MIC value of 64 μg/mL) could be considered important. Moderate activity was obtained in many cases. In fact, MIC values ranged from 128 to 512 μg/mL were obtained with extract from A. conyzoides (whole plant) against 12/36 (33.3 %) tested bacteria, A. boonei leaves against 19/36 (52.8 %), C. obtusifolia (whole plant) against 17/36 (47.2 %), C. roseus leaves against 18/36 (50 %), C. macrostachys (leaves) against 25/36 (69.4 %), and P. pinnata stem and leaves against 13/36 (36.1 %) and 19/36 (52.8 %) respectively.

Though the antibacterial activities of some of the tested plants have already been reported, their effects against MDR phenotypes are being documented for the first time. The extract from the leaves of C. roseus had a broad antibacterial activity (31/36; 86.11 %); Nayak and Pereira [18] and Kamaraj et al. [19] reported the antibacterial activity of this plant extract on some sensitive bacteria. Several alkaloids were isolated from this plant [20, 21] and these compounds could also be responsible for the antibacterial activity of this plant [22]. MIC values obtained with extract of leaves of C. macrostachys are between 128 and 1024 μg/mL; Antibacterial compounds previously isolated from this plant include the triterpenoid, lupeol [23]. The extract of P. pinnata possessed a good activity (MIC of 64 μg/mL) against S. aureus MRSA8 while the extract from the leaves was active against 80.55 % (29/36) of the studied microorganisms. Lunga et al. [24] demonstrated the activity of this plant on strains of Salmonella sp. with a bacteriostatic effect, corroborating our findings. The extract of C. obtusifolia significantly inhibited the growth of S. aureus MRSA8 with MIC of 64 μg/mL, and was active on 22 of the 36 tested microorganisms. The activity obtained in this study is much better than that mentioned by Doughari et al. [25]. In fact, they obtained MIC of 2000 μg/mL and 1000 μg/mL on clinical isolate of S. aureus and P. aeruginosa respectively. This could be due to the difference of phytochemical composition as the environmental conditions influence the availability as well as the amounts of some secondary metabolites in the plant. One of the best suited secondary metabolite from this plant is emodin (anthraquinone) which possesses a good antibacterial activity against S. aureus [26]; this could explain the interesting activity observed vis-à-vis of MRSA in this study. The extract of A. conyzoides had a relatively low activity on all studied microorganisms. Nevertheless, MIC of 256 μg/mL vis-a-vis E. aerogenes EA-CM64 and EA27, P. stuartii PS2636, S. aureus MRSA 4 which are multi-drug resistant clinical strains were obtained; this could explain the use of this plant in traditional medicine. Leaves and bark extracts of A. bonnei had a moderate activity against Gram-negative bacteria whilst bark extract was not active against Gram-positive species; this is explained by the fact that some antimicrobial compounds have specific activity spectrum (narrow) and therefore will not be active on certain categories or certain species of microorganisms [27]. Though the overall activity of the tested plants can be considered moderate, the results of this study are interesting taking in account the fact that most of the tested bacterial strains were MDR phenotypes.

Conclusion

The present study demonstrates that plants studied and mostly C. macrostachys, C. roseus and P. pinnata contain phytochemicals with valuable antibacterial activities vis-à-vis multi-drug resistant phenotypes. They could be used in the management of bacterial infections including MDR phenotypes.

Acknowledgements

Authors are thankful to the Cameroon National Herbarium (Yaounde) for the plant identification. Authors are also thankful to UMR-MD1 (Mediterranean University, Marseille, France) and Dr Jean P. Dzoyem (University of Dschang) for providing some clinical bacteria.

Funding

No funding.

Availability of data and materials

The datasets supporting the conclusions of this article are presented in this main paper. Plant materials used in this study have been identified at the Cameroon National Herbarium where voucher specimens are deposited.

Authors’ contributions

IKV carried out the study; IKV and VK designed the experiments and wrote the manuscript; VK and VPB supervised the work; VK provided the bacterial strains; all authors read and approved the final manuscript.

Competing interests

The authors declare that they have no competing interests.

Consent for publication

Not applicable in this section.

Ethics approval and consent to participate

Not applicable in this section.

Abbreviations

A. conyzoides

Ageratum conyzoides

Alstonia boonei

Alstonia boonei

ATCC

American type culture collection

C. macrostachys

Croton macrostachys

C. roseus

Catharanthus roseus

Cassia obtusifolia

Cassia obtusifolia

CFU

Colony forming unit

DMSO

Dimethylsufoxide

E. aerogenes

Enterobacter aerogenes

E. cloacae

Enterobacter cloacae

E. coli

Escherichia coli

INT

p-Iodonitrotetrazolium chloride

K. pneumoniae

Klebsiella pneumoniae

MBC

Minimal bactericidal concentration

MDR

Multi-drug resistant

MHA

Mueller Hinton Agar

MHB

Mueller Hinton Broth

MIC

Minimum inhibitory concentration

MRSA

Methicillin resistant Staphylococcus aureus

MSA

Mannitol Salt Agar

P. aeruginosa

Pseudomonas aeruginosa

P. pinnata

Paullinia pinnata

P. stuartii

Providencia stuartii

RND

Resistance nodulation cell division

S. aureus

Staphyloccocus aureus

Contributor Information

Igor K. Voukeng, Email: tefogang@yahoo.fr

Veronique P. Beng, Email: v.penlap@yahoo.fr

Victor Kuete, Phone: (237) 677 35 59 27, Email: kuetevictor@yahoo.fr.

References

  • 1.Pop-Vicas A, Tacconelli E, Gravenstein S, Lu B, D’Agata EM. Influx of multidrug-resistant, gram-negative bacteria in the hospital setting and the role of elderly patients with bacterial bloodstream infection. Infect Control Hosp Epidemiol. 2009;30(4):325–31. doi: 10.1086/596608. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 2.Garnacho-Montero J, Corcia-Palomo Y, Amaya-Villar R, Martin-Villen L. How to treat VAP due to MDR pathogens in ICU patients. BMC Infect Dis. 2014;14:135. doi: 10.1186/1471-2334-14-135. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 3.Vargiu VA, Ruggerone P, Opperman JT, Nguyen TS, Nikaido H. Molecular Mechanism of MBX2319 inhibition of Escherichia coli AcrB multidrug efflux pump and comparison with other inhibitors. Antimicrob Agents Chemother. 2014;58(10):6224–34. doi: 10.1128/AAC.03283-14. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 4.Linhares I, Raposo T, Rodrigues A, Almeida A. Incidence and Diversity of Antimicrobial Multidrug Resistance Profiles of Uropathogenic Bacteria. Biomed Res Int. 2015;2015:354084. [DOI] [PMC free article] [PubMed]
  • 5.Rice BL. Antimicrobial Resistance in Gram-Positive Bacteria. Am J Med. 2006;119:11–9. doi: 10.1016/j.amjmed.2006.03.012. [DOI] [PubMed] [Google Scholar]
  • 6.CDC . Antibiotic resistance threats in the United States. Atlanta: U.S. Department of Health and Human Services, CDC; 2013. [Google Scholar]
  • 7.WHO. Traditional medicine. 2003. http://www.who.int/mediacentre/factsheets/2003/fs134/en/. Accessed 20 June 2016.
  • 8.FAO. Trade in medicinal plants. 2004. ftp://ftp.fao.org/docrep/fao/008/af285e/af285e00.pdf. Accessed 20 June 2016.
  • 9.Kuete V, Metuno R, Ngameni B, Tsafack AM, Ngandeu F, Fotso GW, et al. Antimicrobial activity of the methanolic extracts and compounds from Treculia obovoidea (Moraceae) J Ethnopharmacol. 2007;112:531–536. doi: 10.1016/j.jep.2007.04.010. [DOI] [PubMed] [Google Scholar]
  • 10.Tchinda FC, Voukeng KI, Penlap BV, Kuete V. Antibacterial activities of the methanol extracts of Albizia adianthifolia, Alchornea laxiflora, Laportea ovalifolia and three other Cameroonian plants against multi-drug resistant Gram-negative bacteria. Saudi J Biol Sci. 2016 doi: 10.1016/j.sjbs.2016.01.033. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 11.Mambe TF, Voukeng KI, Penlap BV, Kuete V. Antibacterial activities of methanol extracts from Alchornea cordifolia and four other Cameroonian plants against MDR phenotypes. J Taibah Univ Med Sci. 2016;11(2):121–127. [Google Scholar]
  • 12.Harborne JB. Phytochemical Methods. New York: Chapman and Hall; 1973. [Google Scholar]
  • 13.Kuete V, Ngameni B, Simo CC, Tankeu RK, Ngadjui BT, Meyer JJ, Lall N, Kuiate JR. Antimicrobial activity of the crude extracts and compounds from Ficus chlamydocarpa and Ficus cordata (Moraceae) J Ethnopharmacol. 2008;120(1):17–24. doi: 10.1016/j.jep.2008.07.026. [DOI] [PubMed] [Google Scholar]
  • 14.Cowan MM. Plant products as antimicrobial agents. Clin Microbiol Rev. 1999;12(4):564–82. doi: 10.1128/cmr.12.4.564. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 15.Mbaveng TA, Sandjo LP, Tankeo SB, Ndifor AR, Pantaleon A, Nagdjui TB, Kuete V. Antibacterial activity of nineteen selected natural products against multi-drug resistant Gram-negative phenotypes. SpringerPlus. 2015;4:823. doi: 10.1186/s40064-015-1645-8. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 16.Fabry W, Okemo PO, Ansorg R. Antibacterial activity of East African medicinal plants. J Ethnopharmacol. 1998;60:79–84. doi: 10.1016/S0378-8741(97)00128-1. [DOI] [PubMed] [Google Scholar]
  • 17.Kuete V. Potential of Cameroonian plants and derived-products against microbial infections: A review. Planta Med. 2010;76:1479–91. doi: 10.1055/s-0030-1250027. [DOI] [PubMed] [Google Scholar]
  • 18.Nayak BS, Pereira PLM. Catharanthus roseus flower extract has wound-healing activity in Sprague Dawley rats. BMC Complement Altern Med. 2006;6:41. doi: 10.1186/1472-6882-6-41. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 19.Kamaraj C, Rahuman AA, Siva C, Iyappan M, Kirthi VA. Evaluation of antibacterial activity of selected medicinal plant extracts from south India against human pathogens. Asian Pac J Trop Biomed. 2012;2(1):296–301. doi: 10.1016/S2222-1808(12)60169-8. [DOI] [Google Scholar]
  • 20.Goyal P, Khanna A, Chauhan A, Chauhan G, Kaushik P. In vitro evaluation of crude extracts of Catharanthus roseus for potential antibacterial activity. Int J Green Pharm. 2008;2(3):176–81. doi: 10.4103/0973-8258.42739. [DOI] [Google Scholar]
  • 21.Almagro L, Fernandez-Perez F, Pedreno MA. Indole alkaloids from Catharanthus roseus: bioproduction and their effect on human health. Molecules. 2015;20:2973–3000. doi: 10.3390/molecules20022973. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 22.Ali AMA, Lafta HA, Jabar HKS. Antibacterial activity of alkaloidal compound isolated from leaves of Catharanthus roseaus (L.) against multi-drug resistant strains. Res Pharm Biotech. 2014;5(2):13–21. [Google Scholar]
  • 23.Obey KJ, von Wright A, Orjala J, Kauhanen J, Tikkanen-Kaukanen C. Antimicrobial activity of Croton macrostachyus stem bark extracts against several human pathogenic bacteria. J Pathog. 2016;2016:1453428. [DOI] [PMC free article] [PubMed]
  • 24.Lunga KP, Tamokou JDD, Fodouop CSP, Kuiate JR, Tchoumboue J, Gatsing D. Antityphoid and radical scavenging properties of the methanol extracts and compounds from the aerial part of Paullinia pinnata. Springerplus. 2014;3:302. doi: 10.1186/2193-1801-3-302. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 25.Doughari JH, El-mahmood AM, Tyoyina I. Antimicrobial activity of leaf extracts of Senna obtusifolia (L) Afr J Pharm Pharmacol. 2008;2(1):7–13. [Google Scholar]
  • 26.Zhou L, Yun BY, Wang YJ, Xie MJ. Antibacterial mechanism of emodin on Staphylococcus aureus. Chin J Biochem Mol Biol. 2011;27(12):1156–60. [Google Scholar]
  • 27.Yamamoto T, Matsui H, Yamaji K, Takahashi T, Overby A, Nakamura M, Matsumoto A, Nonaka K, Sunazuka T, Omura S, Nakano H. Narrow-spectrum inhibitors targeting an alternative menaquinone biosynthetic pathway of Helicobacter pylori. J Infect Chemother. 2016 doi: 10.1016/j.jiac.2016.05.012. [DOI] [PubMed] [Google Scholar]
  • 28.Majekodunmi SO, Adegoke OA, Odeku OA. Formulation of the extract of the stem bark of Alstonia boonei as tablet dosage form. Trop J Pharm Res. 2008;7(2):987–94. doi: 10.4314/tjpr.v7i2.14683. [DOI] [Google Scholar]
  • 29.Adotey JPK, Adukpo GE, Boahen YO, Armah FA. A review of the ethnobotany and pharmacological importance of Alstonia boonei De wild (Apocynaceae) ISRN Pharmacol. 2012 doi: 10.5402/2012/587160. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 30.Bello IS, Oduola T, Adeosun OG, Omisore NOA, Raheem GO, Ademosun AA. Evaluation of Antimalarial Activity of Various Fractions of Morinda lucida Leaf Extract and Alstonia boonei stem Bark. Global J Pharmacol. 2009;3(3):163–65. [Google Scholar]
  • 31.Akinmoladun CA, Ibukun EO, Afor E, Akinrinlola BL, Onibon TR, Akinboboye AO, Obuotor EM, Farombi EO. Chemical constituents and antioxidant activity of Alstonia boonei. Afr J Biotechnol. 2007;6(10):1197–1201. [Google Scholar]
  • 32.Olajide OA, Awe OS, Makinde MJ, Ekhelar IA, Olusola A, Morebise O, Okpako TD. Studies on the anti-inflammatory, antipyretic and analgesic properties of Alstonia boonei stem bark. J Ethnopharmacol. 2000;71:179–86. doi: 10.1016/S0378-8741(99)00200-7. [DOI] [PubMed] [Google Scholar]
  • 33.Ferreres F, Pereira DM, Valentao P, Andrade PB, Seabra RM, Sottomayor M. New phenolic compounds and antioxidant potential of Catharanthus roseus. J Agric Food Chem. 2008;56(21):9967–9974. doi: 10.1021/jf8022723. [DOI] [PubMed] [Google Scholar]
  • 34.Mustafa RN, Verpoorte R. Phenolic compounds in Catharanthus roseus. Phytochem Rev. 2007;6:243–258. doi: 10.1007/s11101-006-9039-8. [DOI] [Google Scholar]
  • 35.Okunade AL. Ageratum conyzoides L. (Asteraceae) Fitoterapia. 2002;73(1):1–16. doi: 10.1016/S0367-326X(01)00364-1. [DOI] [PubMed] [Google Scholar]
  • 36.Lavergne R. Tisaneurs et Plantes Médicinales Indigènes de La Réunion. Saint Denis de La Réunion: Orphie; 2001. [Google Scholar]
  • 37.Jonville MC, Kodja H, Strasberg D, Pichette A, Ollivier E, Frederich M, Angenot L, Legault J. Antiplasmodial, anti-inflammatory and cytotoxic activities of various plant extracts from the Mascarene Archipelago. J Ethnopharmacol. 2011;136:525–31. doi: 10.1016/j.jep.2010.06.013. [DOI] [PubMed] [Google Scholar]
  • 38.Kuete V, Voukeng KI, Tsobou R, Mbaveng TA, Wiench B, Penlap BV, Efferth T. Cytotoxicity of Elaoephorbia drupifera and other Cameroonian medicinal plants against drug sensitive and multidrug resistant cancer cells. BMC Complement Altern Med. 2013;13:250. doi: 10.1186/1472-6882-13-250. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 39.Bantie L, Assefa S, Teklehaimanot T, Engidawork E. In vivo antimalarial activity of the crude leaf extract and solvent fractions of Croton Macrostachyus Hocsht. (Euphorbiaceae) against Plasmodium berghei in mice. BMC Complement Altern Med. 2014;14:79. doi: 10.1186/1472-6882-14-79. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 40.Salatino A, Salatino FML, Negri G. Traditional uses, Chemistry and Pharmacology of Croton species (Euphorbiaceae) J Braz Chem Soc. 2007;18(1):11–33. doi: 10.1590/S0103-50532007000100002. [DOI] [Google Scholar]
  • 41.Kalayou S, Haileselassie M, Gebre-Egziabher G, Tikue T, Sahle S, Taddele H, Ghezu M. In-vitro antimicrobial activity screening of some ethnoveterinary medicinal plants traditionally used against mastitis, wound and gastrointestinal tract complication in Tigray Region, Ethiopia. Asian Pac J Trop Biomed. 2012;2(7):516–22. doi: 10.1016/S2221-1691(12)60088-4. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 42.Kapingu MC, Guillaume D, Mbwambo HZ, Moshi JM, Uliso CF, Mahunnah RLA. Diterpenoids from the roots of Croton macrostachys. Phytochemistry. 2000;54(8):767–770. doi: 10.1016/S0031-9422(00)00166-7. [DOI] [PubMed] [Google Scholar]
  • 43.Tala FM, Tan NH, Ndontsa BL, Tane P. Triterpenoids and phenolic compounds from Croton macrostachyus. Biochem Syst Ecol. 2013;51:138–41. doi: 10.1016/j.bse.2013.08.001. [DOI] [Google Scholar]
  • 44.Dave H, Ledwani L. A review on anthraquinones isolated from Cassia species and their applications. Indian J Nat Prod Resour. 2012;3(3):291–319. [Google Scholar]
  • 45.Yang YC, Lim MY, Lee HS. Emodin isolated from Cassia obtusifolia (Leguminosae) seed shows larvicidal activity against three mosquito species. J Agric Food Chem. 2003;51(26):7629–31. doi: 10.1021/jf034727t. [DOI] [PubMed] [Google Scholar]
  • 46.Yun-Choi HS, Kim JH, Takido M. Potential inhibitors of platelet aggregation from plant sources, v. anthraquinones from seeds of Cassia obtusifolia and related compounds. J Nat Prod. 1990;53(3):630–33. doi: 10.1021/np50069a014. [DOI] [PubMed] [Google Scholar]
  • 47.Ju MS, Kim HG, Choi JG, Ryu JH, Hur J, Kim YJ, Oh MS. Cassiae semen, a seed of Cassia obtusifolia, has neuroprotective effects in Parkinson’s disease models. Food Chem Toxicol. 2010;48(8–9):2037–44. doi: 10.1016/j.fct.2010.05.002. [DOI] [PubMed] [Google Scholar]
  • 48.Miemanang R, Krohn K, Hussain H, Dongo E. Paullinoside A and paullinomide A: a new cerebroside and a new ceramide from leaves of Paullinia pinnata. Z Naturforsch. 2006;61:1123–27. doi: 10.1515/znb-2006-0910. [DOI] [Google Scholar]
  • 49.Okpekon T, Yolou S, Gleye C, Roblot F, Loiseau P, Bories C, Grellier P, Frappier F, Laurens A, Hocquemiller R. Antiparasitic activities of medicinal plants used in Ivory Coast. J Ethnopharmacol. 2004;90(1):91–7. doi: 10.1016/j.jep.2003.09.029. [DOI] [PubMed] [Google Scholar]
  • 50.Viveiros M, Jesus A, Brito M, Leandro C, Martins M, Ordway D, Molnar AM, Molnar J, Amaral L. Inducement and reversal of tetracycline resistance in Escherichia coli K-12 and expression of proton gradient-dependent multidrug efflux pump genes. Antimicrob Agents Chemother. 2005;49:3578–82. doi: 10.1128/AAC.49.8.3578-3582.2005. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 51.Kuete V, Ngameni B, Tangmouo JG, Bolla JM, Alibert-Franco S, Ngadjui BT, Pages JM. Efflux pumps are involved in the defense of Gram-negative bacteria against the natural products isobavachalcone and diospyrone. Antimicrob Agents Chemother. 2010;54:1749–52. doi: 10.1128/AAC.01533-09. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 52.Okusu H, Ma D, Nikaido H. AcrAB efflux pump plays a major role in the antibiotic resistance phenotype of Escherichia coli multiple-antibiotic-resistance (Mar) mutants. J Bacteriol. 1996;178:306–8. doi: 10.1128/jb.178.1.306-308.1996. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 53.Elkins CA, Mullis LB. Substrate competition studies using whole-cell accumulation assays with the major tripartite multidrug efflux pumps of Escherichia coli. Antimicrob Agents Chemother. 2007;51:923–9. doi: 10.1128/AAC.01048-06. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 54.Kuete V, Alibert-Franco S, Eyong KO, Ngameni B, Folefoc GN, Nguemeving JR, Tangmouo JG, Fotso GW, Komguem J, Ouahouo BM, Bolla JM, Chevalier J, Ngadjui BT, Nkengfack AE, Pages JM. Antibacterial activity of some natural products against bacteria expressing a multidrug-resistant phenotype. Int J Antimicrob Agents. 2011;37:156–61. doi: 10.1016/j.ijantimicag.2010.10.020. [DOI] [PubMed] [Google Scholar]
  • 55.Baglioni P, Bini L, Liberatori S, Pallini V, Marri L. Proteome analysis of Escherichia coli W3110 expressing an heterologous sigma factor. Proteomics. 2003;3:1060–65. doi: 10.1002/pmic.200300403. [DOI] [PubMed] [Google Scholar]
  • 56.Sar C, Mwenya B, Santoso B, Takaura K, Morikawa R, Isogai N, Asakura Y, Toride Y, Takahashi J. Effect of Escherichia coli wild type or its derivative with high nitrite reductase activity on in vitro ruminal methanogenesis and nitrate/nitrite reduction. J Anim Sci. 2005;83:644–52. doi: 10.2527/2005.833644x. [DOI] [PubMed] [Google Scholar]
  • 57.Ghisalberti D, Masi M, Pages JM, Chevalier J. Chloramphenicol and expression of multidrug efflux pump in Enterobacter aerogenes. Biochem Biophys Res Commun. 2005;328:1113–8. doi: 10.1016/j.bbrc.2005.01.069. [DOI] [PubMed] [Google Scholar]
  • 58.Mallea M, Chevalier J, Bornet C, Eyraud A, Davin-Regli A, Bollet C, Pages JM. Porin alteration and active efflux: two in vivo drug resistance strategies used by Enterobacter aerogenes. Microbiology. 1998;144:3003–9. doi: 10.1099/00221287-144-11-3003. [DOI] [PubMed] [Google Scholar]
  • 59.Mallea M, Mahamoud A, Chevalier J, Alibert-Franco S, Brouant P, Barbe J, Pages JM. Alkylaminoquinolines inhibit the bacterial antibiotic efflux pump in multidrug-resistant clinical isolates. Biochem J. 2003;376:801–5. doi: 10.1042/bj20030963. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 60.Pradel E, Pages JM. The AcrAB-TolC efflux pump contributes to multidrug resistance in the nosocomial pathogen Enterobacter aerogenes. Antimicrob Agents Chemother. 2002;46:2640–43. doi: 10.1128/AAC.46.8.2640-2643.2002. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 61.Voukeng IK, Kuete V. Epices Camerounaises et Bactéries multi-résistantes, Volume 1. 2013. [Google Scholar]
  • 62.Chevalier J, Pages JM, Eyraud A, Mallea M. Membrane permeability modifications are involved in antibiotic resistance in Klebsiella pneumoniae. Biochem Biophys Res Commun. 2000;274:496–9. doi: 10.1006/bbrc.2000.3159. [DOI] [PubMed] [Google Scholar]
  • 63.Tran QT, Mahendran KR, Hajjar E, Ceccarelli M, Davin-Regli A, Winterhalter M, Weingart H, Pages JM. Implication of porins in beta-lactam resistance of Providencia stuartii. J Biol Chem. 2010;285:32273–81. doi: 10.1074/jbc.M110.143305. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 64.Lorenzi V, Muselli A, Bernardini AF, Berti L, Pages JM, Amaral L, Bolla JM. Geraniol restores antibiotic activities against multidrug-resistant isolates from gram-negative species. Antimicrob Agents Chemother. 2009;53:2209–11. doi: 10.1128/AAC.00919-08. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 65.Paudel A, Hamamoto H, Kobayashi Y, Yokoshima S, Fukuyama T, Sekimizu K. Identification of novel deoxyribofuranosyl indole antimicrobial agents. J Antibiot. 2012;65:53–7. doi: 10.1038/ja.2011.110. [DOI] [PubMed] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Data Availability Statement

The datasets supporting the conclusions of this article are presented in this main paper. Plant materials used in this study have been identified at the Cameroon National Herbarium where voucher specimens are deposited.

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