Antibacterial and antifungal potentials of the solvents extracts from Eryngium caeruleum, Notholirion thomsonianum and Allium consanguineum

Herbal therapies have long history for their use in various ailments. Being comparatively harmless, the natural products have attracted the focus of innovative researchers in the treatment of various challenging diseases [1, 2]. Microbial infections including tuberculosis, urinary tract infections (UTI’s), meningitis, dermatitis, otitis media caused by bacterial and fungal strains are among the challenging diseases for the scientific community [3‐5]. The morbidity rate of diseases originated from bacteria and fungi is surpassing various other diseases [6, 7]. The use of antibacterial and antifungal drugs is a main approach among the therapeutic options to treat bacterial and fungal infections [8]. But still there are numerous factors which minimize the therapeutic outcome of the antibiotic therapy. Beside various factors, the microbial resistance has prominently diminished the efficacy of antibiotics and the microbial resistance is the major cause of failure to treat bacterial and fungal infections [9, 10]. Moreover, adverse drug reactions and hypersensitivity reactions associated with the use of various synthetic antimicrobial agents have decreased the interest of scientists to synthesize novel drugs having antimicrobial potentials. Therefore, the attention of researchers is mainly focused towards the natural compounds isolated from various plants [11‐16]. Plants have been reported to possess antimicrobial potentials due to the presence of various secondary metabolites [17, 18]. The alkaloids and flavonoids have been reported to possess strong antimicrobial potentials against bacteria and fungi [19, 20]. Flavonoids like robinetin, myricetin, apigenin, rutin, Kuwanon C, mulberrofuran G, albanol B, kenusanone A and sophoraflavanone G isolated from various plants like Morus alba L., Morus mongolica Schneider, Broussnetia papyrifera (L.) Vent, Sophora flavescens Ait and Echinosophora koreensis Nakai have been reported to possess strong antibacterial potentials [19]. Similarly, alkaloids like sampangine and azafluorenone isolated from Cananga odorata and Mitrephora diversifolia respectively have also been reported to possess strong antifungal activities [21‐24]. Varieties of plants belonging to different families have been scientifically verified for antimicrobial potentials. The scientific verification of a specific plant for the specific pharmacological activity is based on the traditional knowledge of species from the plant family. A specific biological potential of specific plant can be heralded by the ethnobotany and ethnomedicine [25].

Eryngium caeruleum belongs to the family Apiaceae. Several species of this genus have been reported to possess antimicrobial activities [26]. Similarly, Notholirion thomsonianum belongs to the family Liliaceae. This plant has been used ethnomedicinally for the treatment of various infectious diseases especially intestinal [27]. Likewise, Allium consanguineum belongs to the family Amaryllidaceae. A wide variety of species of Allium genus have been reported to possess notable antimicrobial properties in which the onion and garlic are the prominent candidates [28‐30]. The selection of these plants species for antimicrobial studies was made on the basis of their traditional uses as well as their genera and family background. Similarly, the rhizomes of N. thomsonianum and A. consanguineum were exploited for extraction due to ethnomedicinal use of rhizome. Secondly, the rhizomes and underground part of multiple plants of the families of these plants have been reported to be rich sources of numerous bioactive compounds i.e., Allium sativum and Allium cepa [31]. Likewise, the aerial parts of several species of Eryngium are reportedly good source of secondary metabolites and possess pharmacological potentials [32]. Therefore, the aerial parts of E. caeruleum were employed for extraction. Therefore, the current study was aimed to evaluate the antibacterial and antifungal potentials of Eryngium caeruleum, Notholirion thomsonianum and Allium consanguineum and scientifically validate its folkloric uses.

Microbes are considered as the mainstay and origin of multiple diseases. Microbial infiltration into the body tissues and blood lead to various diseases some of which are difficult to treat and extremely lethal [49, 50]. The etiology of various humans’ infections may be related to bacteria, virus, fungi and protozoa. The bacterial infections like upper respiratory tract infection, lower respiratory tract infection, tuberculosis, pneumonia, bacillary dysentery etc. are getting more and more attention due to the increasing morbidity and mortality due to these infections [51, 52]. Similarly, most of the fungi have the ability to cause infection without getting entered into the blood stream or mucosa. Such type of fungal infections involve disruption of dermal layer and are contagious [53]. Moreover, the fungi may cause a lot of systemic infections as well [54]. To avoid various health complications, a wide variety of antimicrobial drugs are used which avoid and alleviates the symptoms caused by microbes. The antimicrobial agents may interrupt the synthesis of metabolites which are necessary for the basic integrity of microbes including bacteria and fungi [55, 56]. However, the main problem with the use of antimicrobial and other drugs is the hazardous and toxic effects associated with their use [57, 58]. Secondly, many microbes develop resistance to a specific group of drugs and they become less susceptible to that specific drug [55]. Fortunately, nature is kind enough to provide remedy for almost every disease [59]. The natural bioactive compounds being biodegradable and hydrolytic have been reported to possess comparatively low toxicity and high efficacy [60]. Investigators are in continuous search for the exploration of novel sources of more effective compounds for the treatment of challenging infectious diseases [61‐63]. As previously reported, plants possess antibacterial secondary metabolites which are getting more and more importance due to their negligible toxicity and adverse effects [64, 65]. The aim of the current study is to have a step towards the achievement of novel natural antimicrobial agents. Results of the current study revealed that N. thomsonianum possess strong antibacterial and antifungal results. The MIC values of positive control and chloroform fraction were going considerably parallel i.e., if we cursorily observe the Table 2, we can figure out the antibacterial potential in terms of MIC (39.67, 280.00, 47.33, 73.33, 63.33 μg/ml) of chloroform fraction and that of positive control (2.03, 3.867, 2.367, 1.67, 0.503, 1.67 μg/ml), which are relatively comparable. The MICs of chloroform fraction has been figured out to be smaller than 100 μg/ml against majority of the test strains, which reveals the significance of this fraction. This significance is in the terms of therapeutic applications against various bacterial infections. As variety of antimicrobial natural compounds and antibiotics have their MIC values lower than 100 μg/ml, which are effective against various bacterial infections and are considered as therapeutically as well as statistically important data [66, 67]. Similarly, the antifungal activity of chloroform fraction is also dominant. It was also observed that the chloroform fraction was the most active one against bacterial and fungal strains. Against A. niger and A. flavus the chloroform fraction demonstrated MFC values of 63.00 ± 4.93 and 29.33 ± 5.48 μg/ml respectively, which are less than 100 μg/ml, which can be considered to be significant in the context of therapy of various diseases [68]. The results obtained in the current study can be correlated with the previous publications. Other species of Allium also possess effective potential against microbes i.e., Allium sativum L. (garlic), Allium ampeloprasum L. (elephant garlic) and Allium cepa have been reported to possess strong antibacterial and antifungal activities [69]. Important antibacterial compound i.e., allicin has also been isolated from Allium sativum which has been reported to be active against various pathogenic bacterial strains [70]. In the same way, numerous species of Eryngium have been reported to possess antimicrobial potential. Eryngium palmatum one of medicinally important specie of Eryngium has been verified to be active against microbes [71]. Similarly, the Eryngium genus has also been reported to inhibit the methicillin‐resistant Staphylococcus aureus strains significantly [72]. The results of the previous reports goes parallel with the results of our current investigational study which indicate that like other species of Allium and Eryngium the E. caeruleum, A. consanguineum and N. thomsonianum are also prominent candidates of these genera. The study reveals that among the three plants, N. thomsonianum was rich in antimicrobial agents and secondly it may also be implied that the chloroform fraction was rich in such secondary metabolites which confer antimicrobial potential to this plant.

Based on our current investigations it can be concluded that N. thomsonianum, A. consanguineum and E. caeruleum possess considerably sufficient antibacterial and antifungal potentials. It may also be concluded that antimicrobial potential of various samples of these plants might be due to wide variety of compounds present in these plants. Moreover, we observed that specifically the chloroform and upto some extent the ethyl acetate fractions of these plant contain considerably high activity. These two fractions (in each plant) are potent targets to be subjected to bio-guided isolation and exploration of novel natural antimicrobials.