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Phytochemistry, antioxidant and antibacterial activities of two Moroccan Teucrium polium L. subspecies: Preventive approach against nosocomial infections
⁎Corresponding author. yassinelbs@gmail.com (Yassine El Atki)
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Received: ,
Accepted: ,
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.
Peer review under responsibility of King Saud University.
Abstract
The aim of the present study was to determine the chemical composition and antioxidant activity of essential oils (EOs) from two Teucrium polium subspecies, to evaluate, also their antibacterial activities, against some nosocomial-bacteria. The phytochemical screening of essential oils was analyzed using gas chromatography-flame ionization detector (GC-FID) and gas chromatography-mass spectrometry analysis (GC-MS). The antibacterial activities were assessed by disc diffusion method and minimal inhibitory concentration (MIC), against Gram-negative bacteria (Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Citrobacter koseri and Acinetobacter baumannii) and Gram-positive bacteria Staphylococcus aureus. The antioxidant potential was evaluated in vitro by three assays, namely free radical scavenging activity against 1,1-diphenyl-2-picrylhydrzyl (DPPH), ferric reducing activity power (FRAP) and total antioxidant capacity. Twenty-six components were identified in the EO of Teucrium polium subsp. aurum representing. Its major component was Caryophyllene (19.13%) followed by γ-Muurolene (13.02%), τ-cadinol, (11.01%), α-Gurjunene (9.2%), Rosifoliol (8.79%), 3-Carene (7.04%). However, twenty two components were identified in the EO of T. polium subsp. polium. Its major components are 3-carene (16.49%), γ-Muurolene (14.03%), α-pinene (9.94%), α-phellandrene (6.93%) and Caryophyllene (7.51%). The antibacterial activity of both essential oils showed a higher activity against tested nosocomial bacteria especially against S. aureus and A. baumannii. The EO of T. polium subsp. aureum showed better antioxidant activity as measured by DPPH and FRAP assays with IC50 values of 3.7 ± 0.2 mg/ml and 2.31 ± 0.11 mg/ml, respectively. The total antioxidant capacity assay showed that T. polium subsp. aureum had a significant activity with value to 3308.27 mg equivalent to ascorbic acid/g of EO. The Moroccan T. polium essential oils could be exploited as an antimicrobial agent for the treatment of several infectious diseases caused by bacteria, especially, those who have developed resistance to conventional antibiotics.
Keywords
Teucrium polium
GC-MS
Nosocomial infections
Antibacterial
Antioxidant
- EOs
-
essential oils
- MIC
-
minimal inhibitory concentration
- T. polium
-
Teucrium polium
Abbreviations
1 Introduction
Nosocomial infections dominated by bacterial strains represent a real problem in our modern health care system, and they are characterized by high morbidity and mortality rates (Jenkins, 2017). In Morocco, The incidence of nosocomial infections, in the reanimation units is high and dominated by multi-drugs resistant bacteria (Maoulainine et al., 2014). Utilization of medicament is crucial for treating these infections, but it is also under the important selection pressure affecting many bacteria and those who have developed resistance. The world health organization (WHO, 2017), published a report listing the most dangerous multidrug-resistant bacteria to which a new antibiotic should be discovered urgently. This is the reason why natural alternatives were established in order to overcome the incidence of resistant bacteria (Rossiter et al., 2017). Several reports have indicated potent antimicrobial activity of essential oils, extracted from aromatic and medicinal plants, against various microorganisms (Gherraf et al., 2017; Siddique et al., 2020). Against to antibiotics, essential oils are composed of secondary metabolites therefore, the microorganisms cannot resist in mutant (Moussaoui and Alaoui, 2016). Among these essential oils, the potential antimicrobial of Teucrium species has been documented (Belmekki et al., 2014; Djabou et al., 2013; Ricci et al., 2005). The Teucrium polium L. (Lamiaceae) is distributed throughout Morocco with its subspecies, among which Teucrium polium L. subsp. Polium and Teucrium polium L. subsp. aurum (Navarro and El oualidi, 1997). In Morocco folk medicine, Teucrium polium (Germander) locally called ”Jaada”, it is used for the treatment of a variety of diseases, including digestive disorders, liver problems (Fakchich and Elachouri, 2014) inflammation, hypertension, fever, diabetes, rheumatism, parasitic diseases such as amoebicide (Henchiri et al., 2009). Numerous studies showed therapeutic properties of Teucrium polium such as, anti-inflammatory, anti-cancer (Menichini et al., 2009), antibacterial (Djabou et al., 2013; Stanković et al., 2017), antidiabetic (Tabatabaie and Yazdanparast, 2017), anti-spasmodic, anti-nociceptive (Parsaee and Shafiee-nick, 2006) and antioxidant effects (Khaled-Khodja et al., 2014). Study on chemical composition of essential oils from Algerian Teucrium polium subsp polium have been previously reported, α-pinene, Germacrene, γ-Cadinene, and α-Cadinol were identified as their major constituents (Djabou et al., 2012). However, to our knowledge, this is the first report on the phytochemical of T. polium subsp. aureum essential oil and, there has not been any study on the antioxidant and antibacterial activities of EOs from T. polium subsp. aureum and T. polium subsp. polium. Therefore, the main goal of the present work was to determine the phytochemicals and antioxidant potential of T. polium subsp. polium and T. polium subsp. aureum essential oils. Moreover to evaluate their antibacterial activity, against bacterial responsible for the nosocomial infections contracted at patients in the University Centre Hospital of Fez Morocco.
2 Materials and methods
2.1 Chemicals
Homologous series of n-alkanes (C8–C20), Butylated hydroxytoluene (BHT), 2,2-Diphenylpicrylhydrazyl radical (DPPH), ammonium molybdate, sodium phosphate, quercitin, vitamin C, iron III chloride (FeCL3), and 2,3,5-triphenyltetrazolium chloride (TTC) used in this study were purchased from Sigma-Aldrich (St. Louis, MO, USA). While potassium ferricyanide (K3Fe(CN)6), culture media and standard antibiotics were purchased from COGELAB (Morocco).
2.2 Selection and identification of plant material
Aerial parts of T. polium L. subsp. Polium and T. polium L. subsp. aureum were collected in April 2015 from the regions of Midelt (Morocco). They were identified by Professor Amina Bari, a botanist in the department of Biological Sciences, Faculty of Science, Sidi Mohammed Ben Abdellah University, Fez (Morocco). Plant material was dried for three weeks in the shade at room temperature. The samples dried were stored at 5 °C until the preparation of the plant essential oils.
2.3 Isolation of the essential oils
A portion (200 g) of the dried aerial parts was submitted for 3 h to water distillation, using a Clevenger-type apparatus, according to the method recommended by the European Pharmacopoeia (1975). Plant material (200 g) was distilled in 700 ml of water in a 2000 ml flask. The obtained essential oils were dried with anhydrous “sodium t sulfate” and stored in a refrigerator at 4–5 °C prior to analysis. Yields were calculated based on the dried weight of each sample.
2.4 Chemical analysis of the essential oils
2.4.1 Gas chromatography-flame ionization detector (CG-FID)
The isolated essential oils were diluted with hexane (dilution ratio 10:100), and 1 μl was sampled for the gas chromatographic analysis. Trace gas chromatograph (GC) (ULTRA S/N 20062969, Thermo Fischer), gas chromatograph equipped with HP-5MS non polar fused silica capillary column (60 m × 0.32 mm, film thickness 0.25 μm) was used. Operating conditions: oven temperature program from 50 °C (2 min) to 280 °C at 5 °C/min and the final temperature kept for 10 min; 2 “split mode” ratio 1:20; Nitrogen (N2)carrier gas, flow rate 1 ml/min; temperature of injector and detector (flame ionization detector) was fixed at 250 °C and 280 °C, respectively.
2.4.2 Gas chromatography-mass spectrometry analysis (GC-MS)
The Teucrium polium essential oils were analyzed run on a Thermo Fischer capillary gas chromatograph directly coupled to the mass spectrometer system (model GC ULTRA S/N 20062969; Polaris QS/N 210729), using an HP-5MS non polar fused silica capillary column (60 m × 0.32 mm, 0.25 mm film thickness). The operating condition of GC-MS oven temperature was kept as follows: initial temperature 40 °C for 2 min, programmed rate 2 °C/min up to final temperature 260 °C with isotherm for 10 min; injector temperature 250 °C. The helium was the carrier gas with a flow rate (1 ml/min). Essential oils were diluted in hexane with a dilution ratio of 10:100. The volume of the injected specimen was 1 µl of diluted oil, split injection technique; ionization energy 70 eV, in the electronic ionization mode; ion source temperature 200 °C, scan mass range of m/z 40–650 and interface line temperature 300 °C. Components characterization was made by determination of their retention indices (RI) relative to those of a homologous series of n-alkanes (C8–C20) (Fluka, Buchs/sg, Switzerland) and by matching their recorded mass spectra with those stored in the spectrometer database (NIST MS Library v. 2.0) and the bibliography (Adams, 2007).
2.5 Antibacterial activities of essential oils
2.5.1 Bacterial strains
In this study the antibacterial activity of T. polium L. subsp. Polium and T. polium L. subsp. aureum was tested against, Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative bacteria included Escherichia coli (E. coli), Klebsiella pneumoniae (K. pneumoniae), Pseudomonas aeruginosa (P. aeruginosa), Acinetobacter baumannii (A. baumannii) and Citrobacter koseri (C. koseri). All strains tested were isolated in a hospital environment from clinical patients in reanimation service (CHU, Morocco). The inoculum suspension was obtained by taking colonies from 24 h cultures. The colonies were suspended in sterile 0.9% aqueous solution of NaCl and shacked for 20 s. The density was adjusted to the turbidity of a 0.5 McFarland Standard (108 CFU/ml) (Mello et al., 2014).
2.5.2 Agar disc diffusion assay
The agar disc diffusion assay was determined in triplicate according to the experiment described by Furtado and Medeiros (1980). The suspensions of microorganisms (1–5 108 CFU/ml) were flood inoculated onto the surface of Mueller Hinton (MH) agar plates. Sterile 6 mm diameter filter discs (Whatman paper N° 3) were impregnated with 10 μl/disc of the compound and were put on to the surface of the inoculated Mueller Hinton agar. The plates were incubated at 37 °C for 18 h. Antibacterial effect was evaluated by measuring the inhibition zones against the tested bacterial strains. The standard drugs for comparison were the discs antibiogram of Imipenem (IMP) Vancomycyn (VA), Cefaclor (CEC), Nifrofurantoin (F), Kanamycin (K).
2.5.3 Determination of the minimum inhibitory concentration (MIC)
The minimum inhibitory concentration (MIC) was performed using a microdilution assay in 96-well plates according to the experiment of the National Committee for Clinical Laboratory Standards (NCCLS, 1999) with some modifications. The different concentrations of essential oils are prepared in a suspension containing 0.2% agar in sterile distilled water in order to disperse the compounds without adding solvent or detergent (Remmal et al., 1993). They are carried out by successive dilutions 1/2 ranging from 100 to 0.09 mg/ml. The concentrations obtained in the well were between 25 and 0.02 mg/ml. Bacterial suspensions were prepared in the same manner described previously and diluted in MH broth and plated in 96 well plates at a density of 1–5 × 106 CFU/ml. Finally, the plates were incubated at 37 °C for 18 h, bacterial growth was visually by adding to each well 20 μl of 2,3,5-triphenyltetrazolium chloride (TTC) aqueous solution (1%), with additional incubation for 1 h. MIC was defined as the lowest concentration that does not produce a red color (Mello et al., 2014).
2.6 In vitro antioxidant activities of essential oils
2.6.1 DPPH radical scavenging activity
The DPPH method was introduced 50 years ago by Blois (1958). The ability of the essential oil to scavenge the DPPH radical was measured using the method described by Wu et al. (2003). 0.1 ml of various concentrations of the essential oil or standard was added to 1.5 ml of the ethanolic solution containing 0.1 mmol of DPPH (2, 2-diphenyl-1 picrylhydrazyl). The absorbance of the mixture was measured at 517 nm by a spectrophotometer (Jasco V-530) after 30 min of incubation time at room temperature in dark. The percentage inhibition was calculated by the following equation: where A0 is the absorbance of the negative control, and AS is the absorbance of the sample. BHT served as a positive control. The IC50 values were calculated as the concentration of causing a 50% inhibition of DPPH radical.
2.6.2 Reducing power capacity (FRAP)
The reducing power capacity of the tested oils was determined in accordance with the procedure of Oyaizu (1986). 200 µl of the essential oils were mixed with 500 µl of phosphate buffer (0.2 M, pH 6.6) and 500 µl of potassium ferricyanide [K3 Fe(CN)6] 1%. The obtained solution was incubated at 50 °C for 20 min. The mixture was acidified with 500 µl of trichloracetic acid (TCA) 10%. Which was then centrifuged at 3000 rpm for 10 min. The upper layer of the solution (2.5 ml) was mixed with 500 µl of distilled water and 100 µl of FeCl3 (0.1%), and the absorbance was measured at 700 nm (Jasco v-530). Quercetin and BHT were used as a standard. The results were expressed as IC50 (mg/ml). IC50 (concentration corresponding 0.5 of absorbance) was calculated by plotting absorbance against the corresponding concentration.
2.6.3 Total antioxidant capacity
The assay was based on the reduction of Mo (VI) to Mo (V) and subsequent formation of a green phosphate Mo (V) complex in acid pH (Prieto et al., 1999). A total volume of 25 µl of essential oil was added to 1 ml of reagent solution (0.6 mol/L sulphuric acid, 28 mmol/L sodium phosphate and 4 mmol/L ammonium molybdate). The mixtures were incubated at 95 °C for 90 min and then cooled to room temperature. The absorbance was measured at 695 nm (Jasco v-530). The total antioxidant activity was expressed as the number of equivalence of ascorbic acid (mg AAE/g EO).
2.7 Statistical analysis
The mean values, ±standard deviations were calculated by using GraphPad Prism 5 (Microsoft Software). The results were compared by one-way ANOVA followed by Tukey-test, using the same software. Differences at P < 0.05 were considered to be significant.
3 Result and discussion
3.1 Essential oils yield
The essential oils obtained from the aerial parts of T. polium subsp. aureum and T. polium subsp. polium were transparent yellow in color, yielded 0.9% and 0.75%, respectively. This yield is higher than that of T. polium studied in Algeria (0.27%) (Belmekki et al., 2014) and less than that of Saudi Arabia T. polium (1.65%) (Al-Ghamdi and Al-ghamdia, 2014).
3.2 Essential oils chemical composition
The chemical composition of essential oils from two Teucrium species was analyzed by GC-FID and GC–MS techniques, and their chromatographic profiles were summarized in Figs. 1 and 2. Constituents of EOs are listed in order of their elution on the HP-5MS column (Table 1). Twenty six components were found in the essential oil of Teucrium polium subsp. aurum representing 93.16% of the total oil. Its major component was Caryophyllene (19.13%) followed by γ-Muurolene (13.02%), τ-cadinol, (11.01%), α-Gurjunene (9.2%), Rosifoliol (8.79%), 3-Carene (7.04%), with a prevalence of Sesquiterpene hydrocarbons (64.11%). However, Twenty two components were identified in the oil of T. polium subsp. polium (94.49% of total oil). Its major components are 3-carene (16.49%), γ-Muurolene (14.03%), α-pinene (9.94%), α-phellandrene (6.93%) and Caryophyllene (7.51%). Sesquiterpene hydrocarbons (54.5%) and Monoterpene hydrocarbons (38.23%) constituted the most abundant fraction of this oil. Notice that certain components exist in the T. polium subsp. aureum EO (α-terpenyl acetate, β-Cubebene, Aristolene, Valencene, Cubenol and Rosifoliol) but, are absent in the T. polium subsp. polium EO. Similarly; α-phelandrene, Aromadendrene, and Ledol; exist in the essential oil of the T. polium subsp. polium but not in the oil of the T. polium subsp. aureum. Moreover, To our knowledge only one study has been reported on the phytochemical of T. polium subsp. polium that demonstrated that Germacene (14.8%) β-pinene (16.6%) and α-pinene (7.2%) are its main components (Djabou et al., 2012). However, other studies have determined the chemical composition of T. polium but they did not specify its subspecies. Cozzani et al. (2005) found that the main components of T. polium EO were α-pinene (28.8%), β-pinene (7.2%) and p-cymene (7.0%). Germacrene (25.81%), bicyclogermacrene (13%), ß-pinene (11.69%) were found to be the main components in T. polium EO (Belmekki et al, 2014). In Karpathos Island, Carvacrol (10.1%), Germacrene (3.1%), and γ-Cadinene (2.5%) are the major constituents of T. polium EO (Menichini et al., 2012). Furthermore, the major constituents of T. polium oil from Saudi Arabia were α-Cadinol (5.93%) and β –pinene, β-gurjurene, and α-pinene (Al-Ghamdi and Al-ghamdia, 2014). These differences in the composition of essential oils can be dependent on different factors, including the location of the plant species and method of extraction of the essential oil (Zhigzhitzhapova et al., 2014). In other hand, gas chromatography-flame ionization detector (GC-FID) and gas chromatography-mass spectrometry analysis (GC-MS) have been extensively used in the determination of EOs composition, because of their advantages such as high efficiency and speed properties (Shabir, 2005). Moreover, owing to the widespread use of GC in routine essential oils analysis, it is necessary that good GC methods are developed and that these are thoroughly validated (Sousa and Brancalion, 2011). For example, Wang et al. (2014) developed an automatic gas chromatograph system equipped with a mass spectrometer and a flame ionization detector (GC-MS/FID) for online measurements of volatile compounds in ambient air, such as C2–C12 hydrocarbons, C3–C6 carbonyls, halocarbons, and alkyl nitrates (Wang et al., 2014).
Chromatographic profile by GC-MS of T. polium subsp. polium.
Chromatographic profile by GC-MS of T. polium subsp. aurum.
Compounds
RI
T. polium subsp. aureum area (%)
T. polium subsp. polium area (%)
α-Thujene
803
0.3
0.67
α-pinene
809
3.5
9.94
γ-Terpinene
824
0.5
1.01
b-Myrcene
971
0.59
0.12
α-phelandrene
993
–
6.93
3-Carene
1007
7.04
16.49
Trans-sabinol
1109
0.4
0.62
Myrtenol
1194
3.02
1.11
α-Terpinyl acetate
1230
1
–
Thymol
1244
0.4
0.57
β-Cubebene
1283
1.3
–
Aromadendrene
1343
–
1.3
Valencene
1391
0.56
–
Caryophyllene
1445
19.13
7.51
Aristolene
1416
0.9
–
Alloaromadendrene
1437
5.01
3.2
α-Himachalene
1452
1.32
5.56
β-elemene
1463
–
0.2
γ-selinene
1473
0.3
–
γ-Muurolene
1478
13.02
14.03
α-Gurjunene
1492
9.2
6.54
β-Eudesmol
1508
1.05
–
Ledol
1525
–
2.08
Germacrene-D-4-ol
1543
2.36
3.93
Spathulenol
1551
1.2
0.73
Caryophyllene oxid
1574
0.24
0.32
Cubenol
1583
0.7
–
τ-Cadinol
1595
11.01
5.1
Muurolol
1642
–
6.53
Rosifoliol
1654
8.79
–
Benzyl benzouate
1720
0.32
–
Monoterpene hydrocarbons
11.93
38.23
Oxygenated monoterpenes
3.82
2.3
Sesquiterpene hydrocarbons
64.11
54.3
Oxygenated sesquiterpenes
12.3
9.66
Total (%)
93.16
94.49
3.3 Antibacterial activities of essential oils
The antibacterial activities of essential oils from T. polium subsp. polium and T. polium subsp. aureum were studied, for the first time, using agar disk diffusion test and minimal inhibitory concentration (MIC) methods against six bacteria strains (E. coli, K. pneumonia, P. aeruginosa S. aureus, C. koseri and A. Boumanii) responsible for nosocomial infections in Centre Hospital University of Fez, Morocco. Table 2 revealed that the tested EOs showed a wide antibacterial spectrum, against tested strains with the inhibition zone diameters varying from 8 to 23 mm, we notice that T. polium subsp. aureum and T. polium subsp. polium EOs had similar and comparative activities. Interestingly, these diameters were sometimes higher than those obtained with standard antibiotics used as controls. The gram-positive S. aureus and the Gram-negative A. baumannii were the most sensitive of the strains tested to both oil samples. However, these EOs showed a low activity against the Gram-negative P. aeruginosa. Table 3 summarized the MIC values of the essential oils against the tested strains. Oils from T. polium subsp. aureum and T. polium subsp. polium exhibited significant antimicrobial activity against S. aureus (MIC 0.17 mg/ml) and K. pneumonia (MIC 1.4 and 0.7 mg/ml). Compared to C. koseri (MIC 2.81 mg/ml) and A. baumannii (MIC 2.81 and MIC > 1.4 mg/ml), respectively. While, these EOs have low activity against P. aeruginosa, which was only inhibited at high concentration (5.62 mg/ml). Generally, the correlation between the antimicrobial activity of the EOs and their chemical composition suggests that the activity of the EOs could be attributed to the presence of high concentrations of the major compounds (Siddique et al., 2020). However, many reports have suggested that the synergistic or antagonistic action of the major and minor components from the EOs should be taken into consideration to explain their antimicrobial proprieties (Cutillas et al., 2018; Fadli et al., 2012). In the present study, we found that S. aureus appears to be more sensitive to both essential oils. It has been shown that Gram-negative bacteria are less sensitive than Gram-positive bacteria to the essential oils (Ruiz-Navajas et al., 2012; Tenore et al., 2011). This difference in susceptibility could be explained by the structure of cell envelope Gram-negative bacteria possess an outer lipopolysaccharides membrane, delineating the periplasmic space with the cytoplasmic membrane that can limit diffusion of hydrophobic compounds. Without this membrane, the cell wall from Gram-positive group can be permeated more easily and external agents can alter the cytoplasmic membrane (Ruiz-Navajas et al., 2012; Tenore et al., 2011). As we showed, P. aeruginosa was the most highly resistant to both essential oils and to the antibiotics. Numerous studies had shown that P. aeruginosa is the most resistant to EOs (Kamari et al., 2018; El Atki et al., 2019; Jalal et al., 2015). It reported that the resistance of P. aeruginosa may be due to the structure of its outer membrane particularly impermeable to EO and related to the action of efflux mechanisms, protecting the bacteria against the action of EO molecules (Utchariyakiat et al., 2016; Tenore et al., 2011). According to Fertout-Mouri et al. (2017), the Gram-positive microorganisms were found to be more sensitive to essential oils from T. polium than Gram-negative bacteria. Antimicrobial activity of essential oil from T. polium has been investigated against five multi-drug resistant ATCC bacteria (P. aeruginosa, E. coli, S. aureus, Enterococcus faecalis, and Bacillus cereus). The results showed that T. polium oil is active against all strains except for P. aeruginosa (Belmekki et al., 2014). Inhibition zone includes diameter of disk (6 mm); NI: No inhibition; NT: Not tested; IMP: Imipenem; VA: Vancomycyn; CEF: Cefaclor; F: Nifrofurantoin; K: Kanamycin.
Bacterial species
Inhibition zone (mm)
Essential oils
Antibiotics
T. polium subsp. polium
T. polium subsp. aureum
VA
F
CEC
IMP
K
K. pneumoniae
13 ± 0.5
11 ± 0.3
NI
22
NI
25
24
P. aeruginosa
8 ± 0.4
8 ± 0.2
13
20
12
NT
S. aureus
23 ± 1.4
21 ± 1
14
20
14
39
17
A. Boumanii
15 ± 0.8
20 ± 0.6
18
15
NI
NT
NT
C. koseri
12 ± 0.1
10 ± 0.01
16
16
9
12
15
E. coli
10 ± 0.5
11 ± 0.6
NI
19
NI
28
17
Bacterial species
T. polium subsp. polium
T. polium subsp. aureum
K. pneumoniae
0.7
1.4
P. aeruginosa
5. 62
5.62
S. aureus
0.17
0.17
A. baumannii
2.81
1.4
C. koseri
2.81
2.81
E. coli
5.62
2.81
3.4 Antioxidant activities of essential oils
DPPH test, FRAP, and phosphomolybdenum assays were used to evaluate antioxidant activities of Teucrium polium oils. The free radical scavenging activity of investigating essential oils was evaluated by the DPPH test. DPPH• is a stable free radical that can receive hydrogen or electron from an antioxidant to become a stable molecule. As depicted in Fig. 3, the both essential from T. polium oils presented a potent antiradical effect in a concentration dependent manner. The concentrations of the tested samples needed to remove 50% of the DPPH (IC50) are calculated and presented in Table 4. The results indicate that the T. polium subsp. aureum showed the higher DPPH radical scavenging activity than T. polium subsp. polium with IC50 values of 3.7 and 7.2 mg/ml, respectively. But was significantly (p < 0.001) lower than that of pure reference antioxidant BHT (0.12 mg/ml). Values are giving as mean ± SD (n = 3). In each column, different letters are significantly different by the Tukey-test (P < 0.05).
DPPH free radical scavenging activity of T. polium subsp aureum and T. polium subsp polium. BHT was used as reference.
DPPH (mg/ml)
FRAP (mg/ml)
Total antioxidant capacity (mg AAE/g EO)
T. aureum
3.7 ± 0.2b
2.31 ± 0.11b
1774.42 ± 87b
T. polium
7.2 ± 0.55a
3.5 ± 0 .5a
3308.27 ± 100a
BHT
0.12 ± 0.01c
0.1 ± 0.01c
540.62 ± 40c
Quercetin
–
0.03 ± 0.00d
512.70 ± 15c
The reductive capacity is generally associated with the presence of antioxidant agents which exert their effect by breaking the free radical chains via hydrogen atom donation (Blažeković et al., 2010). Therefore, the ferric reducing power of investigating essential oils was evaluated by the FRAP assay. The reducing power assay is often used to evaluate the ability of an antioxidant to transform the Fe3+ to Fe2+. Fig. 4 showed the reducing power of different concentrations of two essential oil T. polium subspecies in comparison to quercetin and BHT. The results demonstrated that the both essential oils possessed the ability to reduce Fe3+, and their reducing power increased with a concentration. T. polium subsp. aurum had a significant ferric reducing power than T. polium subsp. polium with IC50 values of 2.31 mg/ml and 3.5 mg/ml, respectively, but it was still significantly (p < 0.001) less than that of the synthetic antioxidants quercetin and BHT (Table 4).
Reducing power of T. polium subsp aureum and T. polium subsp polium. Quercetin and BHT were used as references.
Total antioxidant capacity of investigating T. polium essential oils, and reference antioxidant (quercitin and BHT) was determined by phosphomolybdenum method, which is based on the reduction of Mo (VI) to Mo (V) in the presence of an antioxidant (Prieto et al., 1999). The results expressed as ascorbic acid equivalents (mgAAE/g EO) are given in Table 4. The total antioxidant capacity of T. polium subsp. polium was significantly better in comparison to T. polium subsp. aureum, BHT and quercetin with values of 30308.27; 1774.42; 540.62 and 512.70 mgAAE/g EO, respectively.
According to Abdillah et al (2015), An antioxidant agent is considered to be active against free radicals if IC50 less than 5 mg/ml (Abdillah et al., 2015). The EO studied of T. polium subsp. aureum have IC50 < 5 mg/ml, therefore this EO is a possible good source of antioxidant compounds. The poor activity of the T. polium EO can be attributed to the weak ability of their main components to scavenge DPPH free radicals (Aazza et al., 2011). Moreover, previous studies showed significant free radical Scavenging activity of EOs from some Teucrium species (Ricci et al., 2005; Saroglou et al., 2007). It is noteworthy that the antioxidant activities of the two subspecies of T. polium essential oils are reported here for the first time.
4 Conclusion
This study is the first characterization of the chemical composition, antioxidant and antibacterial (against nosocomial infections) activities of two wild Moroccan T. polium subsp essential oils. Our results demonstrated that the major constituents are different in the essential oils of two subspecies. Moreover, the remarkable antioxidant effect and strong inhibitory activity against nosocomial-bacteria of T. polium essential oils suggest their possible use as a natural antibacterial drug for bacteria causing nosocomial infections in the intensive care rooms.
Acknowledgement
The authors wish to thank the Regional Center of Interface, University Sidi Mohamed Ben Abdellah, Morocco, for providing GC-MS facilities. Special thanks go to Professor Amina Bari (Sidi Mohammed Ben Abdellah University, Morocco) for the identification of the plants.
Funding sources
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Contribution of authors
We declare that this work was done by the authors named in this article, A. Abdellaoui conceived and designed the study. Y. El atki and I. Aouam: carried out the laboratory work, collected and analyzed the data and writing the manuscript. F. El kamari and A. Taroq: supervised the work and assisted in data analysis, B. Oumokhtar who isolated and identified the nosocomial bacteria. While B. Lyoussi revised and corrected the manuscript. The manuscript was proof-read by all the authors and approved for publication.
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