Synergistic action of cinnamaldehyde with silver nanoparticles against spore-forming bacteria: a case for judicious use of silver nanoparticles for antibacterial applications

Polyethylenimine as a Versatile Simultaneous Reducing and Stabilizing Agent Enabling One-Pot Synthesis of Transition-Metal Nanoparticles: Fundamental Aspects and Practical Implications

The large surface area of metallic nanoparticles provides them with particular optical, chemical, and biological properties, accordingly enabling their use in a wide array of applications. In this regard, facile and fast synthetic approaches are desirable for ready-to-use functional materials. Following early investigations focused on the direct synthesis of polymer-coated gold nanoparticles, we herein demonstrate that such a strategy can be used to manufacture different types of d-block transition-metal nanoparticles via a one-pot method in aqueous media and mild temperature conditions. Gold (Au3+), palladium (Pd2+), and silver (Ag+) ions could be reduced using only polyethylenimine (PEI) or PEI derivatives acting simultaneously as a reducing and stabilizing agent and without the aid of any other external agent. The process gave rise, for instance, to Pd urchin-like nanostructures with a large surface area which confers to them outstanding catalytic performance compared to AuNPs and AgNPs produced using the same strategy. The polymer-stabilized AgNPs were demonstrated to be biocide against a variety of microorganisms, although AuNPs and PdNPs do not hold such an attribute at least in the probed concentration range. These findings may provide significant advances toward the practical, facile, and ready-to-use manufacturing of transition-metal nanoparticles for a myriad of applications.

Biogenic silver nanoparticles and cinnamaldehyde as an effective sanitizer for fresh sweet grape tomatoes

This study evaluated the antibacterial activity of cinnamaldehyde (CIN) and biogenic silver nanoparticles (BioAgNP), alone and in combination, against Escherichia coli, Salmonella Typhimurium, and Staphylococcus aureus in vitro. Their sanitation activities on fresh sweet grape tomatoes were also evaluated. CIN and BioAgNP inhibited the growth of the tested bacteria, and at low concentrations, their combinations presented a synergistic effect. In the sanitization of fresh sweet grape tomatoes, CIN (156 µg/mL) combined with BioAgNP (31.25 µM) at subinhibitory concentrations inhibited the growth of E. coli after only 5 min of contact. Exposed samples showed no growth of E. coli during their shelf life. The combination of these compounds did not change significantly (p > 0.05) the physicochemical properties of sweet grape tomatoes and showed that CIN combined with BioAgNP could represent an effective method for decontaminating fruits and vegetables. This combination has great potential for application in the prevention of foodborne diseases.

Fabrication of Gold Nanoparticles and Cinnamaldehyde-Functionalized Paper-Based Films and Their Antimicrobial Activities against White Film-Forming Yeasts

During storage and fermentation of kimchi, white film-forming yeasts (WFY) are generated on the surface of kimchi under various conditions. These yeasts include Candida sake, Pichia kudriavzevii, Kazachstania servazzii, Debaryomyces hansenii, and Hanseniaspora uvarum. Because of the off-odor and texture-softening properties of WFY that degrade the quality of kimchi, a method to prevent WFY is required. In this study, cinnamaldehyde (CIN) and gold nanoparticles (AuNPs) with a large surface area were grafted on a paper surface, which was termed the "Paper_AuNPs_CIN" film. CIN is an antimicrobial agent that is approved for use in food applications. In the as-fabricated Paper_AuNPs_CIN film, antimicrobial CIN molecules were physically adsorbed to the surface of AuNPs and simultaneously chemically synthesized on the paper surface via the imine reaction. The Paper_AuNPs_CIN film exhibited greater antimicrobial activity against the three WFY strains than a Paper_CIN film (which contains only CIN molecules). Since more CIN molecules were adsorbed to the large surface area of the paper-reduced AuNPs, the Paper_AuNPs_CIN film exhibited a higher antimicrobial activity. Using AuNPs and CIN simultaneously to inhibit the growth of WFY is a novel approach that has not yet been reported. The morphology and elemental mapping of the functionalized films were examined via scanning electron microscopy and energy-dispersive spectroscopy, elemental composition was analyzed via inductively coupled plasma optical emission spectroscopy, and chemical bonding and optical properties were investigated via Fourier transform infrared spectroscopy and diffuse reflectance spectroscopy. Additionally, agar-well diffusion assays were used to determine the antimicrobial activity against three representative WFY strains: C. sake, P. kudriavzevii, and K. servazzii.

Essential Oils Encapsulated in Zeolite Structures as Delivery Systems (EODS): An Overview

Essential oils (EO) obtained from plants have proven industrial applications in the manufacturing of perfumes and cosmetics, in the production and flavoring of foods and beverages, as therapeutic agents in aromatherapy, and as the active principles or excipients of medicines and pharmaceutics due to their olfactory, physical-chemical, and biological characteristics. On behalf of the new paradigm of a more natural and sustainable lifestyle, EO are rather appealing due to their physical, chemical, and physiological actions in human beings. However, EO are unstable and susceptible to degradation or loss. To tackle this aspect, the encapsulation of EO in microporous structures as zeolites is an attractive solution, since these host materials are cheap and non-toxic to biological environments. This overview provides basic information regarding essential oils, including their recognized benefits and functional properties. Current progress regarding EO encapsulation in zeolite structures is also discussed, highlighting some representative examples of essential oil delivery systems (EODS) based on zeolites for healthcare applications or aromatherapy.

Design strategies for adhesive hydrogels with natural antibacterial agents as wound dressings: Status and trends

The wound healing process is usually susceptible to different bacterial infections due to the complex physiological environment, which significantly impairs wound healing. The topical application of antibiotics is not desirable for wound healing because the excessive use of antibiotics might cause bacteria to develop resistance and even the production of super bacteria, posing significant harm to human well-being. Wound dressings based on adhesive, biocompatible, and multi-functional hydrogels with natural antibacterial agents have been widely recognized as effective wound treatments. Hydrogels, which are three-dimensional (3D) polymer networks cross-linked through physical interactions or covalent bonds, are promising for topical antibacterial applications because of their excellent adhesion, antibacterial properties, and biocompatibility. To further improve the healing performance of hydrogels, various modification methods have been developed with superior biocompatibility, antibacterial activity, mechanical properties, and wound repair capabilities. This review summarizes hundreds of typical studies on various ingredients, preparation methods, antibacterial mechanisms, and internal antibacterial factors to understand adhesive hydrogels with natural antibacterial agents for wound dressings. Additionally, we provide prospects for adhesive and antibacterial hydrogels in biomedical applications and clinical research.

Biogenic Silver Nanoparticles Strategically Combined With Origanum vulgare Derivatives: Antibacterial Mechanism of Action and Effect on Multidrug-Resistant Strains

Multidrug-resistant bacteria have become a public health problem worldwide, reducing treatment options against several pathogens. If we do not act against this problem, it is estimated that by 2050 superbugs will kill more people than the current COVID-19 pandemic. Among solutions to combat antibacterial resistance, there is increasing demand for new antimicrobials. The antibacterial activity of binary combinations containing bioAgNP (biogenically synthesized silver nanoparticles using Fusarium oxysporum), oregano essential oil (OEO), carvacrol (Car), and thymol (Thy) was evaluated: OEO plus bioAgNP, Car plus bioAgNP, Thy plus bioAgNP, and Car plus Thy. This study shows that the mechanism of action of Thy, bioAgNP, and Thy plus bioAgNP involves damaging the membrane and cell wall (surface blebbing and disruption seen with an electron microscope), causing cytoplasmic molecule leakage (ATP, DNA, RNA, and total proteins) and oxidative stress by enhancing intracellular reactive oxygen species and lipid peroxidation; a similar mechanism happens for OEO and Car, except for oxidative stress. The combination containing bioAgNP and oregano derivatives, especially thymol, shows strategic antibacterial mechanism; thymol disturbs the selective permeability of the cell membrane and consequently facilitates access of the nanoparticles to bacterial cytoplasm. BioAgNP-treated Escherichia coli developed resistance to nanosilver after 12 days of daily exposition. The combination of Thy and bioAgNP prevented the emergence of resistance to both antimicrobials; therefore, mixture of antimicrobials is a strategy to extend their life. For antimicrobials alone, minimal bactericidal concentration ranges were 0.3-2.38 mg/ml (OEO), 0.31-1.22 mg/ml (Car), 0.25-1 mg/ml (Thy), and 15.75-31.5 μg/ml (bioAgNP). The time-kill assays showed that the oregano derivatives acted very fast (at least 10 s), while the bioAgNP took at least 30 min to kill Gram-negative bacteria and 7 h to kill methicillin-resistant Staphylococcus aureus (MRSA). All the combinations resulted in additive antibacterial effect, reducing significantly minimal inhibitory concentration and acting faster than the bioAgNP alone; they also showed no cytotoxicity. This study describes for the first time the effect of Car and Thy combined with bioAgNP (produced with F. oxysporum components) against bacteria for which efficient antimicrobials are urgently needed, such as carbapenem-resistant strains (E. coli, Klebsiella pneumoniae, Acinetobacter baumannii, and Pseudomonas aeruginosa) and MRSA.

Nanoparticles—Attractive Carriers of Antimicrobial Essential Oils

Microbial pathogens are the most prevalent cause of chronic infections and fatalities around the world. Antimicrobial agents including antibiotics have been frequently utilized in the treatment of infections due to their exceptional outcomes. However, their widespread use has resulted in the emergence of multidrug-resistant strains of bacteria, fungi, viruses, and parasites. Furthermore, due to inherent resistance to antimicrobial drugs and the host defence system, the advent of new infectious diseases, chronic infections, and the occurrence of biofilms pose a tougher challenge to the current treatment line. Essential oils (EOs) and their biologically and structurally diverse constituents provide a distinctive, inexhaustible, and novel source of antibacterial, antiviral, antifungal, and antiparasitic agents. However, due to their volatile nature, chemical susceptibility, and poor solubility, their development as antimicrobials is limited. Nanoparticles composed of biodegradable polymeric and inorganic materials have been studied extensively to overcome these limitations. Nanoparticles are being investigated as nanocarriers for antimicrobial delivery, antimicrobial coatings for food products, implantable devices, and medicinal materials in dressings and packaging materials due to their intrinsic capacity to overcome microbial resistance. Essential oil-loaded nanoparticles may offer the potential benefits of synergism in antimicrobial activity, high loading capacity, increased solubility, decreased volatility, chemical stability, and enhancement of the bioavailability and shelf life of EOs and their constituents. This review focuses on the potentiation of the antimicrobial activity of essential oils and their constituents in nanoparticulate delivery systems for a wide range of applications, such as food preservation, packaging, and alternative treatments for infectious diseases.

Antimicrobial and antibiofilm potentials of cinnamon oil and silver nanoparticles against Streptococcus agalactiae isolated from bovine mastitis: new avenues for countering resistance

BACKGROUND

Streptococcus agalactiae (S. agalactiae) is a contagious pathogen of bovine mastitis. It has financial implications for the dairy cattle industry in certain areas of the world. Since antimicrobial resistance increases in dairy farms, natural antimicrobials from herbal origins and nanoparticles have been given more attention as an alternative therapy. Hence, this study reported the antimicrobial and antibiofilm potentials of cinnamon oil, silver nanoparticles (AgNPs), and their combination against multidrug-resistant (MDR) S. agalactiae recovered from clinical bovine mastitis in Egypt.

RESULTS

Our findings revealed that 73% (146/200) of the examined milk samples collected from dairy cows with clinical mastitis were infected with Streptococci species. Of these, 9.59% (14/146) were identified as S. agalactiae and categorized as MDR. S. agalactiae isolates expressed four virulence genes (Hyl, cylE, scpB, and lmb) and demonstrated an ability to produce biofilms. Cinnamon oil showed high antimicrobial (MICs ≤0.063 μg /mL) and antibiofilm (MBIC50 = 4 μg/mL) potentials against planktonic and biofilms of S. agalactiae isolates, respectively. However, AgNPs showed reasonable antimicrobial (MICs ≤16 μg/mL) and relatively low antibiofilm (MBIC50 = 64 μg/mL) activities against screened isolates. Synergistic antimicrobial or additive antibiofilm interactions of cinnamon oil combined with AgNPs were reported for the first time. Scanning electron microscope (SEM) analysis revealed that biofilms of S. agalactiae isolates treated with cinnamon oil were more seriously damaged than observed in AgNPs cinnamon oil combination. Moreover, reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) showed that cinnamon oil exerted a remarkable down-regulation of pili biosynthesis genes (pilA and pilB) and their regulator (rogB) against S. agalactiae biofilms, meanwhile the AgNPs cinnamon oil combination demonstrated a lower efficacy.

CONCLUSIONS

This is an in vitro preliminary approach that documented the antibiofilm potential of cinnamon oil and the inhibitory activity of cinnamon oil and its combination with AgNPs against MDR S. agalactiae recovered from clinical mastitis. Further in vivo studies should be carried out in animal models to provide evidence of concept for implementing these alternative candidates in the treatment of dairy farms infected by streptococcal mastitis in the future.

Enteropathogenic Potential of Bacillus thuringiensis Isolates from Soil, Animals, Food and Biopesticides

Despite its benefits as biological insecticide, Bacillus thuringiensis bears enterotoxins, which can be responsible for a diarrhoeal type of food poisoning. Thus, all 24 isolates from foodstuffs, animals, soil and commercially used biopesticides tested in this study showed the genetic prerequisites necessary to provoke the disease. Moreover, though highly strain-specific, various isolates were able to germinate and also to actively move, which are further requirements for the onset of the disease. Most importantly, all isolates could grow under simulated intestinal conditions and produce significant amounts of enterotoxins. Cytotoxicity assays classified 14 isolates as highly, eight as medium and only two as low toxic. Additionally, growth inhibition by essential oils (EOs) was investigated as preventive measure against putatively enteropathogenic B. thuringiensis. Cinnamon Chinese cassia showed the highest antimicrobial activity, followed by citral, oregano and winter savory. In all tests, high strain-specific variations appeared and must be taken into account when evaluating the hazardous potential of B. thuringiensis and using EOs as antimicrobials. Altogether, the present study shows a non-negligible pathogenic potential of B. thuringiensis, independently from the origin of isolation. Generally, biopesticide strains were indistinguishable from other isolates. Thus, the use of these pesticides might indeed increase the risk for consumers’ health. Until complete information about the safety of the applied strains and formulations is available, consumers or manufacturers might benefit from the antimicrobial activity of EOs to reduce the level of contamination.

New Approach For Simvastatin As An Antibacterial: Synergistic Effect With Bio-Synthesized Silver Nanoparticles Against Multidrug-Resistant Bacteria

Background

Multidrug-resistant bacteria such as extended-spectrum beta-lactamase (ESBL), Enterobacteriaceae, and methicillin-resistant Staphylococcus aureus (MRSA) pose a challenge to the human health care system. MRSA is among the major causes of hospital-acquired and community infections.

Methods

Therefore, in the present study, we evaluated the antibacterial activity of silver nanoparticles synthesized by Fusarium oxysporum (AgNP_bio) in combination with simvastatin against reference and multidrug-resistant bacterial strains.

Results

Simvastatin showed a minimal inhibitory concentration (MIC) ranging from 0.062 to 0.25 mg mL⁻¹ against MRSA. AgNP_bio with a size of 77.68± 33.95 nm and zeta potential −34.6 ± 12.7 mV showed an MIC of 0.212 mg mL⁻¹ against S. aureus including MRSA strains. The checkerboard assay and time-kill curves exhibited a synergistic effect of the simvastatin-AgNP_bio combination on antibacterial activity against MRSA strains. The combination of simvastatin and AgNP_bio demonstrated antibacterial activity against Escherichia coli producing ESBL. Scanning electron microscopy showed the formation of cell surface protrusions after treatment with AgNP_bio and the formation of a large amorphous mass after treatment with simvastatin, both in MRSA.

Conclusion

Our results indicate that the combination of AgNP_bio and simvastatin could be a great future alternative in the control of bacterial infections, where, when combined with simvastatin, smaller doses of AgNP_bio are required, with the same antibacterial activity.

A review on anti-bacterials to combat resistance: From ancient era of plants and metals to present and future perspectives of green nano technological combinations

In the primitive era, humans benefited partially from plants and metals to treat microbial infections. Later these infections were cured with antibiotics but further suffered from resistance issues. In searching of an alternative, researchers developed an adjuvant therapy but were hampered by spreading resistance. Subsequently, nanoparticles (NPs) were proposed to cease the multi-drug resistant bacteria but were hindered due to toxicity issues. Recently, a novel adjuvant therapy employed metals and botanicals into innovative nanotechnology as nano-antibiotics. The combination of green synthesized metallic NPs with antibiotics seems to be a viable platform to combat against MDR bacteria by alleviating resistance and toxicity. This review focuses on the primitive to present era dealings with bacterial resistance mechanisms, newer innovations of nanotechnology and their multiple mechanisms to combat resistance. In addition, special focus is paid on greener NPs as antibiotic carriers, and their future prospects of controlled release and toxicity study.

A Novel Mathematical Model for Studying Antimicrobial Interactions Against Campylobacter jejuni

The aim of this study is to investigate the antimicrobial synergistic effect against Campylobacter jejuni, a leading foodborne pathogen that causes human gastroenteritis, by cinnamon oil, encapsulated curcumin, and zinc oxide nanoparticles (ZnO NPs). We compared three approaches to study the antimicrobial interactions, including the time-killing method, the fractional inhibitory concentration index (FICI) method, and a mathematical concentration-effect model. Isobologram analysis was performed to evaluate the synergy in different combinations, and a median-effect equation was applied to identify the combinations of synergistic effects at median, bacteriostatic, and bactericidal reduction levels. The time-killing method overestimated the synergistic interaction between antimicrobials, while the FICI method failed to detect an existing synergistic phenomenon. This lack of accuracy and sensitivity was mainly due to combining antimicrobials without a deep understanding of their concentration-effect relationships. Our results showed that each antimicrobial had a unique concentration-effect curve. Specifically, encapsulated curcumin showed a sharp sigmoidal curve unlike cinnamon oil and ZnO NPs. A mathematical model was applied to study the interaction between antimicrobials with a different shape of concentration-effect curve. We observed an additive effect of cinnamon oil/ZnO NPs and synergistic interactions of other binary combinations (cinnamon oil/encapsulated curcumin and ZnO NPs/encapsulated curcumin). The tertiary combination of cinnamon oil/ZnO NPs/encapsulated curcumin at IC₂₅ (additive line <1-log CFU/mL) presented the greatest synergistic effect by reducing the bacterial population over 8-log CFU/mL. This mathematical model provided an alternative strategy to develop a new antimicrobial strategy.

Antibacterial Activity of In Situ Prepared Chitosan/Silver Nanoparticles Solution Against Methicillin-Resistant Strains of Staphylococcus aureus

BACKGROUND

Investigation of new effective drugs against the methicillin-resistant strains of Staphylococcus aureus (MRSA) is an urgent issue of modern medicine. Antiseptics as an alternative of antibiotics are strong, sustained, and active preparations against resistant strains and do not violate microbiocenosis.

MATERIALS AND METHODS

The activity of in situ prepared chitosan-Ag nanoparticles (Ag NPs) solution with different component ratio was tested against MRSA isolated from patients. Ag NPs were synthesized via chemical reduction method using green chemistry approach. In order to improve antimicrobial activity and dispersibility of Ag NPs, surface modification of Ag NPs by cetrimonium bromide (CTAB) was performed. Ag NPs and chitosan-Ag NPs solution were characterized using X-ray diffraction, transmission electron microscopy, infrared spectroscopy, and spectrophotometric measurements.

RESULTS AND CONCLUSIONS

The results of XRD, FTIR, UV-Vis, and TEM measurements confirmed the chemical composition of chitosan and Ag NPs and their high purity. Chitosan-AgNPs solutions have shown their superior antimicrobial efficacy compared to its pure forms. At the same time, in situ preparation of chitosan-Ag NPs solution (chitosan powder 6.0 μg/ml, Ag/CTAB NPs) was not possible due to the precipitation of the components. This result is very promising and may be considered as an effective solution in fighting against drug-resistant bacteria.

Nanomaterials for alternative antibacterial therapy

Despite an array of cogent antibiotics, bacterial infections, notably those produced by nosocomial pathogens, still remain a leading factor of morbidity and mortality around the globe. They target the severely ill, hospitalized and immunocompromised patients with incapacitated immune system, who are prone to infections. The choice of antimicrobial therapy is largely empirical and not devoid of toxicity, hypersensitivity, teratogenicity and/or mutagenicity. The emergence of multidrug-resistant bacteria further intensifies the clinical predicament as it directly impacts public health due to diminished potency of current antibiotics. In addition, there is an escalating concern with respect to biofilm-associated infections that are refractory to the presently available antimicrobial armory, leaving almost no therapeutic option. Hence, there is a dire need to develop alternate antibacterial agents. The past decade has witnessed a substantial upsurge in the global use of nanomedicines as innovative tools for combating the high rates of antimicrobial resistance. Antibacterial activity of metal and metal oxide nanoparticles (NPs) has been extensively reported. The microbes are eliminated either by microbicidal effects of the NPs, such as release of free metal ions culminating in cell membrane damage, DNA interactions or free radical generation, or by microbiostatic effects coupled with killing potentiated by the host's immune system. This review encompasses the magnitude of multidrug resistance in nosocomial infections, bacterial evasion of the host immune system, mechanisms used by bacteria to develop drug resistance and the use of nanomaterials based on metals to overcome these challenges. The diverse annihilative effects of conventional and biogenic metal NPs for antibacterial activity are also discussed. The use of polymer-based nanomaterials and nanocomposites, alone or functionalized with ligands, antibodies or antibiotics, as alternative antimicrobial agents for treating severe bacterial infections is also discussed. Combinatorial therapy with metallic NPs, as adjunct to the existing antibiotics, may aid to restrain the mounting menace of bacterial resistance and nosocomial threat.

Antimicrobial Activity of Some Essential Oils-Present Status and Future Perspectives

Extensive documentation on the antimicrobial properties of essential oils and their constituents has been carried out by several workers. Although the mechanism of action of a few essential oil components has been elucidated in many pioneering works in the past, detailed knowledge of most of the compounds and their mechanism of action is still lacking. This knowledge is particularly important for the determination of the effect of essential oils on different microorganisms, how they work in combination with other antimicrobial compounds, and their interaction with food matrix components. Also, recent studies have demonstrated that nanoparticles (NPs) functionalized with essential oils have significant antimicrobial potential against multidrug- resistant pathogens due to an increase in chemical stability and solubility, decreased rapid evaporation and minimized degradation of active essential oil components. The application of encapsulated essential oils also supports their controlled and sustained release, which enhances their bioavailability and efficacy against multidrug-resistant pathogens. In the recent years, due to increasingly negative consumer perceptions of synthetic preservatives, interest in essential oils and their application in food preservation has been amplified. Moreover, the development of resistance to different antimicrobial agents by bacteria, fungi, viruses, parasites, etc. is a great challenge to the medical field for treating the infections caused by them, and hence, there is a pressing need to look for new and novel antimicrobials. To overcome these problems, nano-encapsulation of essential oils and exploiting the synergies between essential oils, constituents of essential oils, and antibiotics along with essential oils have been recommended as an answer to this problem. However, less is known about the interactions that lead to additive, synergistic, or antagonistic effects. A contributing role of this knowledge could be the design of new and more potent antimicrobial blends, and understanding of the interplay between the components of crude essential oils. This review is written with the purpose of giving an overview of current knowledge about the antimicrobial properties of essential oils and their mechanisms of action, components of essential oils, nano-encapsulated essential oils, and synergistic combinations of essential oils so as to find research areas that can facilitate applications of essential oils to overcome the problem of multidrug-resistant micro-organisms.

Ti-GO-Ag nanocomposite: the effect of content level on the antimicrobial activity and cytotoxicity

Surface modification of titanium (Ti) implants are extensively studied in order to obtain prominent biocompatibility and antimicrobial activity, especially preventing implant-associated infection. In this study, Ti substrates surface were modified by graphene oxide (GO) thin film and silver (Ag) nanoparticles via electroplating and ultraviolet reduction methods so as to achieve this purpose. Microstructures, distribution, quantities and spectral peaks of GO and Ag loading on the Ti sheets surface were characterized. GO-Ag-Ti multiphase nanocomposite exhibited excellent antimicrobial ability and anti-adherence performance. Subsequently, morphology, membrane integrity, apoptosis and relative genes expression of bacteria incubated on the Ti samples surface were monitored to reveal the bactericidal mechanism. Additionally, the cytotoxicity of Ti substrates incorporating GO thin film and Ag nanoparticles were investigated. GO-Ag-Ti composite configuration that have outstanding antibacterial properties will provide the foundation to study bone integration in vitro and in vivo in the future.

Core-shell magnetic nanoparticles display synergistic antibacterial effects against Pseudomonas aeruginosa and Staphylococcus aureus when combined with cathelicidin LL-37 or selected ceragenins

Core–shell magnetic nanoparticles (MNPs) are promising candidates in the development of new treatment methods against infections, including those caused by antibiotic-resistant pathogens. In this study, the bactericidal activity of human antibacterial peptide cathelicidin LL-37, synthetic ceragenins CSA-13 and CSA-131, and classical antibiotics vancomycin and colistin, against methicillin-resistant Staphylococcus aureus Xen 30 and Pseudomonas aeruginosa Xen 5, was assessed alone and in combination with core–shell MNPs. Fractional inhibitory concentration index and fractional bactericidal concentration index were determined by microdilution methods. The potential of combined therapy using nanomaterials and selected antibiotics was confirmed using chemiluminescence measurements. Additionally, the ability of tested agents to prevent bacterial biofilm formation was evaluated using crystal violet staining. In most conditions, synergistic or additive effects were observed when combinations of core–shell MNPs with ceragenins or classical antibiotics were used. Our study revealed that a mixture of membrane-active agents such as LL-37 peptide or ceragenin CSA-13 with MNPs potentialized their antibacterial properties and might be considered as a method of delaying and overcoming bacterial drug resistance.

Phytochemical profiling as a solution to palliate disinfectant limitations

The indiscriminate use of biocides for general disinfection has contributed to the increased incidence of antimicrobial tolerant microorganisms. This study aims to assess the potential of seven phytochemicals (tyrosol, caffeic acid, ferulic acid, cinnamaldehyde, coumaric acid, cinnamic acid and eugenol) in the control of planktonic and sessile cells of Staphylococcus aureus and Escherichia coli. Cinnamaldehyde and eugenol showed antimicrobial properties, minimum inhibitory concentrations of 3-5 and 5-12 mM and minimum bactericidal concentrations of 10-12 and 10-14 mM against S. aureus and E. coli, respectively. Cinnamic acid was able to completely control adhered bacteria with effects comparable to peracetic acid and sodium hypochlorite and it was more effective than hydrogen peroxide (all at 10 mM). This phytochemical caused significant changes in bacterial membrane hydrophilicity. The observed effectiveness of phytochemicals makes them interesting alternatives and/or complementary products to commonly used biocidal products. Cinnamic acid is of particular interest for the control of sessile cells.

Green synthesis and antibacterial effects of aqueous colloidal solutions of silver nanoparticles using camomile terpenoids as a combined reducing and capping agent

Green synthesis method using camomile extract was applied to synthesize silver nanoparticles to tune their antibacterial properties merging the synergistic effect of camomile and Ag. Scanning transmission electron microscopy revealed that camomile extract (CE) consisted of porous globular nanometer sized structures, which were a perfect support for Ag nanoparticles. The Ag nanoparticles synthesized with the camomile extract (AgNPs/CE) of 7 nm average sizes, were uniformly distributed on the CE support, contrary to the pure Ag nanoparticles synthesized with glucose (AgNPs/G), which were over 50 nm in diameter and strongly agglomerated. The energy dispersive X-ray spectroscopy chemical analysis showed that camomile terpenoids act as a capping and reducing agent being adsorbed on the surface of AgNPs/CE enabling their reduction from Ag(+) and preventing them from agglomeration. Fourier transform infrared and ultraviolet-visible spectroscopy measurements confirmed these findings, as the spectra of AgNPs/CE, compared to pure CE, did not contain the 1109 cm(-1) band, corresponding to -C-O groups of terpenoids and the peaks at 280 and 320 nm, respectively. Antibacterial tests using four bacteria strains showed that the AgNPs/CE performed five times better compared to CE AgNPs/G samples, reducing totally all the bacteria in 2 h.

Synergistic and Additive Effect of Oregano Essential Oil and Biological Silver Nanoparticles against Multidrug-Resistant Bacterial Strains

Bacterial resistance to conventional antibiotics has become a clinical and public health problem, making therapeutic decisions more challenging. Plant compounds and nanodrugs have been proposed as potential antimicrobial alternatives. Studies have shown that oregano (Origanum vulgare) essential oil (OEO) and silver nanoparticles have potent antibacterial activity, also against multidrug-resistant strains; however, the strong organoleptic characteristics of OEO and the development of resistance to these metal nanoparticles can limit their use. This study evaluated the antibacterial effect of a two-drug combination of biologically synthesized silver nanoparticles (bio-AgNP), produced by Fusarium oxysporum, and OEO against Gram-positive and Gram-negative bacteria, including multidrug-resistant strains. OEO and bio-AgNP showed bactericidal effects against all 17 strains tested, with minimal inhibitory concentrations (MIC) ranging from 0.298 to 1.193 mg/mL and 62.5 to 250 μM, respectively. Time-kill curves indicated that OEO acted rapidly (within 10 min), while the metallic nanoparticles took 4 h to kill Gram-negative bacteria and 24 h to kill Gram-positive bacteria. The combination of the two compounds resulted in a synergistic or additive effect, reducing their MIC values and reducing the time of action compared to bio-AgNP used alone, i.e., 20 min for Gram-negative bacteria and 7 h for Gram-positive bacteria. Scanning electron microscopy (SEM) revealed similar morphological alterations in Staphylococcus aureus (non-methicillin-resistant S. aureus, non-MRSA) cells exposed to three different treatments (OEO, bio-AgNP and combination of the two), which appeared cell surface blebbing. Individual and combined treatments showed reduction in cell density and decrease in exopolysaccharide matrix compared to untreated bacterial cells. It indicated that this composition have an antimicrobial activity against S. aureus by disrupting cells. Both compounds showed very low hemolytic activity, especially at MIC levels. This study describes for the first time the synergistic and additive interaction between OEO and bio-AgNP produced by F. oxysporum against multidrug-resistant bacteria, such as MRSA, and β-lactamase- and carbapenemase-producing Escherichia coli and Acinetobacter baumannii strains. These results indicated that this combination can be an alternative in the control of infections with few or no treatment options.

Effect of Eugenol against Streptococcus agalactiae and Synergistic Interaction with Biologically Produced Silver Nanoparticles

Streptococcus agalactiae (group B streptococci (GBS)) is an important infections agent in newborns associated with maternal vaginal colonization. Intrapartum antibiotic prophylaxis in GBS-colonized pregnant women has led to a significant reduction in the incidence of early neonatal infection in various geographic regions. However, this strategy may lead to resistance selecting among GBS, indicating the need for new alternatives to prevent bacterial transmission and even to treat GBS infections. This study reported for the first time the effect of eugenol on GBS isolated from colonized women, alone and in combination with silver nanoparticles produced by Fusarium oxysporum (AgNPbio). Eugenol showed a bactericidal effect against planktonic cells of all GBS strains, and this effect appeared to be time-dependent as judged by the time-kill curves and viability analysis. Combination of eugenol with AgNPbio resulted in a strong synergistic activity, significantly reducing the minimum inhibitory concentration values of both compounds. Scanning and transmission electron microscopy revealed fragmented cells and changes in bacterial morphology after incubation with eugenol. In addition, eugenol inhibited the viability of sessile cells during biofilm formation and in mature biofilms. These results indicate the potential of eugenol as an alternative for controlling GBS infections.

Facile biofunctionalization of silver nanoparticles for enhanced antibacterial properties, endotoxin removal, and biofilm control

Infectious diseases cause a huge burden on healthcare systems worldwide. Pathogenic bacteria establish infection by developing antibiotic resistance and modulating the host’s immune system, whereas opportunistic pathogens like Pseudomonas aeruginosa adapt to adverse conditions owing to their ability to form biofilms. In the present study, silver nanoparticles were biofunctionalized with polymyxin B, an antibacterial peptide using a facile method. The biofunctionalized nanoparticles (polymyxin B-capped silver nanoparticles, PBSNPs) were assessed for antibacterial activity against multiple drug-resistant clinical strain Vibrio fluvialis and nosocomial pathogen P. aeruginosa. The results of antibacterial assay revealed that PBSNPs had an approximately 3-fold higher effect than the citrate-capped nanoparticles (CSNPs). Morphological damage to the cell membrane was followed by scanning electron microscopy, testifying PBSNPs to be more potent in controlling the bacterial growth as compared with CSNPs. The bactericidal effect of PBSNPs was further confirmed by Live/Dead staining assays. Apart from the antibacterial activity, the biofunctionalized nanoparticles were found to resist biofilm formation. Electroplating of PBSNPs onto stainless steel surgical blades retained the antibacterial activity against P. aeruginosa. Further, the affinity of polymyxin for endotoxin was exploited for its removal using PBSNPs. It was found that the prepared nanoparticles removed 97% of the endotoxin from the solution. Such multifarious uses of metal nanoparticles are an attractive means of enhancing the potency of antimicrobial agents to control infections.

Comparative study of antimicrobial activity of AgBr and Ag nanoparticles (NPs)

The diverse mechanism of antimicrobial activity of Ag and AgBr nanoparticles against gram-positive and gram-negative bacteria and also against several strains of candida was explored in this study. The AgBr nanoparticles (NPs) were prepared by simple precipitation of silver nitrate by potassium bromide in the presence of stabilizing polymers. The used polymers (PEG, PVP, PVA, and HEC) influence significantly the size of the prepared AgBr NPs dependently on the mode of interaction of polymer with Ag⁺ ions. Small NPs (diameter of about 60–70 nm) were formed in the presence of the polymer with low interaction as are PEG and HEC, the polymers which interact with Ag⁺ strongly produce nearly two times bigger NPs (120–130 nm). The prepared AgBr NPs were transformed to Ag NPs by the reduction using NaBH₄. The sizes of the produced Ag NPs followed the same trends – the smallest NPs were produced in the presence of PEG and HEC polymers. Prepared AgBr and Ag NPs dispersions were tested for their biological activity. The obtained results of antimicrobial activity of AgBr and Ag NPs are discussed in terms of possible mechanism of the action of these NPs against tested microbial strains. The AgBr NPs are more effective against gram-negative bacteria and tested yeast strains while Ag NPs show the best antibacterial action against gram-positive bacteria strains.

Comparative Study on the Synergistic Action of Differentially Synthesized Silver Nanoparticles with β-Cephem Antibiotics and Chloramphenicol

Synergistic activity of cephem antibiotics with silver nanoparticles (Ag NPs) was investigated. Silver nanoparticles were synthesized through biological and chemical method. The combined action of β-lactam cephem antibiotics with both green and chemically synthesized silver nanoparticles enhances the antibacterial activity against wide range of antibiotic resistant pathogens and making them applicable to medical devices and microbial control systems. Synergistic activity of chloramphenicol with silver nanoparticles was also studied.