Inorganic Nanoparticles: Tools to Emphasize the Janus Face of Amphotericin B

Amphotericin B is the oldest antifungal molecule which is still currently widely used in clinical practice, in particular for the treatment of invasive diseases, even though it is not devoid of side effects (particularly nephrotoxicity). Recently, its redox properties (i.e., both prooxidant and antioxidant) have been highlighted in the literature as mechanisms involved in both its activity and its toxicity. Interestingly, similar properties can be described for inorganic nanoparticles. In the first part of the present review, the redox properties of Amphotericin B and inorganic nanoparticles are discussed. Then, in the second part, inorganic nanoparticles as carriers of the drug are described. A special emphasis is given to their combined redox properties acting either as a prooxidant or as an antioxidant and their connection to the activity against pathogens (i.e., fungi, parasites, and yeasts) and to their toxicity. In a majority of the published studies, inorganic nanoparticles carrying Amphotericin B are described as having a synergistic activity directly related to the rupture of the redox homeostasis of the pathogen. Due to the unique properties of inorganic nanoparticles (e.g., magnetism, intrinsic anti-infectious properties, stimuli-triggered responses, etc.), these nanomaterials may represent a new generation of medicine that can synergistically enhance the antimicrobial properties of Amphotericin B.

Investigation of Antimicrobial Effects of Polydopamine-Based Composite Coatings

Herein, polydopamine (PDA)-based antimicrobial coatings loaded with silver nanoparticles (Ag NPs) and gentamicin were designed and prepared on glass slides using two different approaches. To our knowledge, this study was performed for the first time with the aim to compare these methods (viz., in situ loading and physical adsorption method) regarding the loading and release behavior of payloads. In one method, gentamicin was in situ loaded on PDA-coated substrates during PDA polymerization followed by Ag NPs immobilization (named as Ag@Gen/PDA); for the second method, Ag NPs and gentamicin were simultaneously loaded onto PDA via physical adsorption by immersing pre-formed PDA coatings into a mixed solution of Ag NPs and gentamicin (named as Ag/Gen@PDA). The loading and release characteristics of these antimicrobial coatings were compared, and both gave variable outcomes. The in situ loading method consequently provided a relatively slow release of loaded antimicrobials, i.e., approx. 46% for Ag@Gen/PDA as compared to 92% from physically adsorbed Ag/GenPDA in an immersion period of 30 days. A similar trend was observed for gentamicin release, i.e., ~0.006 µg/mL from Ag@Gen/PDA and 0.02 µg/mL from Ag/Gen@PDA each day. The slower antimicrobial release from Ag@Gen/PDA coatings would ultimately provide an effective long-term antimicrobial property as compared to Ag/Gen@PDA. Finally, the synergistic antimicrobial activities of these composite coatings were assessed against two microbial species, namely, Staphylococcus aureus and Escherichia coli, hence providing evidence in the prevention of bacterial colonization.

Characterization of Genomic Diversity among Carbapenem-Resistant Escherichia coli Clinical Isolates and Antibacterial Efficacy of Silver Nanoparticles from Pakistan

The emergence of carbapenem-resistant Escherichia coli (E. coli) is considered an important threat to public health resulting in resistance accumulation due to antibiotics misuse and selection pressure. This warrants periodic efforts to investigate and develop strategies for infection control. A total of 184 carbapenem-resistant clinical strains of E. coli were characterized for resistance pattern, resistance genes, plasmids, sequence types and in vitro efficacy of silver nanoparticles (AgNPs). Carbapenem resistance was prevalent in E. coli isolated from female patients (64.7%), urine samples (40.8%) and surgical wards (32.1%). Polymyxin-B showed higher susceptibility. ESBLs and carbapenemases were produced in 179 and 119 isolates, respectively. Carbapenemase-encoding genes were observed among 104 strains with blaNDM-1 (45.1%), blaOXA-48 (27%), blaNDM-7 (3.8%), blaNDM-1/blaOXA-48 (15.4%), blaNDM-7/blaOXA-48 (2.9%), blaOXA-48/blaVIM (3.8%) and blaNDM-1/blaVIM (2%). ESBL resistance genes were detected in 147 isolates, namely blaSHV (24.9%), blaCTX-M (17.7%), blaTEM (4.8%), blaSHV/blaCTX-M (29.2%), blaSHV/blaTEM (15%) and blaCTX-M/blaTEM (8.8%). ST405 (44.4%) and ST131 (29.2%) were more frequent sequence types with ST101 (9.7%), ST10 (9.7%) and ST648 (7%). The replicon types IncFII, IncFIIK, IncA/C, IncN and IncL/M were detected. The combination of MEM/AgNPs remained effective against carbapenemase-positive E. coli. We reported genetically diverse E. coli strains coharboring carbapenemases/ESBLs from Pakistan. Moreover, this study highlights the enhanced antibacterial activity of MEM/AgNPs and may be used to manage bacterial infections.

Silver Nanoparticle-Based Combinations with Antimicrobial Agents against Antimicrobial-Resistant Clinical Isolates

The increasing prevalence of antimicrobial-resistant (AMR) bacteria along with the limited development of antimicrobials warrant investigating novel antimicrobial modalities. Emerging inorganic engineered nanomaterials (ENMs), most notably silver nanoparticles (AgNPs), have demonstrated superior antimicrobial properties. However, AgNPs, particularly those of small size, could exert overt toxicity to mammalian cells. This study investigated whether combining AgNPs and conventional antimicrobials would produce a synergistic response and determined the optimal and safe minimum inhibitory concentration (MIC) range against several wild-type Gram-positive and -negative strains and three different clinical isolates of AMR Klebsiella pneumoniae. Furthermore, the cytotoxicity of the synergistic combinations was assessed in a human hepatocyte model. The results showed that the AgNPs (15-25 nm) were effective against Gram-negative bacteria (MIC of 16-128 µg/mL) but not Gram-positive strains (MIC of 256 µg/mL). Both wild-type and AMR K. pneumoniae had similar MIC values following exposure to AgNPs. Importantly, co-exposure to combinations of AgNPs and antimicrobial agents, including kanamycin, colistin, rifampicin, and vancomycin, displayed synergy against both wild-type and AMR K. pneumoniae isolates (except for vancomycin against AMR strain I). Notably, the tested combinations demonstrated no to minimal toxicity against hepatocytes. Altogether, this study indicates the potential of combining AgNPs with conventional antimicrobials to overcome AMR bacteria.

Antibacterial Activity of Silver Nanoparticles Synthesized by Aspergillus flavus and its Synergistic Effect with Antibiotics

Microbial antibiotic resistance is rapidly increasing as a result of overuse or misuse of antibiotics, as well as a lack of new, effective antibiotics. Alternative antimicrobial treatments, such as nanoparticles, and their potential for stronger synergetic effect when paired with other active chemicals, could be a viable option. This study is prepared to estimate the antibacterial activity of silver nanoparticles (AgNPs) that have been synthesized using the biomass-free filtrate of Aspergillus flavus. The formation of AgNPs was reported by color changed to a dark brownish-black after 72 hours of incubation. The AgNPs surface plasmon resonance peak was indicated in the UV–Vis spectrum at 427 nm. The synthesis of AgNPs with a nanoparticle size of 10 to 35 nm was validated using transmission electron microscopy. The increase in folding area was calculated to detect the synergistic potential of the combined AgNPs with a broad range of conventional antibiotics. AgNPs have broad-spectrum activity against all strains tested. The most sensitive strain was Escherichia coli (11 mm), whereas the most resistant strain was Pseudomonas aeruginosa, as indicated by the lowest inhibition zone (7 mm). The lowest Minimum Inhibitory Concentration indicated was against K. pneumonia and Enterobacter cloacae (0.025 mg/mL, each), followed by Staphylococcus epidermidis (0.05 mg/mL), E. coli and Shigella sp. (0.075 mg/mL, each), and then S. aureus (0.1 mg/mL). Notable synergy was reported between AgNPs and either ampicillin, erythromycin, ceftriaxone, vancomycin, azlocillin, or amoxicillin against S. aureus in the range between 29.3-fold to 8-fold. In addition, synergy was seen between AgNPs and either vancomycin, clindamycin, or erythromycin against P. aeruginosa (31.1-8.0-fold). Also, a maximum increase in IFA when erythromycin and vancomycin were synergized with AgNPs against E. cloacae was reported (IFA of 10.0 and 9.0, respectively). Similarly, AgNPs with either aztreonam or azlocillin against E. coli and amoxicillin, ciprofloxacin, or ceftriaxone against Shigella sp. caused an increase in the fold area of inhibition of between 5.3-3.7-fold. This result may have an advantage in encouraging the use of combined AgNPS with conventional antibiotics in treating infectious diseases caused by antibiotic-resistant bacteria.

Antimicrobial Activity Enhancers: Towards Smart Delivery of Antimicrobial Agents

The development of effective treatments against infectious diseases is an extensive and ongoing process due to the rapid adaptation of bacteria to antibiotic-based therapies. However, appropriately designed activity enhancers, including antibiotic delivery systems, can increase the effectiveness of current antibiotics, overcoming antimicrobial resistance and decreasing the chance of contributing to further bacterial resistance. The activity/delivery enhancers improve drug absorption, allow targeted antibiotic delivery, improve their tissue and biofilm penetration and reduce side effects. This review provides insights into various antibiotic activity enhancers, including polymer, lipid, and silver-based systems, designed to reduce the adverse effects of antibiotics and improve formulation stability and efficacy against multidrug-resistant bacteria.

Evaluation of the wound healing effect of neomycin-silver nano-composite gel in rats

Objectives: Both nano silver and neomycin have wound healing properties. Silver nanoparticles have been used as main compounds for therapeutic drug delivery systems against various ailments. The present study aimed to prepare a neomycin silver nano-composite gel easily, rapidly, and cheaply method to improve wound healing. Methods: Forty-five Wistar rats (150–200 g) divided into nine groups: wound untreated, wound fusidic acid treated, wound neomycin treated, three groups with wound and neomycin silver nano-composite gel at 1:1, 1:2, and 1:3 concentrations, respectively, and three groups wound treated silver nano gel at the previous concentrations, respectively. Percentages of wound healing and histopathological examination of the wound area were assessed in all groups. Results: Atomic force microscopy (AFM) and transmission electron microscopy (TEM) images demonstrated the spherical shape of neomycin silver nano-composite gel without aggregation but homogenous dispersion in a gel matrix. Dynamic light scattering (DLS) showed a 4 nm size of nano silver, which agrees with AFM image data analysis but not with TEM image due to the good coating of the gel matrix to silver nanoparticles. Dynamic light scattering Zeta potential was −21 mV, illustrating the high bioactivity of the neomycin silver nano-composite. The groups receiving neomycin silver nano-composite gel showed a significantly higher and dose dependent wound healing compared to other treatment groups. Conclusion: The present work confirmed the potential wound healing activity of neomycin silver nano-composite gel compared to either alone.

Phytoproduct, Arabic Gum and Opophytum forsskalii Seeds for Bio-Fabrication of Silver Nanoparticles: Antimicrobial and Cytotoxic Capabilities

The application of biological materials in synthesizing nanoparticles has become significant issue in nanotechnology. This research was designed to assess biogenic silver nanoparticles (AgNPs) fabricated using two aqueous extracts of Acacia arabica (Arabic Gum) (A-AgNPs) and Opophytum forsskalii (Samh) seed (O-AgNPs), which were used as reducing and capping agents in the NPs development, respectively. The current study is considered as the first report for AgNP preparation using Opophytum forsskalii extract. The dynamic light scattering, transmission electron microscopy, and scanning electron microscopy were employed to analyze the size and morphology of the biogenic AgNPs. Fourier transform infrared (FTIR) spectroscopy and chromatography/mass spectrometry (GC-MS) techniques were used to identify the possible phyto-components of plant extracts. The phyto-fabricated NPs were assessed for their antibacterial activity and also when combined with some antibiotics against Staphylococcus aureus (Gram-positive) and Pseudomonas aeruginosa and Escherichia coli (Gram-negative) and their anticandidal ability against Candida albicans using an agar well diffusion test. Furthermore, cytotoxicity against LoVo cancer cell lines was studied. The results demonstrated the capability of the investigated plant extracts to change Ag+ ions into spherical AgNPs with average size diameters of 91 nm for the prepared O-AgNPs and 75 nm for A-AgNPs. The phyto-fabricated AgNPs presented substantial antimicrobial capabilities with a zone diameter in the range of 10-29.3 mm. Synergistic effects against all tested strains were observed when the antibiotic and phyto-fabricated AgNPs were combined and assessed. The IC50 of the fabricated O-AgNPs against LoVo cancer cell lines was 28.32 μg/mL. Ten and four chemical components were identified in Acacia arabica (Arabic Gum) and Opophytum forsskalii seed extracts, respectively, by GC-MS that are expected as NPs reducing and capping agents. Current results could lead to options for further research, such as investigating the internal mechanism of AgNPs in bacteria, Candida spp., and LoVo cancer cell lines as well as identifying specific molecules with a substantial impact as metal-reducing agents and biological activities.

A Biological Study of Anisotropic Silver Nanoparticles and Their Antimicrobial Application for Topical Use

The excessive use of antibiotics in both human and veterinary medicine has contributed to the development and rapid spread of drug resistance in bacteria. Silver nanoparticles (AgNPs) have become a tool of choice that can be used to treat these resistant bacteria. Several studies have shown that AgNPs have antibacterial and wound healing properties. In this study, we evaluated the biological activity of anisotropic AgNPs to develop an antimicrobial gel formulation for treating wound infections. We showed that some anisotropic AgNPs (S2) have an effective antibacterial activity against bacterial pathogens and low cytotoxicity to keratinocytes and fibroblasts in vitro. The MIC and MBC values were in the range of 2-32 µg/mL, and cytotoxicity had IC₅₀ values of 68.20 ± 9.71 µg/mL and 68.65 ± 10.97 µg/mL against human keratinocyte and normal human dermal fibroblast cells, respectively. The anisotropic AgNPs (S2) were used as a gel component and tested for antibacterial activity, including long-term protection, compared with povidone iodine, a common antiseptic agent. The results show that the anisotropic AgNPs can inhibit the growth of most tested bacterial pathogens and provide protection longer than 48 h, whereas povidone iodine only inhibits the growth of some bacteria. This study suggests that anisotropic AgNPs could be used as an alternative antimicrobial agent for treating bacterial skin infection and as a wound healing formulation.

Silver Nanoparticles Enhance Antimicrobial Efficacy of Antibiotics and Restore That Efficacy against the Melioidosis Pathogen

Melioidosis is an infectious disease caused by Gram-negative bacillus bacteria Burkholderia pseudomallei. Due to the emerging resistance of B. pseudomallei to antibiotics including ceftazidime (CAZ), the development of novel antibiotics and alternative modes of treatment has become an urgent issue. Here, we demonstrated an ability to synergistically increase the efficiency of antibiotics through their combination with silver nanoparticles (AgNPs). Combinations of four conventional antibiotics including CAZ, imipenem (IMI), meropenem (MER), and gentamicin sulfate (GENT) with starch-stabilized AgNPs were tested for their antibacterial effects against three isolates of B. pseudomallei. The combination of each antibiotic with AgNPs featured fractional inhibitory concentration (FIC) index values and fractional bactericidal concentration (FBC) index values ranging from 0.312 to 0.75 µg/mL and 0.252 to 0.625 µg/mL, respectively, against the three isolates of B. pseudomallei. The study clearly showed that most of the combinatorial treatments exhibited synergistic antimicrobial effects against all three isolates of B. pseudomallei. The highest enhancing effect was observed for GENT with AgNPs. These results confirmed the combination of each antibiotic with AgNPs restored their bactericidal potency in the bacterial strains that had previously been shown to be resistant to the antibiotics. In addition, morphological changes examined by SEM confirmed that the bacterial cells were severely damaged by combinations at the FBC level. Although bacteria produce fibers to protect themselves, ultimately the bacteria were killed by the antibiotic-AgNPs combinations. Overall, these results suggest the study of antibiotic-AgNPs combinations as an alternative design strategy for potential therapeutics to more effectively combat the melioidosis pathogen.

Cracking the Challenge of Antimicrobial Drug Resistance with CRISPR/Cas9, Nanotechnology and Other Strategies in ESKAPE Pathogens

Antimicrobial resistance is mushrooming as a silent pandemic. It is considered among the most common priority areas identified by both national and international agencies. The global development of multidrug-resistant strains now threatens public health care improvement by introducing antibiotics against infectious agents. These strains are the product of both continuous evolution and unchecked antimicrobial usage (AMU). The ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) are the leading cause of nosocomial infections throughout the world. Most of them are now multidrug-resistant, which pose significant challenges in clinical practice. Understanding these bacteria’s resistance mechanisms is crucial for developing novel antimicrobial agents or other alternative tools to fight against these pathogens. A mechanistic understanding of resistance in these pathogens would also help predict underlying or even unknown mechanisms of resistance of other emerging multidrug-resistant pathogens. Research and development to find better antibacterial drugs and research on tools like CRISPER-Cas9, vaccines, and nanoparticles for treatment of infections that can be further explored in the clinical practice health sector have recognized these alternatives as essential and highly effective tools to mitigate antimicrobial resistance. This review summarizes the known antimicrobial resistance mechanisms of ESKAPE pathogens and strategies for overcoming this resistance with an extensive overview of efforts made in this research area.

Nanoparticles for treatment of bovine Staphylococcus aureus mastitis

Staphylococcus aureus (S. aureus) is one of the most important zoonotic bacterial pathogens, infecting human beings and a wide range of animals, in particular, dairy cattle. Globally. S. aureus causing bovine mastitis is one of the biggest problems and an economic burden facing the dairy industry with a strong negative impact on animal welfare, productivity, and food safety. Furthermore, its smart pathogenesis, including facultative intracellular parasitism, increasingly serious antimicrobial resistance, and biofilm formation, make it challenging to be treated by conventional therapy. Therefore, the development of nanoparticles, especially liposomes, polymeric nanoparticles, solid lipid nanoparticles, nanogels, and inorganic nanoparticles, are gaining traction and excellent tools for overcoming the therapeutic difficulty accompanied by S. aureus mastitis. Therefore, in this review, the current progress and challenges of nanoparticles in enhancing the S. aureus mastitis therapy are focused stepwise. Firstly, the S. aureus treatment difficulties by the antimicrobial drugs are analyzed. Secondly, the advantages of nanoparticles in the treatment of S. aureus mastitis, including improving the penetration and accumulation of their payload drugs intracellular, decreasing the antimicrobial resistance, and preventing the biofilm formation, are also summarized. Thirdly, the progression of different types from the nanoparticles for controlling the S. aureus mastitis are provided. Finally, the difficulties that need to be solved, and future prospects of nanoparticles for S. aureus mastitis treatment are highlighted. This review will provide the readers with enough information about the challenges of the nanosystem to help them to design and fabricate more efficient nanoformulations against S. aureus infections.

Bio fabrication of silver nanoparticles with antibacterial and cytotoxic abilities using lichens

Recently, increase bacterial resistance to antimicrobial compounds issue constitutes a real threat to human health. One of the useful materials for bacterial control is Silver nanoparticles (AgNPs). Researchers tend to use biogenic agents to synthesize stable and safe AgNPs. The principal aim of this study was to investigate the ability of lichen in AgNPs formation and to find out their suppression ability to MDR bacteria as well as their cytotoxic activity. In the current study, lichens (Xanthoria parietina, Flavopunctelia flaventior) were collected from the south of the Kingdom of Saudi Arabia. Lichens methanolic extracts were used for conversion of Ag ions to AgNPs. Prepared biogenic AgNPs were characterized by Ultraviolet–Visible (UV–Vis) Spectroscopy, Transmission electron microscopy (TEM), Dynamic Light Scattering (DLS) and Zeta potential and Energy-Dispersive X-ray Spectroscopy (EDS). Lichens Secondary metabolites were determined by Fourier-Transform Infrared Spectroscopy (FTIR) and Gas Chromatography–Mass Spectrometry (GC–MS). The antibacterial activity and synergistic effect of AgNPs were evaluated against pathogenic bacteria, including gram-positive; Methicillin-resistant Staphylococcus aureus (MRSA), Vancomycin-resistant Enterococcus (VRE), and gram-negative; (Pseudomonas aeruginosa, Escherichia coli) as well as the reference strains (ATCC) using the agar disk diffusion method. Cytotoxic effect of biogenic AgNPs was tested against HCT 116 (Human Colorectal Cancer cell), MDA-MB-231 (Breast cancer cell), and FaDu (Pharynx cancer cell) by MTT test. TEM imaging showed well-dispersed spherical particles of 1–40 nm size as well as zeta size showed 69–145 nm. Furthermore, FTIR and GC–MS identified various lichen chemical molecules. On the other hand, the highest antibacterial activity of AgNPs was noticed against P. aeruginosa, followed by MRSA, VRE, and E. coli. AgNPs influence on gram-negative bacteria was greater than that on gram-positive bacteria and their synergistic effect with some antibiotics was noted against examined microbes. Moreover, higher cytotoxicity for biogenic AgNPs against FaDu and HCT 116 cell line in relation to MDA-MB-231 was noted. Given the current findings, the biogenic AgNPs mediated by lichens had positive antibacterial, synergistic and cytotoxic powers. Therefore, they might be considered as a promising candidate to combat the multi-drug resistance organisms and some cancer cells.

The Influence of Different Forms of Silver on Selected Pathogenic Bacteria

The application of silver nanoparticles as an antibacterial agent is becoming more common. Unfortunately, their effect on microorganisms is still not fully understood. Therefore, this paper attempts to investigate the influence of silver ions, biologically synthesized silver nanoparticles and nanoparticles functionalized with antibiotics on molecular bacteria profiles. The initial stage of research was aimed at the mechanism determination involved in antibiotics sorption onto nanoparticles' surface. For this purpose, the kinetics study was performed. Next, the functionalized formulations were characterized by Fourier transform infrared spectroscopy (FT-IR), dynamic light scattering (DLS) and a zeta potential study. The results reveal that functionalization is a complex process, but does not significantly affect the stability of biocolloids. Furthermore, the antimicrobial assays, in most cases, have shown no increases in antibacterial activity after nanoparticle functionalization, which suggests that the functionalization process does not always generate the improved antimicrobial effect. Finally, the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) technique was employed to characterize the changes in the molecular profile of bacteria treated with various antibacterial agents. The recorded spectra proved many differences in bacterial lipids and proteins profiles compared to untreated cells. In addition, the statistical analysis of recorded spectra revealed the strain-dependent nature of stress factors on the molecular profile of microorganisms.

Application of some nanoparticles in the field of veterinary medicine

Nanotechnology is a fast-growing technology that plays an important great impact on various fields of therapeutic applications. It is capable for solving several problems related to animal health and production. There are different nano-systems such as liposomes, metallic nanoparticles, polymeric micelles, polymeric nanospheres, functionalized fullerenes, carbon nanotubes, dendrimers, polymer-coated nanocrystals and nanoshells. In this review, we mentioned different methods for the preparation and characterization of nanoparticles. This review is concerned mainly on nanoparticle systems for antibiotic delivery which suffer from poor bioavailability and many side effects. Nanoparticles are characterized by many features include their minimal size, colossal surface zone to mass extent. The development of antimicrobials in nanoparticle systems is considered an excellent alternative delivery system for antimicrobials for the treatment of microbial diseases by increasing therapeutic effect and overcoming the side effects. In this paper, we reviewed some antimicrobial nanoparticle preparations and we focused on florfenicol and neomycin nanoparticle preparations as well as chitosan and silver nanoparticles preparations to prepare, characterize and compare their different pharmacological effects.

Enhanced bactericidal efficacy of polymer stabilized silver nanoparticles in conjugation with different classes of antibiotics

The paper presents the interaction mechanism of silver nanoparticles (AgNPs) with different antibiotics and the antibacterial efficacy of the formed conjugates. The AgNPs used in this study were synthesized from silver nitrate using sodium borohydride as a reducing agent, in the presence of PVP as a protecting agent. Two antibiotics, amikacin and vancomycin with different modes of action, were used to functionalize the synthesized PVP-capped AgNPs. The formation of antibiotic-AgNPs conjugate was confirmed by UV-vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS) and X-ray diffraction (XRD) and the results suggest the conjugation of both drugs to silver nanoparticle surfaces. FTIR results indicate that intermolecular hydrogen bonding exists between PVP-coated AgNPs and antibiotics. The oxygen atom coordinated with PVP was available for interaction with either amine or amide groups of drugs. Further, the antibacterial efficacy of these PVP-capped AgNPs with selected antibiotics was evaluated against Escherichia coli and Staphylococcus aureus by agar well diffusion test. Synergetic bactericidal activity for antibiotic-AgNPs conjugate was observed against both microbes.

Silver nanoparticles as antimicrobial therapeutics: current perspectives and future challenges

Utility of silver metal in antimicrobial therapy is an accepted practice since ages that faded with time because of the identification of a few silver resistant strains in the contemporary era. A successive development of antibiotics soon followed. However, due to an indiscriminate and unregulated use coupled with poor legal control measures and a dearth of expertise in handling the critical episodes, the antibiotics era has already seen a steep decline in the past decades due to the evolution of multi-drug resistant 'superbugs' which pose a sizeable challenge to manage with. Due to limited options in the pipeline and no clear strategy in the forefront, the aspirations for novel, MDR focused drug discovery to target the 'superbugs' arose which once again led to the rise of AgNPs in antimicrobial research. In this review, we have focused on the green routes for the synthesis of AgNPs, the mode of microbial inhibition by AgNPs, synergistic effect of AgNPs with antibiotics and future challenges for the development of nano-silver-based therapeutics.

Bioinspired and Biomimetic AgNPs/Gentamicin-Embedded Silk Fibroin Coatings for Robust Antibacterial and Osteogenetic Applications

With the progressively increasing demand for orthopedic Ti implants, the balance between two primary complications restricting implant applications is needed to be solved: the lack of bone tissue integration and biomedical device-associated infections (BAI), where emergence of multiresistance bacteria make it worse. Notably, a combination of silver nanoparticles (AgNPs) and a kind of antibiotic can synergistically inhibit bacterial growth, where a low concentration of AgNPs has been confirmed to promote the proliferation and osteogenesis of osteoblasts. In this work, we built AgNPs/gentamicin (Gen)-embedded silk fibroin (SF)-based biomimetic coatings on orthopedic titanium by a facile dipping-drying circular process and with the assistance of polydopamine (PD). Ag⁺ was reduced to AgNPs by SF under ultraviolet (UV) irradiation, and then they were detected by transmission electron microscope (TEM) images and UV-visible (UV-vis) analyses. Intriguingly, the addition of Gen highly improved the reduction efficiency of Ag⁺. The antibacterial efficiency of SF-based coatings was examined by challenging them with pathogenic Staphylococcus aureus (S. aureus) bacteria which produced biofilms, and consequently, we found that low concentration loading, durable release of Ag⁺ (28 days), and 10-fold improvement of antibacterial efficiency were achieved for our novel AgNPs- and Gen-embeded silk fibroin coatings. In bacteria and a cells cocultured system, AgNPs/Gen-embedded coatings strongly inhibited adhesion and proliferation of S. aureus, simultaneously improving cell adhesion and growth. To investigate cytocompatibility and osteogenic potential, different coatings were cultured with MC3T3 cells; AgNPs/Gen-embedded coatings showed generally acceptable biocompatibility (cell adhesion, proliferation, and viability) and accelerated osteoblast maturation (alkaline phosphatase production, matrix secretion, and calcification). Expectantly, this novel biofunctional coating will have promising applications in orthopedic and dental titanium implants thanks to its excellently antibacterial, biocompatible, and osteogenic activities.

Silver nanoparticles from Pilimelia columellifera subsp. pallida SL19 strain demonstrated antifungal activity against fungi causing superficial mycoses

In this study, we present the in vitro antifungal activity of silver nanoparticles (AgNPs) synthesized from acidophilic actinobacterium Pilimelia columellifera subsp. pallida SL19 strain, alone and in combination with antibiotics viz., amphotericin B, fluconazole, and ketoconazole against pathogenic fungi, namely Candida albicans, Malassezia furfur, and Trichophyton erinacei. The minimum inhibitory concentration (MIC) and minimum biocidal concentration (MBC) of AgNPs against test fungi were evaluated. The fractional inhibitory concentration (FIC) index was determined to estimate antifungal activity of AgNPs combined with antibiotics. Antifungal activity of AgNPs varied among the tested fungal strains. M. furfur was found to be most sensitive to biogenic silver nanoparticles, followed by C. albicans and T. erinacei. The lowest MIC of AgNPs was noticed against M. furfur (16 μg ml^-1 ). Synergistic effect was observed on C. albicans when AgNP were combined with amphotericin B and ketoconazole and on M. furfur with fluconazole and ketoconazole (FIC index of 0.5). Cytotoxic effect of AgNPs on HeLa and 3T3 cell lines was evaluated. The IC₅₀ values were found to be 55 and 25 μg ml^-1 , respectively. The present study indicates that silver nanoparticles from P. columellifera subsp. pallida SL19 strain have antifungal activity, both alone and in combination with antibiotics, and offer a valuable contribution to nanomedicine.