Phytochemical constituents of fucoidan (Padina tetrastromatica) and its assisted AgNPs for enhanced antibacterial activity

Abstract

Biological synthesis of nanomaterials is a growing innovative approach and it was broadly utilised in the field of nanotechnology and nanomedicine. This study illustrates that biosynthesis of silver nanoparticles (AgNPs) using fucoidan extracted from seaweed Padina tetrastromatica. The functional groups of extracted fucoidan were characterised by Fourier transform infrared spectroscopy (FTIR) and used to NPs synthesis. Synthesised AgNPs were characterised by ultraviolet–visible spectra, scanning electron microscope, energy dispersive X‐ray, transmission electron microscope, selected area electron diffraction and FTIR. In this study, their main focus is enhancement antibacterial activity of AgNPs coated antibiotics against antibiotic resistant bacteria. Among the microorganisms, Serratia nematodiphila was resistant to novobiocin and penicillin, but it was sensitive to AgNPs impregnated antibiotic discs. The zone of inhibition was 12 and 15 mm. The synergistic effect of combined antibiotics and AgNPs resulted in increased fold area which was greater than the sum of their separate effects. It reveals that AgNPs are highly sought in the medicinal field due to their broad spectrum of antibacterial activity and relatively cheaper. This enhanced synergistic effect potentially superior to control the growth of bacteria and it is the budding process for the development of new remedial agents for severe diseases.

1 Introduction

Fucoidan is the one of a major medicinal source having application in clinical, haematological and biochemical medicines. Exploring about fucoidans degrading enzymes fucoidanase's are the main caption in biological chemistry division nowadays. Fucoidan is the major source of most of the marine brown seaweeds [1]. Green fabrication of nanomaterials using green compounds is an eco‐friendly process and easy to handle. There are many green compounds that are used for the synthesis of silver (AgNPs) and gold NPs (AuNPs) such as sugar beet pulp, sorghum bran, tryptophan (amino acid) wool keratin, sucrose ester micellar, maltose and sucrose (disaccharides), starch polysaccharide, honey, glucose, fructose and sucrose sugar mixtures, natural hydrocolloid gum kondagogu [2, 3, 4, 5, 6, 7, 8, 9, 10, 11].

Chemotherapy is very good tool for the management of diseases control since the 19th century. There is a countless of the diseases are affect the human beings spread through many ways such as airborne, waterborne and food borne. Antibiotics are the major chemical compounds playing an important role in medicine to cure thousands of infections caused by bacterium and fungi. The discovery of new metal‐based drugs has been largely based on the ability of metals to increase the inhibitory potential of chemotherapy agents. Efficacy of some therapeutic agents has been reported to have increased on coordination to transition metals [12]. AgNPs are the major advanced materials growing vigorously to control the bacterium present in the human infectious samples, animal infections, plant diseases etc.

Use of nanotechnology in immunology, design and delivery of antimicrobial drugs and diagnosis and control of cross‐infections, in particular in overcoming antibiotics‐resistant pathogens have been explored as a promising alternative to the current antibiotics‐based approaches [13]. The field nanotechnology was focused on various challenges in controlling infectious diseases, encompassing diagnosis of bacterial resistance, delivery of antimicrobial agents and vaccination using nanomaterials [14]. The various biogenic materials are used for the synthesis of AgNPs such as plants [15, 16, 17, 18, 19, 20, 21], bacteria [22, 23], fungi [24, 25], yeast [26] and marine algae [27, 28]. The biosynthesised AgNPs are playing an excellent role in antimicrobial activity against various pathogenic microbes such as plant pathogens [15], clinical pathogens [29], drug resistance nosocomial gram‐negative bacteria pathogens [30], foodborne pathogens [19], waterborne pathogens [31], fish bacterial pathogens [16], multi‐drug resistant bacteria [17], phytopathogenic fungi [26] and various types of gram‐positive and gram‐negative bacterial isolates [32, 33, 34, 35, 36, 37, 38].

Antibiotic resistance by pathogenic bacteria and fungi has been continuously increasing over the past decade due to the long‐time treatment and exposure. Owing to the resistance to antimicrobial agents are the major implications to cause morbidity, mortality and healthcare cost [39]. Hence, there is a need for the development of new therapeutic agents. AgNPs act as a good antibacterial agent which was combined with antibiotics; it enhances the action of antibiotics against severe pathogenic bacteria and fungi. It was achieved by the colloidal AgNPs coated antibiotics discs [40].

In this paper, the fucoidan was used to synthesise the AgNPs extracted from P. tetrastromatica seaweed. When compared with raw marine algae, the fucoidan is novel biomedical sulphated polysaccharide compound newly used to synthesise purified AgNPs. Morphological and crystalline characterisation was performed. The main aim is to assess the enhanced antibacterial activity of AgNPs combination with different antibiotic discs against pathogenic bacteria by disc diffusion method.

2 Materials and methods

2.1 Chemicals

All the chemicals, media and commercial standard antibiotic discs were purchased from Hi‐Media laboratories, Mumbai, India.

2.2 Extraction of fucoidan

The fucoidan is extracted as described by Mian and Percival [41] and adapted from Souchet [42]. Sulphated polysaccharide fucoidan was extracted from the milled seaweeds (30 g) using selective solvents with a constant mechanical stirring at 40 rpm. First, ethanol 85% (v/v) was used to extract pigments and proteins. The solvent was separated from residual seaweeds by vacuum filtration using Whatman No. 1 filters. Residual seaweeds were treated with calcium chloride (CaCl₂) 2% (w/v) at 70°C in order to precipitate fucoidan from the mixture, and then centrifuge the solution for fine separation of fucoidan. Fucoidan was extracted from the residual seaweeds with HCl (0.01 mol/l, pH 2) at 70°C (3 h), and then centrifuged. The sulphated polysaccharide was dialysed (cut‐off 1000 Da) for 48 h and the fucoidan solution was freeze‐dried and kept at 4°C until use. The fucoidan was used for characterisation by using compound analysis by Fourier transform infrared spectroscopy (FTIR).

2.3 Phytochemical screening of various extracts of fucoidan

Qualitative estimation of total polysaccharide was done by phenol–sulphuric acid method [43]; protein content was analysed by using folin phenol reagent [44] and sulphate content was determined by using turbidimetric method [45]. The presence of fucose in the extract was analysed by the method of Dubois et al. [43]. Alkaloids, flavonoids and saponins were estimated by following the method of Harborne [46]. The presence of xylose was estimated by orcinol–sulphuric acid method [45]. Galactose content was estimated by phenol–sulphuric acid method using galactose as standard [43]. The presence of phenol and tannins were determined according to the method described by Edeoga et al. [47]. Uronic content was analysed by carbazole–sulphuric acid method [48].

2.4 Green synthesis of AgNPs by using fucoidan

AgNPs were synthesised by using the fucoidans of P. tetrastromatica (Pt Fucoidan). About 10 ml of Pt fucoidan was added to 90 ml of 1 mM silver nitrate (AgNO₃) for the synthesis of AgNPs and the flask was kept in magnetic stirrer for constant stirring. Colour change of the medium was noted by visual inspection confirming the green synthesis of AgNPs.

2.5 Characterisation of fucoidan‐assisted synthesised AgNPs

The reduction of Ag ions to NPs was primarily identified by double beam ultraviolet–visible (UV–vis) spectrophotometer (Perkin Elmer, Singapore) at different wavelength regions from 350 to 650 nm. The shape and size of the AgNPs were characterised by using scanning electron microscope (SEM) (Hitachi, Model: S‐3400N) and transmission electron microscope (TEM) with selected area electron diffraction (SAED) (PHILIPS, CM200). X‐ray diffraction (XRD) assay (Bruker, Germany, model D8 Advance) was performed for the confirmation of crystalline structure of synthesised NPs. The presence of elemental Ag was confirmed by energy dispersive X‐ray (EDX). The FTIR analysis was carried out in a Make – Bruker Optik GmbH Model No – TENSOR 27. The synthesised NPs were grinded with KBr pellets and analysed at wave number from 4000 to 400 cm⁻¹.

2.6 Enhanced antibacterial activity of AgNPs

The enhanced antibacterial activities of fucoidan‐mediated synthesised AgNPs were evaluated by disc diffusion method. Synthesised AgNPs were impregnated with antibiotic discs such as ampicillin, tetracycline, novobiocin, penicillin, kanamycin, gentamycin, chloramphenicol, streptomycin and ciproflaxin and determine the enhanced antimicrobial activity against clinical isolates of Bacillus subtilis, Bacillus sp., Serratia nematodiphila, Klebsiella planticola, Klebsiella Pneumoniae and Streptococcus sp. Clinical pathogens were cultivated in Luria‐Bertani broth at 37°C for 24 h incubation and used as inoculums. The commercial standard antibiotic disc was impregnated with 25 µl of 100 nM concentration of the freshly generated AgNPs to study the synergistic effect against clinical pathogens. The 24 h bacterial cultures were swabbed on the plates containing Mueller‐Hinton Agar and placed the AgNPs impregnated antibiotic discs. The inoculated plates were incubated at room temperature for 24 h and measure the zone of inhibition around the disc. The enhanced fold area was assessed by calculating the mean surface area of zone formation engendered by an antibiotic alone ‘a’ and AgNPs impregnated antibiotics ‘b’. Hence, the increased fold area was calculated by the formula (b ² −a ²)/a ² [49].

3 Results and discussion

3.1 Extraction of fucoidan

Sulphated polysaccharide fucoidan was mostly present in the brown seaweeds especially Padina tetrastromatica [50, 51]. The depigmented algal powder (DAP) from P. tetrastromatica contains fucose as one of the constituent sugar, which was extracted with water and polysaccharides were isolated there from by repeated precipitation with ethanol. This water extracted fraction (named as PtWE (padina tetrastromatica water extract)) amounted to 8% of DAP dry weight and contained fucose as the major neutral sugar. Such as the sulphated fucans of other brown seaweeds, the polysaccharides from P. tetrastromatica also contained galactose and xylose, but it did not contain any amino sugar. The uronic content of PtWE was 14%, possibly due to the presence of alginic acid. Sodium alginates are soluble in water, but they form insoluble precipitates with calcium (Ca) salts. Therefore, these macromolecules were removed from the water extract by precipitation with CaCl₂. Indeed, fractionation of PtWE with CaCl₂ yielded three populations: a fucoidan‐containing fraction soluble in CaCl₂ (PtWE‐I) and two other fractions (PtWE‐II and PtWE‐III) derived from the CaCl₂ insoluble material.

3.2 Phytochemical screening

The preliminary phytochemical analysis showed the presence of phytoconstituents such as alkaloids, phenols, polysaccharide, sulphate, xylose, uronic acid, flavonoids and proteins. The algal powder was subjected to fractionation by various solvents for investigation of various phytocomponents. Table 1 shows the phytochemical constituents of various extracts of the algal powder sample.

Table 1.

Phytochemical screening of various extracts of P. tetrastromatica

Components	DAP	Fucoidan	PtWE‐I	PtWE‐II	PtWE‐III
fucose	+	+	+	+	+
galactose	+	+	+	−	−
xylose	+	+	+	−	+
uronic acids	+	+	+	+	+
polysaccharides	+	+	+	−	+
alkaloids	+	+	+	+	+
saponins	−	+	−	−	−
phenol	+	+	+	+	+
tannins	+	−	+	−	−
protein	−	+	+	+	+
flavonoids	+	+	+	−	+
sulphate	+	+	+	+	−

+ presence, − absence.

3.3 FTIR of extracted fucoidan

The FTIR spectrum of Pt fucoidan is shown in Fig. 1. A broad and strong band was formed in both the extracted fucoidan and commercially available fucoidan (which is derived from Fucus vesiculosus) at 3209 and 3347 cm⁻¹ due to the presence of O–H stretching polyphenolic alcohols and N–H stretching of amines, 1825 cm⁻¹ corresponds to the C = O stretching of carboxylic acid derived anhydrides, the absorption band at 1560 cm⁻¹ was occurred for the N–H stretching of amines and 1363 cm⁻¹ due to the presence of –NO₂ aliphatic nitro groups, the narrow peak at 1230 and 1225 cm⁻¹ indicates C–N stretching of aliphatic amines and S and O stretching vibration of the sulphate group, a small band at 1051 cm⁻¹ was assigned for the C–O (cm⁻¹) stretching of carboxylic and alcohol groups, a weak band at 781 and 778 cm⁻¹ (C–O–S, secondary axial sulphate) was occurred due to the S–O sulphonates groups in the fucoidan indicated that the sulphate group is located at position four of the fucopyranosyl residue [52, 53].

Fig. 1.

FTIR spectra of standard fucoidans and P. tetrastromatica fucoidan (Pt fucoidan)

3.4 Green synthesis of AgNPs by using fucoidans

3.4.1 Visual inspection

Fig. 2 shows the visual observation of synthesis of AgNPs by using extracted Pt fucoidan solution. Figs. 2 a and b exhibit the synthesis of AgNPs after 24 h incubation of Pt fucoidan with AgNO₃ solution. It can be observed that the colour change from yellow to dark brown was formed immediately after addition of Pt fucoidan to the AgNO₃ solution indicates synthesis process of NPs was started. After 24 h, the occurrence of stable dark brown colour indicates the completion of reduction of Ag ions to AgNPs. The formation of dark brown colour was raised due to the excitation of surface plasmon vibrations in the surface of AgNPs. The same colour changes were observed in plant synthesised AgNPs by using Lippia citriodora leaves extracts, Nelumbo nucifera leaf extract and black pepper seed extract [54, 55, 56].

Fig. 2.

Fucoidan extract of P. tetrastromatica treated with AgNO₃

(a) At the beginning of the reaction, (b) After 24 h of reaction shows brown colour indicates formation of AgNPs

3.4.2 UV–vis spectroscopy

The UV–vis spectra recorded from the Pt fucoidan reaction vessel at different time intervals were shown in Fig. 3. The strong surface plasmon resonance band was centred at 440 nm which is characteristic peaks of AgNPs. The spectrum clearly shows that the absorbance of AgNPs was increased with increased incubation time, which clearly indicates the formation of increased number of AgNPs in the reaction mixture [57]. Thus synthesised AgNPs were stabled for even a month due to the process of stabilisation between extract and NPs. This indicates the presence of capping molecules in the extract which bind on the surface of the NPs. After a month, the aggregation of AgNPs was identified by the occurrence of precipitation in the reaction mixture due to the lack of stabilisation. The AgNPs synthesised from plant extracts by Jha et al. [18] and Lin et al. [19] was matched with our present report. The report was compared with P. tetrastromatica leaves mediated AgNPs synthesis its rapid synthesis and we got stable AgNPs [27].

Fig. 3.

UV–vis spectra of AgNPs synthesised by Pt fucoidan, strong broad band was showed at 450 nm

3.4.3 Transmission electron microscopy

A representative TEM image recorded from the AgNPs synthesised from fucoidan film deposited on a carbon‐coated copper TEM grid is shown in Fig. 4. This image shows individual Ag particles as well as some aggregates. The morphology of the NPs is highly variable, with spherical and occasionally triangular NPs observed in the micrograph. Under surveillance of such images in a microscope, these congregations were found to be aggregates of AgNPs with the size range 4–25 nm with the average diameter range of 17 nm. The NPs were not in direct contact even within the aggregates, indicating stabilisation of the NPs by a capping agent fucoidan. AgNPs were synthesised by the reaction of Ag+ ions with Pt fucoidan, and the stability is likely to be due to capping with carbohydrate molecules in the fucoidan [56]. The separation between the AgNPs seen in the TEM image could be due to capping by sugar molecules and would explain the UV–vis spectroscopy measurements, which is characteristic of well‐dispersed AgNPs. The Ag particles are crystalline, as can be seen from the selected area diffraction pattern recorded from one of the NPs in the aggregates. It shows four concentrated diffraction rings indexed for the planes are (111), (200), (220) and (311) for crystalline Ag [7].

Fig. 4.

TEM micrograph of AgNPs synthesised using Pt fucoidan

(a) 50 nm scale bar, (b) SAED pattern

3.4.4 SEM and EDX analyses

SEM image shows the morphological characters of resulted Pt fucoidans mediated synthesised AgNPs (Fig. 5). Pt fucoidan – AgNPs shows many of undefined and rectangle shaped NPs. The clear structure was not found in the SEM image because the biomolecules responsible for the NPs synthesis were found on the surface of the NPs [20]. The same shaped NPs were observed from Ag, Au and bimetallic NPs synthesised from filamentous fungus Neurospora crassa [24]. The irregular shapes of NPs were found due to the agglomeration of NPs in the fucoidan medium [3]. Analysis through EDX confirmed the presence of elemental Ag [21]. Strong signal at 3 keV confirms the presence of AgNPs formation in the solution (Fig. 6). The weak signals were observed for oxygen, nitrogen and carbon due to the biochemical molecules of fucoidans responsible for the AgNPs synthesis. A similar report was already proved in Catharanthus roseus, sorghum bran extract and wool keratin [3, 5, 28, 58]. Apart from that we got a very good strong signal when compared with P. tetrastromatica leaved mediated AgNPs [27].

Fig. 5.

SEM images of AgNPs synthesised using Pt fucoidan extract

(a) Magnification 1000 nm, (b) 500 nm

Fig. 6.

EDX spectrum of AgNPs prepared using Pt fucoidan extract

3.4.5 XRD assay

XRD pattern of fucoidan synthesised AgNPs (Fig. 7) shows four intense peaks in the spectrum values ranging from 10° to 90°. XRD spectra of pure crystalline Ag structures have been published by the Joint Committee on Powder Diffraction Standards (file no. 04‐0783). A comparison of our XRD spectrum with the standard confirmed that the Ag particles formed in our experiments were in the form of metallic crystalline phases coexist. The crystalline peaks for Pt fucoidan formed at 2θ values of 38°, 44°, 64° and 77 ° can be indexed as (1 1 1), (2 0 0), (2 2 0) and (3 1 1), respectively, planes for face centred, cubic (fcc) Ag. The other peaks at 2θ  = 33° are thought to be related to crystalline and amorphous organic phases accompanying crystallised AgNPs, as stated in the discussion of the TEM images. These unidentified crystalline peaks (*) are also apparent in many works [55, 59, 60, 61]. This predicts that the synthesised NPs by using the Pt fucoidan are pure and crystalline in nature.

Fig. 7.

XRD pattern of AgNPs synthesised by using Pt fucoidan shows crystalline structure

3.4.6 Fourier transform infrared spectroscopy

Fucoidans are sulphated polysaccharides having the lot of sugar residues such as fucopyranocyl residues, fucose and xylose and minor amount of glucose and mannose were present [51]. The biomacromolecules in the fucoidans might be responsible for the synthesis of AgNPs (Fig. 8). Pt fucoidan synthesised AgNPs having the weak bands are 2982, 2653 and 2334 cm‐1 indicated the presence of O–H stretching carboxylic acid group. At the absorption bands of 1567 cm⁻¹ was observed due to the N–H bending of amines, the low absorption band at 551 cm⁻¹ corresponds to the presence of alkyl halides. The saccharides such as starch (polysaccharide), sucrose and maltose (disaccharide) are used for the synthesis of AgNPs on the green route [7, 8].

Fig. 8.

FTIR spectrum of silver nanoparticles (SNPs) synthesised from Pt fucoidan

3.4.7 Calculation of concentration of the AgNPs

The concentration of AgNPs was determined by the method which has been previously reported for Liu et al. [62] and Kalishwaralal et al. [63] for AuNPs and AgNPs, respectively. The calculation is as follows.

Determine the average number of atoms per NP [62, 63]

$$N=\frac{\pi \rho D^3}{6M}{N}_{\mathrm{A}}$$

where N is the number of atoms per NPs, π  = 3.14, ρ is the density of fcc Ag (10.5 g cm⁻³), D is the average diameter of NPs (17 nm = 17 × 10⁻⁷ cm), M is the atomic mass of Ag = 107.868 g (silver only not Ag salt), N _A is the number of atoms per mole (Avogadro's number = 6.023 × 10²³)

$$\mathrm{i}.\mathrm{e}.N=97561523.7$$

Determine the molar concentration of the NP solution [62, 63]

$$C=\frac{N_{\mathrm{T}}}{\mathrm{NV}{\mathrm{N}}_{\mathrm{A}}}$$

where C is the molar concentration of NP solution, N _T is the total number of Ag atoms added as AgNO₃  = 1 mM, N is the number of atoms per NP (from calculation 1), V is the volume of the reaction solution in L, N _A is the Avogadro's number (6.023 × 10²³)

$$\begin{array}{rl}& C=\frac{1\times 6.023\times {10}^{23}}{97561523.7\times 1\times 6.023\times {10}^{23}}\\ & \mathrm{i}.\mathrm{e}.1.0025\times {10}^{-7}\frac{M}{L}=100\mathrm{nM}\end{array}$$

3.5 Antibacterial activity of AgNPs combination with antibiotics

Antibacterial activity of AgNPs along with antibiotics favourably compared with commercial antibiotic disc against pathogenic bacteria by disc diffusion method. The diameter of the inhibition zone around the antibiotic discs combination with or without AgNPs against pathogenic bacterial strains is shown in Tables 2 and 3. AgNPs impregnated with antibiotics exhibit high antibacterial activity than the standard antibiotic disc. The increased antibacterial activities of AgNPs impregnated with the antibiotic disc are shown in Figs. 9 and 10.

Table 2.

Enhanced antibacterial activity of AgNPs against pathogenic bacteria B. subtilis, Bacillus sp. and K. planticola

Bacterial isolates	B. subtilis			Bacillus sp.			K. planticola
	Zone of inhibition, mm
Antibiotics	Ab (a)	Ab+NP (b)	Increase in fold areaa	Ab (a)	Ab+NP (b)	Increase in fold areaa	Ab (a)	Ab + NP (b)	Increase in fold areaa
tetracycline	15	18	0.440	18	19	0.114	21	23	0.200
novobiocin	15	20	0.778	16	20	0.563	18	26	1.086
gentamicin	11	19	1.983	18	20	0.235	19	22	0.341
kanamycin	18	18	0.000	19	20	0.108	21	25	0.417
streptomycin	15	21	0.960	15	24	1.560	16	20	0.563
penicillin	0	7	0.361	0	7	0.361	20	25	0.563
chloramphenicol	25	17	−0.538	21	19	−0.181	32	29	−0.179
ampicillin	0	8	0.778	8	8	0.000	20	16	−0.360
ciprofloxacin	27	22	−0.336	27	23	−0.274	34	23	−0.542

Table 3.

Enhanced antibacterial activity of AgNPs against pathogenic bacteria K. pneumoniae S. nematodiphila and Streptococcus sp

Bacterial isolates	K. pneumoniae			S. nematodiphila			Streptococcus sp.
	Zone of inhibition, mm
Antibiotics	Ab (a)	Ab+NP (b)	Increase in fold areaa	Ab (a)	Ab+NP (b)	Increase in fold areaa	Ab (a)	Ab+NP (b)	Increase in fold areaa
tetracycline	29	32	0.218	13	13	0.000	15	20	0.778
novobiocin	18	25	0.929	0	12	3.000	15	18	0.440
gentamicin	25	27	0.166	17	21	0.526	19	24	0.596
kanamycin	21	30	1.041	19	22	0.341	18	20	0.235
streptomycin	16	22	0.891	13	8	−0.621	16	22	0.891
penicillin	36	43	0.427	0	15	5.250	0	10	1.778
chloramphenicol	34	31	−0.169	27	31	0.318	24	20	−0.306
ampicillin	38	39	0.153	15	22	1.151	0	10	1.778
ciprofloxacin	31	29	−0.125	40	32	−0.360	27	23	−0.274

^a Increased fold area calculated by using b ² −a ² /a ².

Ab – antibiotics.

Ab+NP – antibiotics+AgNPs

Fig. 9.

Enhanced antibacterial activity of AgNPs impregnated with antibiotic discs against B. subtilis, Bacillus sp. and K. planticola

Fig. 10.

Enhanced antibacterial activity of AgNPs impregnated with antibiotic discs against K. pneumoniae, S. nematodiphila and Streptococcus sp.

In this present scenario quite interestingly, B. subtilis and S. nematodiphila were resistant to the commercial antibiotics disc penicillin and ampicillin which is sensitive to antibiotics combination with AgNPs. The enhanced synergistic antibacterial effect was highly observed against Bacillus sp., K. pneumonia and Streptococcus sp. The synergistic antibacterial effect with the combination of AgNPs with antibiotics has more potential activity against Bacillus sp., K. planticola, S. nematodiphila, Streptococcus sp., K. pneumoniae and B. subtilis. This result clearly shows that antibiotic resistant bacteria were highly sensitive to the AgNPs impregnated antibiotic discs. This increased synergistic antibacterial activity may be due to the highly bonding between the antibiotics and AgNPs. Antibacterial activity mainly depended on the size and surface area property of NPs. Small size NPs exhibit large surface area strongly affinity with antibiotics by chelation [64, 65], while it comes in contact with the cell wall of bacteria inhibiting the cross‐links in the membrane leading to cell lysis [23, 25, 66]. Similarly, Geoprincy et al. [67] synthesised the AgNPs impregnated antibiotic discs and accessed the antibacterial activity against Bacillus cereus, B. subtilis, K. Pneumoniae and Vibrio cholera; they have to find that the Ag impregnated antibiotics exhibit fine antibacterial activity when compared with Ag NPs and antibiotics.

4 Conclusion

In this paper, we have demonstrated that eco‐friendly and facile synthesis of AgNPs using a polysaccharide compound i.e. fucoidan which is extracted from P. tertastomatica. AgNPs synthesis was initially identified by stable brown colour and the surface plasmon resonance band was formed at 450 nm. Spherical and the average size of NPs found to be 17 nm. The crystalline structure of synthesised AgNPs was confirmed by SAED and XRD patterns. Herein, AgNPs showed remarkable antibacterial activity against pathogenic organisms; these organisms are resistant to some antibiotics. AgNPs enhanced the antibacterial activity of antibiotics. Microorganisms were attained resistant while treating antibiotics due to long‐time exposure. Hence, there is a need to development of antibacterial agents. This present investigation shows AgNPs have the potential to enhance the antibacterial activity of antibiotics and plays a promising role in the medical field. However fucoidan‐mediated synthesised AgNPs used as an antibacterial agent can eliminate the use of chemical antibiotics agent and it is highly effective, biocompatible and cost‐effective in the biomedical applications.