Green synthesis of silver nanoparticles by Conocarpus Lancifolius plant extract and their antimicrobial and anticancer activities

Due to drug addiction and the emergence of antibiotic resistance in pathogens, the disease load and medication intake have risen worldwide. The alternative treatment for drug-resistant infections is Nano formulation-based antimicrobial agents. The plant extract of Conocarpus Lancifolius fruits was used to synthesize silver nanoparticles in the current study, and it was further employed as an antimicrobial and anticancer agent. Nanoparticles have been characterized by UV–visible spectrometer revealed the notable peak of λ_max = 410–442 nm, which confirms the reduction of silver ion to elemental silver nanoparticles, and the biological moieties in the synthesis were further confirmed by FTIR analysis. The stability and crystalline nature of materials were approved by XRD analysis and expected the size of the nanomaterials of 21 to 173 nm analyzed by a nanophox particle-size analyzer. In vitro, synthesized materials act as an antibacterial agent against Streptococcus pneumonia and Staphylococcus aureus. The inhibition zones of 18 and 24 mm have been estimated to be antibacterial activity against both bacteria. The potency of up to 100% of AgNPs for bacterial strains was incubated overnight at 60 μg/ml. Based on our results, biogenic AgNPs reveal significant activity against fungal pathogen Rhizopusus stolonifera and Aspergillus flavus that cause leading infectious diseases. Additionally, nanomaterials were biocompatible and demonstrated the potential anticancer activities against MDA MB-231 cells after 24-hour exposure.     

Analysis of antimicrobial silver nanoparticles synthesized by coastal strains of Escherichia coli and Aspergillus niger

The present study investigated the extracellular biosynthesis of antimicrobial silver nanoparticles by Escherichia coli AUCAS 112 and Aspergillus niger AUCAS 237 derived from coastal mangrove sediment of southeast India. Both microbial species were able to produce silver nanoparticles, as confirmed by X-ray diffraction spectrum. The nanoparticles synthesized were mostly spherical, ranging in size from 5 to 20 nm for E. coli and from 5 to 35 nm for A. niger, as evident by transmission electron microscopy. Fourier transform spectroscopy revealed prominent peaks corresponding to amides I and II, indicating the presence of a protein for stabilizing the nanoparticles. Electrophoretic analysis revealed the presence of a prominent protein band with a molecular mass of 45 kDa for E. coli and 70 kDa for A. niger. The silver nanoparticles inhibited certain clinical pathogens, with antibacterial activity being more distinct than antifungal activity. The antimicrobial activity of E. coli was more pronounced than that of A. niger and was enhanced with the addition of polyvinyl alcohol as a stabilizing agent. This work highlighted the possibility of using microbes of coastal origin for synthesis of antimicrobial silver nanoparticles.     

Rapid biosynthesis of PVP coated silver nanoparticles by <Emphasis Type="Italic">Kocuria rosea</Emphasis> and their antimicrobial activity

The need for more effective antimicrobial agent and propitious application of nanotechnology in therapeutics and diagnostics has prompted the research on ecofriendly synthesis of silver nanoparticles. The objective of present study was to investigate the antibacterial and antifungal activity of biologically synthesized silver nanoparticles. The silver nanoparticles were synthesized by extracellular method, using soil bacteria Kocuria rosea. The synthesized silver nanoparticles were characterized by UV-Visible spectroscopy, X-ray diffractometry (XRD), transmission electron microscopy (TEM) and fourier transformation infrared spectroscopy (FTIR). On the basis of TEM analysis, the synthesized nanoparticles were found to be spherical with an average size of 30–50 nm. The biologically synthesized silver nanoparticles showed significant antimicrobial activity against pathogens.     

Synthesis of silver nanoparticles by endosymbiont Pseudomonas fluorescens CA 417 and their bactericidal activity

The present study emphasizes on biogenic synthesis of silver nanoparticles and their bactericidal activity against human and phytopathogens. Nanoparticle synthesis was performed using endosymbiont Pseudomonas fluorescens CA 417 inhabiting Coffea arabica L. Synthesized nanoparticles were characterized using hyphenated spectroscopic techniques such as UV–vis spectroscopy which revealed maximum absorption 425 nm. Fourier transform infrared spectroscopy (FTIR) analysis revealed the possible functional groups mediating and stabilizing silver nanoparticles with predominant peaks occurring at 3346 corresponding to hydroxyl group, 1635 corresponding carbonyl group and 680 to aromatic group. X-ray diffraction (XRD) analysis revealed the Bragg’s diffraction pattern with distinct peaks at 38° 44°, 64° and 78° revealing the face-centered cubic (fcc) metallic crystal corresponding to the (111), (200), (220) and (311) facets of the crystal planes at 2θ angle. The energy dispersive X-ray spectroscopy (EDS) analysis revealed presence of high intense absorption peak at 3 keV is a typical characteristic of nano-crystalline silver which confirmed the presence of elemental silver. TEM analysis revealed the size of the nanoparticles to be in the range 5–50 nm with polydisperse nature of synthesized nanoparticles bearing myriad shapes. The particle size determined by Dynamic light scattering (DLS) method revealed average size to be 20.66 nm. The synthesized silver nanoparticles exhibited significant antibacterial activity against panel of test pathogens. The results showed Klebsiella pneumoniae (MTCC 7407) and Xanthomonas campestris to be more sensitive among the test human pathogen and phyto-pathogen respectively. The study also reports synergistic effect of silver nanoparticles in combination with kanamycin which displayed increased fold activity up to 58.3% against Klebsiella pneumoniae (MTCC 7407). The results of the present investigation are promising enough and attribute towards growing scientific knowledge on development of new antimicrobial agents to combat drug resistant microorganisms. The study provides insight on emerging role of endophytes towards reduction of metal salts to synthesize nanoparticles.     

Silver Nanoparticles Toxicity and Bactericidal Effect Against Methicillin-Resistant Staphylococcus aureus: Nanoscale Does Matter

Silver nanoparticles, which are being used increasingly as antimicrobial agents, may extend its antibacterial application to methicillin-resistant Staphylococcus aureus (MRSA), the main cause of nosocomial infections worldwide. To explore the antibacterial properties of silver nanoparticles against MRSA, the present work includes an analysis of the relation between nanosilver effect and MRSA’s resistance mechanisms, a study of the size dependence of the bactericidal activity of nanosilver and a toxicity assessment of nanoparticles against epithelial human cells. Minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and MBC/MIC ratio of silver nanoparticles were quantified by using a luciferase-based assay. The cytotoxic effect (CC₅₀ and CC₉₀) of three different nanosilver sizes (10, 30–40, and 100 nm) were assessed in HeLa cells by a similar method. The therapeutic index was used as an indicator of nanosilver overall efficacy and safety. Silver nanoparticles inhibited bacterial growth of both MRSA and non-MR S. aureus in a bactericidal rather than a bacteriostatic manner (MBC/MIC ratio?≤?4). Silver nanoparticle’s therapeutic index varied when nanoparticle’s size diminished. At the same dose range, 10 nm nanoparticles were the most effective since they did not affect HeLa’s cell viability while inhibiting a considerable percentage of MRSA growth. Silver nanoparticles are effective bactericidal agents that are not affected by drug-resistant mechanisms of MRSA. Nanosilver size mediates MRSA inhibition and the cytotoxicity to human cells, being smaller nanoparticles the ones with a better antibacterial activity and nontoxic effect.     

Biologically produced nanosilver: Current state and future perspectives

Silver nanoparticles are one of the most commercialized nanomaterials. They are widely applied as biocides for their strong antimicrobial activity, but also their conductive, optic and catalytic properties make them wanted in many applications. The chemical and physical processes which are used to synthesize silver nanoparticles generally have many disadvantages and are not eco‐friendly. In this review, we will discuss biological alternatives that have been developed using microorganisms or plants to produce biogenic silver. Until now, only their antimicrobial activity has been studied more into detail. In contrast, a wide range of practical applications as biocide, biosensor, and catalyst are still unexplored. The shape, size, and functionalization of the nanoparticles is defined by the biological system used to produce the nanoparticles, hence for every application a specific biological production process needs to be chosen. On the other hand, biogenic silver needs to compete with chemically produced nanosilver on the market. Large scale production generating inexpensive nanoparticles is needed. This can only be achieved when the biological production system is chosen in function of the yield. Hence, the true challenge for biogenic silver is finding the balance between scalability, price, and applicability. Biotechnol. Bioeng. 2012; 109: 2422–2436. © 2012 Wiley Periodicals, Inc.     

A Method of Obtaining Silver–Succinyl Chitosan Nanocomposites and their Antimicrobial Activity

To form silver nanoparticles by reduction from metal ions in the presence of a reducing agent, D-glucose, a water-soluble derivative of chitosan, succinyl-chitosan, was used as a polymer matrix at room temperature. The synthesis of silver nanoparticles can also be carried out without a reducing agent by thermal activation of the system using an alkali (NaOH) as an accelerator. The presence of silver nanoparticles in the obtained colloidal solutions was judged by the appearance of an absorption band in the electron plasmon resonance spectra (?_max = 417 nm). It has been shown that the use of an additional component, polyethylene oxide, in a macromolecular system makes it possible to obtain small silver nanoparticles (1–3 nm). The results of in vitro studies of the antimicrobial activity of the obtained colloidal solutions containing silver nanoparticles confirm that a decrease in the size of silver nanoparticles leads to an expansion of the spectrum of antibacterial activity of strains of gram-positive and gram-negative bacteria (B. subtilis ATCC 6633, S. aureus 209P, E. coli ATCC 25922) and to the manifestation of a pronounced antifungal action in relation to A. niger INA 00760.

     

The inhibitory activity of typified propolis against Enterococcus species

Propolis, a natural bee product widely used for its antimicrobial activity, was tested against isolates of Enterococcus from humans, pig-tailed macaques, isolates of refractory endodontic treatment cases, and isolates from Lactobacillus-containing food supplements. Typification of the propolis was performed by high-performance liquid chromatography (HPLC) by which prenylated compounds, cinnamic acid derivatives, and flavonoids were detected as the main constituents. Minimum inhibitory concentrations (MIC) were determined using the agar dilution method. All human and animal Enterococcus isolates demonstrated MIC values of 1600 microg/mL. Enterococcal species of human and animal origin were inhibited by propolis. Particularly, human isolates of E. faecium and E. faecalis of refractory endodontic treatment cases were susceptible to propolis of Brazilian origin.     

Antibacterial Activity of Green Synthesized Silver Nanoparticles Using Vasaka (Justicia adhatoda L.) Leaf Extract

There is an increasing demand for silver nanoparticles due to its wide applicability in various area of biological science such as in field of antimicrobial and therapeutics, biosensing, drug delivery etc. To use in bioprocess the silver nanoparticles should be biocompatible and free from toxic chemicals. In the present study we report a cost effective and environment friendly route for green synthesis of silver nanoparticles using Vasaka (Justicia adhatoda L.) leaf extract as reducing as well as capping agent. This plant has been opted for the present study for its known medicinal properties and it is easily available. The biosynthesized silver nanoparticles are characterized by UV–Vis spectroscopy and TEM analysis. It is observed the nanoparticles are well shaped and the average particle size is 20 nm in the range of 5–50 nm. The antibacterial activity of these nanoparticles against Pseudomonas aeruginosa MTCC 741 has been measured by disc diffusion method, agar cup assay and serial dilution turbidity measurement assay. The results show green synthesized silver nanoparticles, using Vasaka leaf extract, have a potential to inhibit the growth of bacteria.

Electronic supplementary material

The online version of this article (doi:10.1007/s12088-015-0512-1) contains supplementary material, which is available to authorized users.     

Characterization of silver nanoparticles synthesized by using marine isolate Streptomyces albidoflavus

Silver nanoparticles production by the green chemistry approach was investigated using an isolated marine actinomycetes strain. The isolated strain was identified as Streptomyces albidoflavus based on chemotaxonomic and ribotyping properties. The strain revealed production of silver nanoparticles both extracellular and intracellularly. Surface Plasmon Resonance analysis with the function of time revealed that particle synthesis by this strain is reaction time dependent. The produced particles were spherical shaped and monodispersive in nature and showed a single surface plasmon resonance peak at 410 nm. Size distribution histograms indicated production of 10-40- nm-size nanoparticles with a mean size of 14.5 nm. FT-IR spectra of nanopartilces showed N-H, C-H, and C-N stretching vibrations, denoting the presence of amino acid/ peptide compounds on the surface of silver nanoparticles produced by S. albidoflavus. Synthesized nanoparticles revealed a mean negative zeta potential and electrophoretic mobility of -8.5 mV and -0.000066 cm2/Vs, respectively. The nanoparticles produced were proteinaceous compounds as capping agents with -8.5 mV zeta potential and revealed antimicrobial activity against both Gram-negative and -positive bacterial strains. Owing to their small size, these particles have greater impact on industrial application spectra.     

Synthesis and characterization of cysteine functionalized silver nanoparticles for biomolecule immobilization

A facile method for the aqueous phase synthesis of cysteine-functionalized silver nanoparticles by potato extract has been reported in the present work. These functionalized nanoparticles were then used for the covalent immobilization of a biomolecule, alkaline phosphatase, on its surface through carbodiimide coupling. Different reaction parameters such as cysteine concentration, reducing agent concentration, temperature, pH and reaction time were varied during the nanoparticles’ formation, and their effects on plasmon resonance were studied using Ultraviolet–visible spectroscopy. Fourier transform infrared spectroscopy was used to confirm the surface modification of silver nanoparticles by cysteine and the particle size analysis was done using particle size analyzer, which showed the average nanoparticles’ size of 61 nm for bare silver nanoparticles and 201 nm for the enzyme-immobilized nanoparticles. The synthesized nanoparticles were found to be highly efficient for the covalent immobilization of alkaline phosphatase on its surface and retained 67 % of its initial enzyme activity (9.44 U/mg), with 75 % binding efficiency. The shelf life of the enzyme-nanoparticle bioconjugates was found to be 60 days, with a 12 % loss in the initial enzyme activity. With a simple synthesis strategy, high immobilization efficiency and enhanced stability, these enzyme-coated nanoparticles have the potential for further integration into the biosensor technology.     

Cellular proliferation/cytotoxicity and antimicrobial potentials of green synthesized silver nanoparticles (AgNPs) using Juniperus procera

Juniperus spp. are used as medicinal plants in many countries like Bosnia, Lebanon, and Turkey. In folk medicines, these plants have been used for treating skin and respiratory tract diseases, urinary problems, rheumatism and gall bladder stones. The objectives of this work were to synthesize silver nanoparticles (AgNPs) using a coniferous tree, Juniperus procera leaf extract and testing the synthesized AgNPs for its antimicrobial potentials, hemolytic activity, toxicity and the proliferative effects against normal and activated rat splenic cells. Leaf extract was prepared using acetone and ethanol as solvents. AgNPs were prepared using the acetone extract. AgNPs were validated using UV–Vis spectroscopy and scanning electron microscopy (SEM). Functional groups in the extract were identified using Fourier Transform Infrared (FT-IR) spectroscopy. SEM images of AgNPs showed spherical and cubic shapes with a uniform size distribution with an average size of 30–90 nm. FT-IR spectroscopy showed the presence of many functional groups in the plant extract. AgNPs showed promising antimicrobial activity against tested bacteria and fungus. AgNPs also expressed a stimulating activity towards the rat splenic cells in a dose dependent manner. Acetone as solvent was safer on cells than ethanol. Green synthesized AgNPs using J. procera might be used as a broad-spectrum therapeutic agent against microorganisms and as an immunostimulant agent.     

Antimicrobial activity of stable silver nanoparticles of a certain size

Conditions for obtaining stable silver nanoparticles smaller than 10 nm were developed using a binary stabilizer polyvinylpyrrolidone/sodium dodecylsulphate in optimal ratio. Optical spectra, morphology and dependence of size of the nanoparticles on the amount of reducing agent were studied. Colloidal solutions of nanosilver showed a high bactericidal activity against strains of Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa, and fungicidal activity against Candida albicans. The mechanism of action of nanosized silver on microbial cell was examined by laser scanning confocal microscope using fluorescent label. First step of antimicrobial effect on microorganisms was membrane damage and penetration of silver nanoparticles into the cell. Prolonged stability of nanoparticles and their antimicrobial activity over the past two years were showed.     

Application of statistical experimental design for optimization of silver nanoparticles biosynthesis by a nanofactory Streptomyces viridochromogenes

Central composite design was chosen to determine the combined effects of four process variables (AgNO₃ concentration, incubation period, pH level and inoculum size) on the extracellular biosynthesis of silver nanoparticles (AgNPs) by Streptomyces viridochromogenes. Statistical analysis of the results showed that incubation period, initial pH level and inoculum size had significant effects (P<0.05) on the biosynthesis of silver nanoparticles at their individual level. The maximum biosynthesis of silver nanoparticles was achieved at a concentration of 0.5% (v/v) of 1 mM AgNO₃, incubation period of 96 h, initial pH of 9 and inoculum size of 2% (v/v). After optimization, the biosynthesis of silver nanoparticles was improved by approximately 5-fold as compared to that of the unoptimized conditions. The synthetic process of silver nanoparticle generation using the reduction of aqueous Ag+ ion by the culture supernatants of S. viridochromogenes was quite fast, and silver nanoparticles were formed immediately by the addition of AgNO₃ solution (1 mM) to the cell-free supernatant. Initial characterization of silver nanoparticles was performed by visual observation of color change from yellow to intense brown color. UV-visible spectrophotometry for measuring surface plasmon resonance showed a single absorption peak at 400 nm, which confirmed the presence of silver nanoparticles. Fourier Transform Infrared Spectroscopy analysis provided evidence for proteins as possible reducing and capping agents for stabilizing the nanoparticles. Transmission Electron Microscopy revealed the extracellular formation of spherical silver nanoparticles in the size range of 2.15–7.27 nm. Compared to the cell-free supernatant, the biosynthesized AgNPs revealed superior antimicrobial activity against Gram-negative, Gram-positive bacterial strains and Candida albicans.     

Silver nanoparticles from Prosopis glandulosa and their potential application as biocontrol of Acinetobacter calcoaceticus and Bacillus cereus

In the present study the characterization and properties of silver nanoparticles from Prosopis glandulosa leaf extract (AgNPs) were investigated using UV–Vis spectroscopic techniques, energy dispersive X-ray spectrometers (EDS), zeta potential and dynamic light scattering. The UV–Vis spectroscopic analysis showed the absorbance peaked at 487 nm, which indicated the synthesis of silver nanoparticles. The experimental results showed silver nanoparticles had Z-average diameter of 421 nm with higher stability (?200 mV). The EDS analysis also exhibited presentation of silver element. Additionally, the different concentrations of AgNPs (25, 50, 75 and 100 mg/mL) showed antibacterial activity against Acinetobacter calcoaceticus and Bacillus cereus. Finally, AgNPs from leaf extracts of P. glandulosa may be used as an agent of biocontrol of microorganism of importance medical. However, further studies will be needed to fully understand the antimicrobial activity of silver nanoparticles obtain from P. glandulosa.     

Synthesis of methylcellulose-silver nanocomposite and investigation of mechanical and antimicrobial properties

In this paper we reported preparation of methylcellulose-silver nanocomposite films by mixing of aqueous solution of methylcellulose with silver nitrate followed by casting. The silver nanoparticles were generated in methylcellulose matrix through reduction and stabilization by methylcellulose. The surface plasmon band at 412nm indicated the formation of Ag nanoparticles. The MC-Ag nanocomposite films were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and Fourier transform infrared (FTIR). The X-ray diffraction analysis of synthesized MC-Ag nanocomposite films revealed that metallic silver was present in face centered cubic crystal structure. Average crystallite size of silver nanocrystal was 22.7nm. The FTIR peaks of as-synthesized MC-Ag nanocomposite fully designated the strong interaction between Ag nanoparticles and MC matrix. Nano-sized silver modified methylcellulose showed enhanced mechanical properties i.e. the introduction of Ag leading to both strengthening and toughening of MC matrix. The methylcellulose-silver nanocomposite films offered excellent antimicrobial activity against various microorganisms.     

The effect of temperature on antibacterial activity of biosynthesized silver nanoparticles

The purpose of this study was the evaluation of two different temperatures on antibacterial activity of the biosynthesized silver nanoparticles. 38 silver nanoparticles-producing bacteria were isolated from soil and identified. Biosynthesis of silver nanoparticles by these bacteria was verified through visible light spectrophotometry. Two strains were relatively active for production of silver nanoparticles. These strains were subjected for molecular identification and recognized as Bacillus sp. and Acinetobacter schindleri. In the present study, the effect of temperatures was evaluated on structure and antimicrobial properties of the silver nanoparrticles by transmission electron microscopy (TEM), X-ray diffraction (XRD) analysis and antimicrobial Agar well diffusion methods. The silver nanoparticles showed antibacterial activity against all the pathogenic bacteria; however, this property was lost after treatment of the silver nanoparticles by high temperatures (100 and 300 °C). TEM images showed that the average sizes of heated silver nanoparticles were >100 nm. However, these were <100 nm for non-heated silver nanoparticles. Although, XRD patterns showed the crystalline structure of heated silver nanoparticles, their antibacterial activities were less. This was possible because of the sizes and accordingly less penetration of the particles into the bacterial cells. In addition, elimination of the capping agents by heat might be considered another reason.     

Silver glyconanoparticles functionalized with sugars of sweet sorghum syrup as an antimicrobial agent

Bio-directed synthesis of metal nanoparticles is gaining importance due to their biocompatibility, low toxicity and eco-friendly nature. We used sweet sorghum syrup for a facile and cost-effective green synthesis of silver glyconanoparticles. Silver nanoparticles were formed due to reduction of silver ions when silver nitrate solution was treated with sorghum syrup solutions of different pH values. The nanoparticles were characterized by UV–vis, TEM (transmission electron microscopy), DLS (dynamic light scattering), EDAX (energy dispersive X-ray spectroscopy), FT-IR (fourier transform infrared spectroscopy) and XRD (X-ray diffraction spectroscopy). The silver glyconanoparticles exhibited a characteristic surface plasmon resonance around 385 nm. At pH 8.5, the nanoparticles were mono-dispersed and spherical in shape with average particle size of 11.2 nm. The XRD and SAED studies suggested that the nanoparticles were crystalline in nature. EDAX analysis showed the presence of elemental silver signal in the synthesized glyconanoparticles. FT-IR analysis revealed that glucose, fructose and sucrose present in sorghum syrup acted as capping ligands. Silver glyconanoparticles prepared at pH 8.5 had a zeta potential of ?28.9 mV and were anionic charged. They exhibited strong antimicrobial activity against Gram-positive, Gram-negative and different Candida species at MIC values ranging between 2 and 32 μg ml^?1. This is first report on sweet sorghum syrup sugars-derived silver glyconanoparticles with antimicrobial property.     

Dual immobilization of biomolecule on the glass surface using cysteine as a bifunctional linker

A novel method for highly efficient enzyme immobilization on the glass surface, by incorporating cysteine as a linker has been demonstrated. The internal glass surface of test tube was pretreated with (3-mercaptopropyl) trimethoxysilane sol–gel and cysteine capped silver nanoparticles, to generate a cysteine layer. This, cysteine rich surface is then used to covalently immobilize alkaline phosphatase on both groups (amino and carboxyl) of cysteine through carbodiimide and glutaraldehyde treatment. The cysteine capped silver nanoparticles were synthesized with an average nanoparticle size of 61 nm as determined by particle size analyzer, while cysteine capping of nanoparticles was confirmed by Fourier transform infra-red spectroscopy. Enhanced enzymatic activity of about 73% was obtained using the dual immobilization technique, while 40% enzyme activity was recovered with carboxyl group and 51% with amino group only. The re-usability of the enzyme immobilized test tube was found to be 8 times and the enzyme retained 85% of its initial activity. With such high immobilization efficiency, cysteine provides a new approach for enhanced immobilization and its integration into different industrial processes and biosensor technology.     

Propolis characterization and antimicrobial activities against Staphylococcus aureus and Candida albicans: A review

Propolis is a plant-based sticky substance that is produced by honeybees. It has been used traditionally by ancient civilizations as a folk medicine, and is known to have many pharmaceutical properties including antioxidant, antibacterial, antifungal, anti-inflammatory, antiviral, and antitumour effects. Worldwide, researchers are still studying the complex composition of propolis to unveil its biological potential, and especially its antimicrobial activity against a variety of multidrug-resistant microorganisms. This review explores scientific reports published during the last decade on the characterization of different types of propolis, and evaluates their antimicrobial activities against Staphylococcus aureus and Candida albicans. Propolis can be divided into different types depending on their chemical composition and physical properties associated with geographic origin and plant sources. Flavonoids, phenols, diterpenes, and aliphatic compounds are the main chemicals that characterize the different types of propolis (Poplar, Brazilian, and Mediterranean), and are responsible for their antimicrobial activity. The extracts of most types of propolis showed greater antibacterial activity against Gram-positive bacteria: particularly on S. aureus, as well as on C. albicans, as compared to Gram-negative pathogens. Propolis acts either by directly interacting with the microbial cells or by stimulating the immune system of the host cells. Some studies have suggested that structural damage to the microorganisms is a possible mechanism by which propolis exhibits its antimicrobial activity. However, the mechanism of action of propolis is still unclear, due to the synergistic interaction of the ingredients of propolis, and this natural substance has multi-target activity in the cell. The broad-spectrum biological potentials of propolis present it as an ideal candidate for the development of new, potent, and cost-effective antimicrobial agents.