The presence or absence of different phytochemicals in plant extract plays a major role in antioxidant and antibacterial activities of a specific plant part . In the present study, qualitative phytochemical screening of E. ramosissimum revealed the presence of significant amount of secondary metabolites like phenolics, flavonoids, steroids, and tannins (Table 1). Previous studies also confirmed the presence of various phytochemicals in different parts of E. ramosissimum as reported in the present work [10, 11]. To support our study, Chiu et al.  also identified sterol compounds from aerial parts of E. ramosissimum with chloroform–methanolic extract.
The phytochemical analysis of E. ramosissimum stem extract using GC–MS showed the presence of 24 compounds with palmitic acid (44.3, 34.4, and 19.4% in methanolic, ethyl acetate, and petroleum ether extracts, respectively) and linoleic acid (41.4% in petroleum ether extract) as major constituents (Table 2). Palmitic acid is a saturated fatty acid (16-C long chain molecule), an essential component for human body and could be supplemented in diet or made endogenously from the other fatty acids, amino acids, and carbohydrates . It has a major pathological role in metabolic syndromes, cancer, inflammation, cardiovascular, and neurodegenerative diseases and major proportion of saturated fatty acids found in human body cells and serum are comprising of this palmitic acid .
As reported in our study, Alebous et al.  also revealed the presence of linoleic acid (4.6%) in essential oil extracted from aerial parts of E. ramosissimum. Linoleic acid is one of the important polyunsaturated fatty acids which is necessary energy per day (at least 1–2%) for normal human growth and development process and considered as a precursor in the synthesis of arachidonic acid and eicosanoids . The compound is most commonly found in the seeds, nuts, oils, and cereals of various plants and major vegetable oils like corn, olive, cotton seed, palm, sunflower, and coconut comprising about 1% of linoleic acid . Linoleic acid is also involved in various health promoting properties like reducing the catabolic effects of immune stimulation, facilitates growth regulation and promotion, reduces body fat, anticarcinogenic and antiatherogenic activities .
Among the 24 compounds recorded in our study, only palmitic acid, hexacosane, and octacosane are noticed in all the tested extracts (Table 2 and Fig. 1). The compounds like, n-tridecane, methyl palmitate, neophytadiene, 3,7,11,15-tetramethyl-2-hexadecen-1-ol, ethyl palmitate, methyl linoleate, linoleic acid, n-eicosane, methyl 9,12,15-octadecatrienoate, sulphurous acid, cyclohexylmethyl hexyl ester, cyclopentane carboxylic acid, bis(2-ethylhexyl) phthalate, 4-methylpentyl ester, campesterol, squalene, and solanesol were recorded as least represented phytochemicals in any one of the solvent extract.
Flavonoids are one of the major types of polyphenols and most of them have been reported to have antioxidant, anti-inflammatory, and antidiabetic activities . The amount of TPC observed in the present study was noticeably higher than the earlier reports. Previously, methanolic extract of the stem of Equisetum telmateia (E. telmateia) was recorded with 262.7 ± 1.0 mg RU/g pf TPC . Stajner et al.  reported 1.75 ± 0.09 mg/g of TFC in aerial parts of E. ramosissimum phosphate buffer extract. The results of this study revealed that the extracts of high polar solvents like methanol and aqueous showed highest amount of TPC and TFC in E. ramosissimum stem which showed highest extraction efficiency (Fig. 2). The polarity of solvent has a significant role in quantity of TPC and the efficiency of extraction for TPC and TFC is reduced with the decrease in polarity of solvents. It was well known that hydrophilic and hydrophobic features of phytochemicals recorded a high influence on their solubility, and hence, polarity of solvents used has a potential role in extracting efficiency of these phytocompounds .
Antioxidants can diminish the adverse effects of free radicals, viz., reactive oxygen species (ROS) and reactive nitrogen species (RNS) that are generated during cellular metabolism. The ROS exert supportive effects on cellular redox signalling and immune functioning even at low concentrations. At higher concentrations, ROS and RNS deregulate several cellular functions and often lead to diverse pathological illnesses . The use of plant-based natural antioxidants like flavonoids, phenolics, and tocopherols are biologically act at molecular level and reported to inhibit/reduce the formation of free radicals . Antioxidant capacity of plant extracts could be due to the existence of polyphenolic compounds which have the ability to donate hydrogen atoms to their hydroxyl groups .
The DPPH was used as a source of free radicals, since it simulates ROS and RNS by in vitro that affect biological systems and involved in inhibiting the oxidative stress-induced cellular damage and lipid peroxidation . To support our study, significant free radical scavenging effect with the DPPH method was reported by Paulsamy et al.  in methanolic extracts of E. ramosissimum whole plant with an IC50 of 78.58 µg/mL. According to Li et al. , ethyl acetate extract of E. ramosissimum at 200 µg/mL showed comparable DPPH activity with an IC50 of 43.41 ± 7.68 µg/mL. Previously, Stajner et al.  reported comparable antioxidant effect of aerial parts of E. ramosissimum, Equisetum arvense (E. arvense), and E. telmateia with phosphate buffer extracts using FRAP methods with an effective IC50 of 5.44 ± 0.72, 2.85 ± 0.45, and 44.1 ± 2.11 µg/mL, respectively.
Methanolic extract of whole plant parts of E. ramosissimum showed ABTS scavenging activity of 1946.36 ± 2.12 µm of TE/g DW  as like our study. Also, ethanolic extract of E. arvense exhibited higher scavenging activity in ABTS assay with an IC50 of 98.13 ± 3.84 . Our results of O2− radical scavenging activities are in accordance with studies of Nagai et al.  who reported significant O2− radical scavenging activities of aqueous and ethanolic extracts of E. arvense aerial parts with 7.33 and 54.2% of inhibition, respectively. They also reported 12.8 and 80.6% of inhibition by the stem of E. arvense with aqueous and ethanol extracts. Likewise, Canadanovic-Brunet et al.  reported the OH− radical scavenging effect of the ethyl acetate and aqueous extracts of E. arvense aerial parts with the EC50 of 2.29 ± 0.11 and 3.29 ± 0.16 mg mL−1, respectively. The values for antioxidant activity of methanolic and aqueous extracts of E. ramosissimum stem exhibited no significant changes in ABTS, hydroxyl radical, superoxide, and FRAP assays (Fig. 3).
The stem extracts of E. ramosissimum were effective against the growth of pathogenic bacteria (done by microdilution method) like S. epidermidis, B. subtilis, R. equi, MRSA, E. coli, V. cholerae, S. typhi, P. aeruginosa, K. oxytoca, and C. freundii which are recognized as well-known causative agents of UTIs (Table 3 and supplementary file). Sarkar et al.  reported a high degree of antibacterial activity in ethyl acetate extract of E. ramosissimum whole plant against E. coli and S. aureus with the zone of inhibition of 7–8 mm. Ethyl acetate extracts of the aerial parts of Equisetum hyemale showed good range of antibacterial activity (13.1–52.4 mg/mL) against the bacterial strains S. aureus, E. coli, and P. aeruginosa .