A review on medicinal plant extracts and their active ingredients against methicillin-resistant and methicillin-sensitive Staphylococcus aureus

Introduction Staphylococcus aureus is a gram-positive bacterium colonized on the skin, and present in the nose of 25% to 30% of healthy people (1). In general, the nose, armpit and groin before the invasive infection with S. aureus are sites where the bacteria are colonized (2). A broad spectrum of infections, ranging from minor skin infections to postoperative wound infections are caused by S. aureus (3). This bacterium is one of leading human pathogens that has high resistance to antibiotics and is the main source of hospital-acquired and community-acquired infections (4,5). Nosocomial infections with S. aureus, in particular methicillin-resistant S. aureus (MRSA), are of the major causes of hospitalization, which imposes a high economic burden on the patients and the hospital (6). The MRSA is one of the opportunistic pathogens considered to be a serious threat to public health (7). The bacterium was described for the medical community through a prominent article published for the first time in a British Medical Journal (8). After the introduction of http://www.herbmedpharmacol.com doi: 10.15171/jhp.2019.xx


Introduction
Staphylococcus aureus is a gram-positive bacterium colonized on the skin, and present in the nose of 25% to 30% of healthy people (1).In general, the nose, armpit and groin before the invasive infection with S. aureus are sites where the bacteria are colonized (2).A broad spectrum of infections, ranging from minor skin infections to postoperative wound infections are caused by S. aureus (3).This bacterium is one of leading human pathogens that has high resistance to antibiotics and is the main source of hospital-acquired and community-acquired infections (4,5).Nosocomial infections with S. aureus, in particular methicillin-resistant S. aureus (MRSA), are of the major causes of hospitalization, which imposes a high economic burden on the patients and the hospital (6).The MRSA is one of the opportunistic pathogens considered to be a serious threat to public health (7).The bacterium was described for the medical community through a prominent article published for the first time in a British Medical Journal (8).After the introduction of methicillin to the medical arena in 1960, the MRSA was first identified in Europe.Natural resistant strains have been isolated without the use of methicillin or related agents in some countries (9).Methicillin resistance occurs due to the presence of the mecA gene encoding PBP2a (penicillin-binding protein 2a) molecule that has a slight affinity for binding to β-lactam antibiotics.The PBPs are trans-peptidases that catalyze the interaction between the peptide bridges of the bacterial cell wall.The mutation in this molecule causes antibiotic resistance of the bacterium (10).
A similar PBP2a has been described recently, encoding by mecC, and is homogeneous by 70% with mecA (11).The SCC (Staphylococcal cassette chromosomes) elements have been so far described as the only carrier for the mecA gene.These elements are classified into different types according to the type of recombinases they carry and their overall genetic composition.Coagulase-negative staphylococci with mecA are of the potential reservoir of these elements (12).The first strain of community-acquired MRSA (CA-MRSA) was reported in 1990.In recent years, it has been unclear the distribution of hospital-acquired MRSA (HA-MRSA) and CA-MRSA strains.Both strains are endemic in hospitals in many areas.The changes in the MRSA evolution have made these bacteria a serious threat to public health.The CA-MRSA develops a series of skin and soft tissue infections and sometimes severe infections (3,(13)(14).Indiscriminate administration of antibiotics is one of the causes of antibiotic resistance.The high level of antibiotic resistance and the presence of SCC mec types indicate that infections caused by these strains require more advanced care and also newer antibiotics (15).The antibiotic resistance is the biggest challenge for the medical area in the treatment of infectious diseases.The resistance has been documented not only against natural and semi-synthetic antibiotics, but also against fully synthesized compounds (such as fluoroquinolones) or antibiotics that do not even penetrate through the cells (such as vancomycin) (16).This study was aimed to review the antibacterial activity of different medicinal plants and the effects of their active ingredients on MRSA and MSSA, and to clarify the pathway to further studies in this regard.

Medicinal plants
Herbal medicines embrace a wide range of practices and therapies outside the realm of traditional Western medicine.Although herbal medicines are not risk free, they can still be safer than synthetic drugs.The potential benefits of herbal medicines include high acceptance by patients, effectiveness, relative safety and relatively low costs (17).Due to the increasing use of herbal medicines around the world, their safety has often become a medical issue (18).Many consumers are demanding food that is free of harmful and chemically synthetic materials, including food antimicrobial preservatives.As a result, the passion for natural antimicrobial substances has been increased as potential alternative to commonly used antimicrobial agents to increase half-life and control the food pathogens (19).The complementary and alternative medicine practices are increasingly being employed to detect or treat allergic diseases, and numerous studies have been reported on the benefits of this type of medication (20).Conventional drugs usually provide antibiotic treatment for bacterial infections, but the problem of increasing antibiotic resistance reveals the need for new therapies.Over the past few years, the use of natural ingredients has attracted further attention to promote human and animal health.Hence, increased antibiotic resistance has encouraged healthcare providers to be in the wake of alternatives, including botanical and herbal medicines to manage the invasive microorganisms (21,22).
Huge consideration has been directed to determine the antimicrobial activity of the plant extracts in traditional medicine, essential oils or other isolated ingredients, such as alkaloids, flavonoids, diterpenes, triterpenes or naphthoquinones, sesquiterpene lactones, and the like.Some of these compounds have been separated after detecting the antimicrobial activity of the plant (23).The flavonoids are compounds present in photosynthetic cells and commonly found in fruits, vegetables, stems, seeds, flowers, and so on.Many studies have been conducted to identify the antibacterial mechanisms of the flavonoids.For example, quercetin activity is partly responsible for inhibiting DNA gyrase.It has been observed that sophoraflavone G and epigallocatechin gallate hamper the energy metabolism of membrane cell function and licochalcones A and C (24).Flavonostilbenes have shown special antibacterial and antibiofilm activity against Staphylococcus epidermidis with minimum inhibitory concentration (MIC) values of 3.1 to 12.5 μg/ mL (25).Phenolic acids exist in our various diets such as foods made thanks to Fungi, which owing to their biological properties have been widely investigated so that there is evidence of their role in disease prevention.However, these compounds are metabolized in vivo, circulating as glucuronidated, sulfated and methylated metabolites and indicating higher or lower biological activity (26).The essential oils are complex compounds among the various types of volatile molecules such as terpenoids, aromatic compounds derived from phenols and aliphatic compounds, which have found many fans in pharmaceutical, health, cosmetic, agriculture and food industries (27).The essential oils have been used since the middle ages as bactericides, virucides, fungicides, disinfectants, insecticides and other purposes such as analgesics, sedatives, anti-inflammatory agents, spasmolytics and local anesthetics (28).Terpenoids and phenylpropanoids are the main components of essential oils that provide their biological properties (29).Sesquiterpenoids, and especially sesquiterpene lactones, from family Asteraceae play a pivotal role in human health as part of a balanced diet and pharmaceutical agents.Some sesquiterpene lactones have antimicrobial properties and can impair fungal and bacterial cell wall (30).

The active ingredients of medicinal plants against S. aureus
This article attempts to highlight the findings of previous studies regarding the antimicrobial effects of various herbal compounds on bacteria, including S. aureus and MRSA, in order to clarify the effects of medicinal plants on these bacteria.A comprehensive description of medicinal plants with antibacterial activities is presented bellow and a summary of them are listed in Table 1.

Family Asteraceae
The plants in family Asteraceae are of great interest owing to compounds such as flavonoids, saponins, steroids, alkaloids and glycosides.The active compounds in this family are sesquiterpene lactones, which are key secondary metabolites responsible for the antibacterial activity of this family (52,53).Xanthium strumarium extract showed significant effect on MSSA (25 mm) and MRSA (20 mm), which had more effect on MSSA.The results exhibited correlation of dose and sensitivity between the plant extract concentrations and bacterial growth inhibition.The antibacterial activity of this plant may be due to the presence of phenolic acids, flavonoids, tannins and terpenoids in the methanolic extracts (54).Hasson et al examined the antibacterial activity of ethanolic extract of Saussurea lappa root against multidrug resistant (MDR) bacteria, including MRSA.The results showed bacteriostatic effects at a concentration of 2000 μg/mL and a bactericidal effect at a concentration of 6000 μg/ mL on the MRSA.Therefore, this study investigated the herb as an antibiotic because one of the reasons may be attributed to the presence of a new source of antimicrobial agents with new potential mechanisms.
Systematic screening of molecules such as antibacterial agents may lead to the discovery of new active ingredients (55).Different extracts of Senecio tenuifolius Burm plant were evaluated on MRSA and MSSA.The results showed that the methanolic extract of this plant significantly reduced the growth of these bacteria.Then, the active ingredients of this plant were purified by column chromatography.Four fractions were obtained and the fraction 3 had an inhibitory effect on the strains studied, which showed the zone of inhibition (ZOI) diameter of 15.09, 13.25, 14.12 mm, and the MIC values of 88.16, 128.11 and 116.12 μg/mL, respectively (56).These studies show the benefits of S. tenuifolius in treating skin infections.Talib et al investigated the antibacterial activity of 14 plants on various gram-positive and gramnegative bacteria.These plants displayed antibacterial effect on both bacterial groups, while their impacts were higher on gram-positive bacteria.One of the bacteria was MRSA.The results of the study showed that the MIC value was 500 μg/mL for butanol and aqueous extracts of Rosa damascene receptacles and 250 μg/mL for butanol extract of Inula viscosa flowers.The bacterium was sensitive to butanol extract of Rosa damascena receptacles (95% inhibition), I. viscose flowers (92% inhibition) and Verbascum sinaiticum flowers (70% inhibition) (57).Investigating different fractions of methanolic extract of Atractylodes japonica root showed that the fraction of CHCl3 had a good antibacterial effect on S. aureus strains.The MIC value for the fraction of CHCl3 exhibited the antibacterial effect as equal as ampicillin (32 μg/mL) against MRSA ATCC33591.Purification of this fraction gave four compounds; the compound 4 (6E, 12E)-tetradecadiene-8, 10-diyne-1, 3-diol) possessed anti-MRSA activity at a MIC value of 4-32 μg/mL.These results provide a promising basis for the potential use of this extract as well as the separation of its compounds for the treatment of bacterial infections (58).
During a research on Gynoxys verrucosa Wedd, which is one of the traditional southern Ecuadorian herbs, the results showed that the extract of this plant had a poor antibacterial activity.Purification and examination of the compounds of this plant extract showed that compound 1 (sesquiterpene lactones leucodine) had no antibacterial activity, but compound 2 (dehydroleucodine) had moderate antibacterial activity (MIC50 between 49 and 195 μg/mL).This conclusion suggests that exocyclic conjugated methylene in the lactone ring is essential for the antibacterial activity of sesquiterpene lactones.In the compound 2, in addition to the lactone ring carbonyl, there is a carbonyl in the opposite direction to the cycloheptane ring and perhaps the second hydrogen bonding site is required for this activity (59).

Family Apocynaceae
One of the folk Indian medicines used to treat skin infections is leaf and stem bark of Tabernaemontana alternifolia (Roxb).In studies, the MIC value was 600-800 μg/mL for MRSA.The aqueous extract of this plant has shown antibacterial activity against MRSA and VRSA, and it has no cytotoxic effect that confirms the validity of this plant in traditional medicine and introduces it as a candidate for the treatment of MRSA infections (47).The methanolic extract of Tabernaemontana stapfiana Britten root and stem had good antibacterial activity.The zone of inhibition diameter of this extract was 9 to 19 mm higher than other bacteria, which showed the highest inhibitory effect on S. aureus (ZOI=19 mm).The lowest MIC value was 15.6 mg/ml, which was related to S. aureus.This potent antibacterial effect of methanolic extract can be attributed to the presence of alkaloids and saponins, which are antibacterial compounds.There are also other antibacterial compounds such as flavonoids and coumarin that have synergistic effects (60).Wang et al examined the Alstonia scholaris plant and concluded that the plant had six pentacyclic terpenoids.Two compounds of oleanolic and ursolic acid have antibacterial activity limited to gram-positive bacteria.The ursolic acid had a synergistic effect along with ampicillin and tetracycline on two bacteria of S. aureus and Bacillus cereus.The ability of this compound to enhance the activity of antibiotics can be one of the most important therapeutic agents in the future (61).

Family Labiatae (Lamiaceae)
The ethanol extract of tulsi, thyme, oregano and rosemary plants belonging to Family Lamiaceae have promising broad spectrum antibacterial properties on MDR bacteria.
The ZOI is between 6 to 20 mm in tulsi, 4 to 18 mm in oregano and rosemary, and 4 to 21 mm in thyme.The presence of tannins and saponins has been confirmed in all herbs.The MIC value in the Ocimum tenuiflorum plant was ≤3.12 mg/ml for S. aureus and MRSA, which could be due to the fact that flavonoids and tannins are the main components of this plant against MRSA (40).
The two compounds of oleanolic acid and ursolic acid from Salvia officinalis (Sage) leaves showed antibacterial activity on vancomycin-resistant enterococci, Streptococcus pneumoniae and MRSA.The antimicrobial activity of ursolic acid on vancomycin-resistant enterococci suspension and S. pneumoniae and MRSA were twice as strong as oleanolic acid, which was calculated from the values obtained from MIC (62).Although the antibacterial activity of oleanolic acid and ursolic acid is not as strong as the antimicrobial drugs used in the clinic, its antibacterial activity is relatively acceptable as a plant-derived compound.Premna resinosa is one of the traditional herbs used for respiratory diseases.The findings highlighted the anti-Mycobacterium tuberculosis , anti-bacterial and antifungal activity of this plant.The fraction of dichloromethane had the highest MIC on MRSA (31.25 μg/mL) and the fraction of ethyl acetate had the highest ZOI diameter (22.3 ± 0.3 mm) on S. aureus.The effects of this plant can be related to its alkaloids, flavonoids, terpenoids, anthraquinones and phenols (49).Reports suggest an inhibitory effect of the 5-hydroxy-1,4naphthalenedione composition of the Teak leaf on Listeria monocytogenes and MRSA (63).The leaves of Rosmarinus officinalis and Tecoma capensis have a moderate antiquorum sensing activity (64).Family Labiatae can be widely used as a natural source derived from plants against MRSA (65).

Family Ranunculaceae
The goldenseal (Hydrastis canadensis L.) plant is traditionally used for skin diseases (66).LC-MS method was used to detect alkaloids and flavonoids in this extract as inhibitors of efflux pump.The extract of this plant has anti-quorum sensing activity on MRSA, which can be due to the reduction of cell signaling through the twocomponent regulatory system (TCS) of AgrCA.This extract also inhibits the production of MRSA toxin and damage to keratinocytes, in vitro .

Family Polygonaceae
Polygonum aviculare and Polygonum cuspidatum are the plants from family Polygonaceae with antibacterial activity on S. aureus (68).The ethanolic extract of Rumex nervosus has an inhibitory effect on gram-positive and gramnegative bacteria, while the hexane extract of this plant has a relatively mild antibacterial activity on gram-negative bacteria such as E. coli and Pseudomonas aeruginosa, but both extracts inhibit Candida albicans.The aqueous extract of this plant has a dose-dependent inhibitory effect on S. aureus and MRSA (69).In the essential oils extracted from Polygonum minus, GCMS showed different compounds, including aliphatic compounds such as decanal and dodecanal.The antibacterial activity of nonpolar extracts (n-hexane) showed higher antimicrobial activity on MRSA compared to polar extracts (70).

Family Solanaceae
Methanolic extract of Withania somnifera leaves from family Solanaceae on gram-positive bacteria including S. aureus and Enterococcus showed the ZOI diameters of 20.6 and 19.4 mm, respectively, at a concentration of 2 mg/mL (71).The antimicrobial activity of methanolic extracts of various organs of Bersama engleriana (family Melianthaceae) on different microorganisms including gram-positive bacteria, gram-negative bacteria, Candida and mycobacterium showed that the MICs were between 9.76 to 156.25 μg/mL.These activities were attributed to the presence of flavonoids, terpenoids, anthraquinones and phenols (36).

Family Piperaceae
The hydroalcoholic extract of Piper umbellatum (family Piperaceae) leaves has antibacterial activity and low toxicity in vitro and in vivo.Its mechanism of action is related to the change in the cell membrane and wall permeability that can be linked at least to the presence of flavonoid spresentin (39).

Family Poaceae
Dahiya showed that hexane and chloroform extracts of lemongrass were not effective on the tested bacteria (S. aureus, MRSA, E. coli, Klebsiella pneumoniae and Proteus mirabilis).S. aureus ATCC 25923 had the most sensitivity to the tested extracts (neem, tulsi, oregano, rosemary, aloevera, thyme) except for hexane and chloroform extracts of lemongrass.The highest MIC of Lemongrass extract against S. aureus was 12.5 mg/mL (42).Eleucine indica (Poaceae) is a tropical plant.It is resistant to environmental conditions and is used for many diseases, including influenza, increased blood pressure and so on.In addition to antioxidant, it showed to have anti-bacterial properties and its hexane extract exhibited significant activities against MRSA and P. aeruginosa (74).Another species of this family is Bromus inermis Leyss, which contains flavonoids.The hexane extract of this plant (MIC = 8 μg/mL) had significant effects on MRSA (75).

Family Rosaceae
The Rosa canina L. (red rose) plant contains compounds such as tellimagrandin I and rugosin B that decrease MIC values of L-lactam antibiotics against MRSA (76).The Fructus crataegi (hawthorn) also contains catechin, epicatechin gallate and epigallocatechin, which increase the effect of β-lactam antibiotics whose mechanism of action is through the suppression of genes (nor A, nor C and abc A) involved in the efflux pump (77).Rosa damascena Mill is another plant in this family, whose anti-MRSA effect has been confirmed in previous researches (36).

Family Myrtaceae
The essential oils obtained from various species of Melaleuca plant have been effective against S. aureus isolated from the ulcer of patients (78).In a study by Razmavar et al on Baeckea frutescens L. plant from this family, the findings revealed that the leaf extract of this plant has active ingredients, including flavonoids, alkaloids, steroids, terpenoids, phenols and carbohydrates.The antibacterial activity of this extract is related to these compounds (79).The ethanol extract of Rhodomyrtus tomentosa showed good antibacterial activity.Proteome analyzes revealed the effects of this plant on the expression of several major functional classes of MRSA cell proteins, including proteins responsible for biosynthesis of cell wall and cell division, surface antigens, and virulence factors.The effects of this plant on morphology and superstructure changes in treated bacteria were confirmed using transmission electron micrographs.Significant changes were observed, including changes in the cell wall, abnormal septum, cellular collapse and lysis (80).The combination of aqueous extract of Psidium guineense Swartz with β-lactam antibiotics, fluoroquinolones and carbapenems showed synergistic effects against the MRSA strains (32).

Family Rutaceae
The ethanolic extract of Clausena heptaphylla (from family Rutaceae) stem bark has alkaloids, flavonoids, saponins and steroids, but lacks tannins, anthraquinones and resins.This extract was effective on a large number of bacteria, including S. aureus.In addition to strong antioxidant properties, this plant showed better effects on gram-positive (ZOI = 6.5-9.0 mm) than gram-negative (ZOI = 3.0-4.5 mm) bacteria (45).

Family Lauraceae
Falodun et al suggested that the Persea americana plant is effective on both fungi and bacteria (81).The petroleum ether extract of the plant has an excellent antibacterial activity against MRSA with an IC50 value of 7.8 μg/mL (82).The extract of Laurus nobilis leaves has also shown a potent anti-MRSA activity (ZOI = 25 mm) and an antiquorum sensing activity (>17 mm) (46).Ethyl acetate fraction from Cinnamomum iners standardized leave has a strong antibacterial activity, especially against MRSA and E. coli with the MIC values of 100 and 200 μg/mL, respectively.Xanthorrhizol (5-(1,5-dimethyl-4-hexenyl) -2-methylphenol) was identified by different spectroscopic techniques in this plant, as the mentioned properties can be due to the presence of this compound (83).

Family Combretaceae
Ethanol extract and stem bark fractions of Terminalia fagifolia exposed good anti-MRSA activity (MIC=25-200 μg/mL and minimum bactericidal concentration (MBC) = 200-400 μg/mL).They also inhibited more than 80% biofilm formation.The images of Atomic Force Microscopy (AFM) also showed the morphological changes of the aqueous fraction of this plant on the surface of the S. aureus ATCC29213 (51).Terminalia ivorensis has traditionally been used to treat dermatological disorders, which can be due to the presence of tannins, saponins, flavonoids, coumarins and polyphenols (84).

Family Theaceae
Camellia sinensis plant from family Theaceae has antibacterial activity against MDR bacteria such as MRSA and MDR P. aeruginosa (85)(86).

Family Fagaceae
One of the members of family Fagaceae is Quercus infectoria, which is traditionally used for skin and wound infections, probably due to the presence of more than 70% tannin.It contains ellagic acid, gallic acid, syringic acid and tannic acid.This plant has shown good antibacterial activity, which leads to an increased sensitivity of MRSA to high and low osmotic pressure (87).The synergistic effect of this plant with β-lactam antibiotics has been shown to interfere with staphylococcal enzymes such as autolysins and β-lactamase (88).This plant also had antibiofilm effects through its effect on the bacterial cell wall (89).

Family Fabaceae
The antibacterial compounds were obtained from the polar fractions of Ononis hirta (a.p) and Ononis sicula (a.p).The antibacterial activity was well observed on many bacteria, including S. aureus and Bacillus cereus, which are causes of food poisoning.These plants contain flavonoids and terpenoids (36).Two new flavonoids, called bakuisoflavone and bakuflavanone, were identified in the Psoralea corylifolia fruit; these compounds exhibited significant anti-MRSA effects (90).In the genus Abrus from this family, amorphaquinone and pendulone compounds have been shown to be effective not only against Leishmania donovani and Plasmodium falciparum, but also on S. aureus and MRSA (35).
A large number of studies have been carried out on the identification of the antimicrobial effects of plant compounds on different microbial agents (97), which have also yielded favorable results.Wild plants have bioactive ingredients with potential activity against diseases associated with microorganisms (98).Zhang et al examined 58 traditional herbs and argued that their findings were consistent with the traditional use of these herbs.By detecting and isolating the potential substances of these plants, they can be used to discover a new antimicrobial agent for treatments (50).

Clinical trials
In addition to in vitro use of plants, researchers have investigated the in vivo effects of these plants on different bacteria, including MRSA; remarkable effects of these plants have been reported on inhibiting this bacterium (91,98).Yamada et al examined the inhaled effect of catechin tea on aged patients with cerebrovascular ailments whose sputum contained MRSA.These patients were exposed to the herb inhaled three times a day for three weeks.The results showed that the reduction in MRSA count in the sputum was 47% in the treatment group and 15% in the control group and this difference was significant.Although the inhalation of this plant has reduced the count of this bacterium, its use to control the MRSA-associated infections is controversial (99).Buenz et al stated that the Atun tree (Atuna racemosa) is one of the plants identified in the 400-year book of plant history to heal the MRSA-related infections.They showed that the Atun tree extract at the doses of 10 times greater than MIC value are effective against MRSA for topical use in humans (100).Tea tree oil is one of the ingredients traditionally used to treat skin diseases, as researchers have confirmed the effects of these compounds.The body washing with these compounds can prevent colonization of microorganisms on the body (101)(102)(103).

Conclusion
The emergence of expanding antibiotic-resistance genes in the bacterial population has led to the identification of new antimicrobial drugs.The most promising of these compounds are drugs affecting microorganisms through various mechanisms to eliminate microorganisms with subsequent drug actions in case of resistance to a mechanism, hereby contributing to treat MDR bacterial infections.Consequently, there is a need for concentration to detect the active components of these compounds, as well as to pursue simultaneously the development of this product as a natural product.The results of this study showed that different plants belonging to various families have the ability to inhibit S. aureus and MRSA and can be used to achieve effective drugs against these bacteria.Considering the synergistic effects of some of these plants with antibiotics used in the clinic, it is suggested to be evaluated the combined effects of different parts of the plants in combination with antibiotics in future studies.

Table 1 .
The list of medicinal plants and their antibacterial activities