Silver nanoparticles as a new generation of antimicrobials

Silver has been in use since time immemorial in the form of metallic silver, silver nitrate, silver sulfadiazine for the treatment of burns, wounds and several bacterial infections. But due to the emergence of several antibiotics the use of these silver compounds has been declined remarkably. Nanotechnology is gaining tremendous impetus in the present century due to its capability of modulating metals into their nanosize, which drastically changes the chemical, physical and optical properties of metals. Metallic silver in the form of silver nanoparticles has made a remarkable comeback as a potential antimicrobial agent. The use of silver nanoparticles is also important, as several pathogenic bacteria have developed resistance against various antibiotics. Hence, silver nanoparticles have emerged up with diverse medical applications ranging from silver based dressings, silver coated medicinal devices, such as nanogels, nanolotions, etc.     

柱[5]芳烃衍生物对细菌抗菌活性及生物被膜抑制的研究进展北大核心

病原体的耐药性很强,其生物被膜(biofilm,BF)的形成是导致耐药性的主要原因之一。生物被膜一旦形成,根除难度很大,会导致患者持久性感染,引发多种慢性疾病,并给全球医疗体系带来沉重负担。柱芳烃(pillararenes)是一类具有独特柱状结构的新型大环化合物,由于其在构建功能化和生物活性材料开发中的潜在应用引起人们广泛的关注。此外,它们在预防和控制抗生素耐药性(antimicrobial resistance,AMR)方面具有广阔的应用前景。本文综述了柱[5]芳烃衍生物对细菌病原菌的抗菌活性,并进一步揭示其在抗菌活性中的抑菌机制,尤其是对生物被膜的抑制作用。在此基础上,探索新的抑菌杀菌策略,用非传统药物以解决抗生素耐药性问题,以期为开发新的抗菌剂防控生物被膜或治疗细菌感染提供理论依据。     

Antibacterial potential of hGlyrichin encoded by a human gene

Emerging multidrug‐resistant (MDR) bacteria are an enormous threat to human life because of their resistance to currently available antibiotics. The genes encoding antibacterial peptides have been studied extensively and are excellent candidates for a new generation of antibiotic drugs to fight MDR bacteria. In contrast to traditional antibiotics, antibacterial peptides, which do not cause drug resistance, have an unparalleled advantage. However, because most antibacterial peptides originate in species other than humans, the hetero‐immunological rejection of antibacterial peptides is a key disadvantage that limits their clinical application. In this study, we identify hGlyrichin as a potential human antibacterial polypeptide. The hGlyrichin polypeptide kills a variety of bacteria including the MDR bacteria methicillin‐resistant Staphylococcus aureus, MDR Pseudomonas aeruginosa, and MDR tubercle bacillus. A 19 amino acid peptide (pCM19) at positions 42–60 of hGlyrichin is crucial for its antibacterial activity. The hGlyrichin polypeptide kills bacteria through the destruction of the bacterial membrane. In addition, all peptides that are homologous to hGlyrichin have antibacterial activity and can penetrate the bacterial membrane. Importantly, hGlyrichin does not cause hemolytic side effects in vitro or in vivo. Therefore, based on the virtues of hGlyrichin, i.e., the absence of hetero‐immunological rejection and hemolytic side effects and the unambiguous efficacy of killing pathogenic MDR bacteria, we propose hGlyrichin as a potential human antibacterial polypeptide. Copyright © 2011 European Peptide Society and John Wiley & Sons, Ltd.     

Bactericidal effect of silver nanoparticles against multidrug-resistant bacteria

Infections caused by drug-resistant microorganisms result in significant increases in mortality, morbidity, and cost related to prolonged treatments. The antibacterial activity of silver nanoparticles against some drug-resistant bacteria has been established, but further investigation is needed to determine whether these particles could be an option for the treatment and prevention of drug-resistant microbial infections. Hence, we challenged different drug-resistant pathogens of clinical importance (multidrug-resistant Pseudomonas aeruginosa, ampicillin-resistant Escherichia coli O157:H7 and erythromycin-resistant Streptococcus pyogenes) with a suspension of silver nanoparticles. By means of a luciferase-based assay, it was determined that silver nanoparticles (1) inactivate a panel of drug-resistant and drug-susceptible bacteria (Gram positive and Gram negative), (2) exert their antibacterial activity through a bactericidal rather than bacteriostatic mechanism, and (3) inhibit the bacterial growth rate from the time of first contact between the bacteria and the nanoparticles. Additionally, strains with a resistant phenotype to silver nanoparticle were developed and used to explore the bactericidal mode of action of silver nanoparticles. Through a Kirby–Bauer test, it was shown that silver nanoparticles’ general mechanism of bactericidal action is based on inhibition of cell wall synthesis, protein synthesis mediated by the 30s ribosomal subunit, and nucleic acid synthesis. Our data suggest that silver nanoparticles are effective broad-spectrum biocides against a variety of drug-resistant bacteria, which makes them a potential candidate for use in pharmaceutical products and medical devices that may help to prevent the transmission of drug-resistant pathogens in different clinical environments.     

Mycosynthesis and characterization of silver nanoparticles and their activity against some human pathogenic bacteria

The aim of this study was to biosynthesis silver nanoparticles from the fungus Nigrospora sphaerica isolated from soil samples and to examine their activity against five human pathogenic strains of bacteria viz. Escherichia coli, Proteus mirabilis, Pseudomonas aeruginosa, Salmonella typhi and Staphylococcus aureus using disc diffusion method. The synergistic effect of silver nanoparticles in combination with commonly used antibiotic Gentamycin against the selected bacteria was also examined. The synthesized silver nanoparticles from free-cell filtrate were characterized by using UV–Vis spectrophotometer analysis, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM). UV–Vis spectrophotometer analysis showed a peak at 420 nm indicating the synthesis of silver nanoparticles, FTIR analysis verified the detection of protein capping of silver nanoparticles while SEM micrographs revealed that the silver nanoparticles are dispersed and aggregated and mostly having spherical shape within the size range between 20 and 70 nm. The synthesized silver nanoparticles exhibited a varied growth inhibition activity (15–26 mm diam inhibition zones) against the tested pathogenic bacteria. A remarkable increase of bacterial growth inhibition (26–34 mm diam) was detected when a combination of silver nanoparticles and Gentamycin was used. A significant increase in fold area of antibacterial activity was observed when AgNPs in combination with Gentamycin was applied. The synthesized silver nanoparticles produced by the fungus N. sphaerica is a promising to be used as safe drug in medical therapy due to their broad spectrum against pathogenic bacteria.     

Plants as a Source of Bacterial Resistance Modulators and Anti-Infective Agents

The spread of multidrug-resistant (MDR) strains of bacteria necessitates the discovery of new classes of antibacterials and compounds that inhibit these resistance mechanisms. At present, there are no single chemical entity plant-derived antibacterials used clinically, and this chemically diverse group deserves consideration as a source for two major reasons. First, plants have exceptional ability to produce cytotoxic agents and second there is an ecological rationale that antimicrobial natural products should be present or synthesised de novo in plants following microbial attack to protect the producer from pathogenic microbes in its environment. We have been characterising plant-derived products that are either antibacterial in their own right, or modulators of resistance in bacterial strains possessing multidrug efflux mechanisms. These efflux transporters are responsible for resistance to certain antibiotics and antiseptics and occur in strains of methicillin-resistant Staphylococcus aureus (MRSA), a major clinical problem at present. We are also investigating plant sources for compounds with activity against mycobacteria with a view to discovering drug leads with potential activity toward tuberculosis (TB) producing species. This paper will briefly review the literature on plant derived bacterial resistance modifying agents and antibacterials. Examples in this area from our own work will be given. The activities of plant-derived antibacterials show that there are many potential new classes of antibacterial agents which should undergo further cytotoxicity, microbial specificity and preclinical studies.     

Nanoparticles functionalized with ampicillin destroy multiple-antibiotic-resistant isolates of Pseudomonas aeruginosa and Enterobacter aerogenes and methicillin-resistant Staphylococcus aureus

We show here that silver nanoparticles (AgNP) were intrinsically antibacterial, whereas gold nanoparticles (AuNP) were antimicrobial only when ampicillin was bound to their surfaces. Both AuNP and AgNP functionalized with ampicillin were effective broad-spectrum bactericides against Gram-negative and Gram-positive bacteria. Most importantly, when AuNP and AgNP were functionalized with ampicillin they became potent bactericidal agents with unique properties that subverted antibiotic resistance mechanisms of multiple-drug-resistant bacteria.     

Comparative Proteomic Profiling of Methicillin‐Susceptible and Resistant Staphylococcus aureus

Staphylococcus aureus is a highly successful human pathogen responsible for a wide range of infections. This study provides insights into the virulence, pathogenicity, and antimicrobial resistance determinants of methicillin‐susceptible and methicillin‐resistant S. aureus (MSSA; MRSA) recovered from non‐healthcare environments. Three environmental MSSA and three environmental MRSA are selected for proteomic profiling using isobaric tag for relative and absolute quantitation tandem mass spectrometry (iTRAQ MS/MS). Gene Ontology annotation and Kyoto Encyclopedia of Genes and Genomes pathway annotation are applied to interpret the functions of the proteins detected. 792 proteins are identified in MSSA and MRSA. Comparative analysis of MRSA and MSSA reveals that 8 of out 792 proteins are upregulated and 156 are downregulated. Proteins that have differences in abundance are predominantly involved in catalytic and binding activity. Among 164 differently abundant proteins, 29 are involved in pathogenesis, antimicrobial resistance, stress response, mismatch repair, and cell wall synthesis. Twenty‐two proteins associated with pathogenicity including SPA, SBI, CLFA, and DLT are upregulated in MRSA. Moreover, the upregulated pathogenic protein ENTC2 in MSSA is determined to be a super antigen, potentially capable of triggering toxic shock syndrome in the host. Enhanced pathogenicity, antimicrobial resistance, and stress response are observed in MRSA compared to MSSA.     

A novel cysteine‐free venom peptide with strong antimicrobial activity against antibiotics‐resistant pathogens from the scorpion Opistophthalmus glabrifrons

Antibiotic‐resistant bacteria, such as methicillin‐resistant Staphylococcus aureus and vancomycin‐resistant Enterococcus, pose serious threat to human health. The outbreak of antibiotic‐resistant pathogens in recent years emphasizes once again the urgent need for the development of new antimicrobial agents. Here, we discovered a novel antimicrobial peptide from the scorpion Opistophthalmus glabrifrons, which was referred to as Opisin. Opisin consists of 19 amino acid residues without disulfide bridges. It is a cationic, amphipathic, and α‐helical molecule. Protein sequence homology search revealed that Opisin shares 42.1–5.3% sequence identities to the 17/18‐mer antimicrobial peptides from scorpions. Antimicrobial assay showed that Opisin is able to potently inhibit the growth of the tested Gram‐positive bacteria with the minimal inhibitory concentration (MIC) values of 4.0–10.0 μM; in contrast, it possesses much lower activity against the tested Gram‐negative bacteria and a fungus. It is interesting to see that Opisin is able to strongly inhibit the growth of methicillin‐ and vancomycin‐resistant pathogens with the MICs ranging from 2.0 to 4.0 μM and from 4.0 to 6.0 μM, respectively. We found that at a concentration of 5 × MIC, Opisin completely killed all the cultured methicillin‐resistant Staphylococcus aureus. These results suggest that Opisin is a promising therapeutic candidate for the treatment of the antibiotic‐resistant bacterial infections. Copyright © 2015 European Peptide Society and John Wiley & Sons, Ltd.     

Nanoparticles combined with cefixime as an effective synergistic strategy against Salmonella enterica typhi

Enteric fever caused by Salmonella typhi has been the most crucial health issue in rural people, especially in Southeast Asia and Africa. Another disease, Salmonellosis, caused by a large group of bacteria of the genus Salmonella, cause substantial economic loss resulting from mortality and morbidity. Higher concentration and repeated use of antibiotics to treat these diseases will likely develop antibiotic resistance among the microbes. The nanoparticle has good penetration power and can kill microbes. Combining two strategies by using nanoparticles with antibiotics kills microbes and reduces the chances of the development of antibiotics resistance. Silver, Nickel, Copper, and Zinc oxide Nanoparticles were chemically synthesized and characterized in this study. Silver nanoparticles at a concentration of 10 µg/ml inhibit all the strains under study.In comparison, silver nanoparticles (16.90 µg/ml), Nickel nanoparticles (83 µg ml^?1), Copper nanoparticles (249 µg ml^?1), and Zinc oxide (1614 µg ml^?1) along with 50 µg/ml cefixime gave maximum zone of inhibition of 35 mm, 19 mm, 31 mm and 23 mm respectively. The antimicrobial assay showed that silver nanoparticles presented good antibacterial performance against all multi-drug-resistant pathogenic Salmonella sp alone as well as in combinations. The present study proved that silver nanoparticles at the lowest concentration along with cefixime could be a possible alternative to control the multi-drug-resistant pathogens.     

Design,Synthesis, Antibacterial Evaluation and Molecular Docking Studies of Some Newer Baenzothiazole Containing Aryl and Alkaryl Hydrazides

The alarming rise of bacterial resistance is occurring worldwide and endangering the efficacy of antibiotics. Therefore, development of new and efficient antibacterial agents remains paramount. In the present work, we designed and synthesized a series of N′-(1,3-benzothiazol-2-yl)-substituted aryl/aralkyl hydrazides C1 – C27 and evaluated them in vitro for their antibacterial activity. Among all tested compounds, C10 , C15 , and C24 showed potent activity against Staphylococcus aureus ATCC 43300 (MRSA). Minimum bactericidal concentration studies of synthesized compounds are performed against selected bacterial strains. Time kill kinetics showed that the compounds C10 and C15 possess bactericidal activity against MRSA ATCC 43300, while compound C24 possess bactericidal activity against S. aureus NCIM 5022. In the extra-precision docking, compounds C1 – C27 exhibited interactions mainly with the N-terminal and central domains of S. aureus GyrB catalytic pocket. Binding free energy (ΔG_bind) of compounds C1 – C27 /3U2K complexes were computed by MM-GBSA approach. Free energy components indicated Coulomb energy term as favorable for binding, while van der Waals and electrostatic solvation energy terms strongly disfavored the binding. ADMET properties of synthesized compounds C1 – C27 are also computed.     

Antimicrobial resistance of bacteria isolated from slaughtered and retail chickens in South Africa

Animal feed is increasingly being supplemented with antibiotics to decrease the risk of epidemics in animal husbandry. This practice could lead to the selection for antibiotic resistant micro-organisms. The aim of this study was to determine the level of antibiotic resistant bacteria present on retail and abattoir chicken. Staphylococci, Enterobacteriaceae, Salmonella and isolates from total aerobic plate count were tested for resistance to vancomycin, streptomycin, methicillin, tetracycline and gentamicin using the disc diffusion susceptibility test; resistance to penicillin was determined using oxacillin. Results from the antibiotic code profile indicated that many of the bacterial strains were displaying multiple antibiotic resistance (MAR). A larger proportion of resistance to most antibiotics, except for vancomycin, was displayed by the abattoir samples, therefore suggesting that the incidence of MAR pathogenic bacteria was also higher in the abattoir samples. This resistance spectrum of abattoir samples is a result of farmers adding low doses of antibiotics to livestock feed to improve feeding efficiency so that the animals need less food to reach marketable weight. The lower incidence of MAR pathogenic bacteria in the retail samples is a result of resistance genes being lost due to lack of selective pressure, or to the fact that the resistant flora are being replaced by more sensitive flora during processing. The use of subtherapeutic levels of antibiotics for prophylaxis and as growth promoters remains a concern as the laws of evolution dictate that microbes will eventually develop resistance to practically any antibiotic. Selective pressure exerted by widespread antimicrobial use is therefore the driving force in the development of antibiotic resistance. This study indicated that a large proportion of the bacterial flora on fresh chicken is resistant to a variety of antibiotics, and that resultant food-related infections will be more difficult to treat.     

Sesquiterpenoids with Anti‐MDR Staphylococcus aureus Activities from Ferula ferulioides

Seven new sesquiterpenoids together with 21 known sesquiterpenoid derivatives were isolated from the medicinal plant Ferula ferulioides (Steud .) Korovin . Their structures were elucidated by comprehensive spectroscopic analyses and chemical transformations. The isolated compounds were evaluated for their antibacterial activities against a panel of bacteria including multidrug‐resistant (MDR) and methicillin‐resistant Staphylococcus aureus (MRSA), displaying minimum inhibitory concentration (MIC) values in the range of 0.5–128 mg/l.     

Marine Sediment Bacteria Harbor Antibiotic Resistance Genes Highly Similar to Those Found in Human Pathogens

The ocean is a natural habitat for antibiotic-producing bacteria, and marine aquaculture introduces antibiotics into the ocean to treat infections and improve aquaculture production. Studies have shown that the ocean is an important reservoir of antibiotic resistance genes. However, there is a lack of understanding and knowledge about the clinical importance of the ocean resistome. We investigated the relationship between the ocean bacterial resistome and pathogenic resistome. We applied high-throughput sequencing and metagenomic analyses to explore the resistance genes in bacterial plasmids from marine sediments. Numerous putative resistance determinants were detected among the resistance genes in the sediment bacteria. We also found that several contigs shared high identity with transposons or plasmids from human pathogens, indicating that the sediment bacteria recently contributed or acquired resistance genes from pathogens. Marine sediment bacteria could play an important role in the global exchange of antibiotic resistance.     

Gram‐positive bacteria produce membrane vesicles: Proteomics‐based characterization of Staphylococcus aureus‐derived membrane vesicles

Although archaea, Gram‐negative bacteria, and mammalian cells constitutively secrete membrane vesicles (MVs) as a mechanism for cell‐free intercellular communication, this cellular process has been overlooked in Gram‐positive bacteria. Here, we found for the first time that Gram‐positive bacteria naturally produce MVs into the extracellular milieu. Further characterizations showed that the density and size of Staphylococcus aureus‐derived MVs are both similar to those of Gram‐negative bacteria. With a proteomics approach, we identified with high confidence a total of 90 protein components of S. aureus‐derived MVs. In the group of identified proteins, the highly enriched extracellular proteins suggested that a specific sorting mechanism for vesicular proteins exists. We also identified proteins that facilitate the transfer of proteins to other bacteria, as well to eliminate competing organisms, antibiotic resistance, pathological functions in systemic infections, and MV biogenesis. Taken together, these observations suggest that the secretion of MVs is an evolutionally conserved, universal process that occurs from simple organisms to complex multicellular organisms. This information will help us not only to elucidate the biogenesis and functions of MVs, but also to develop therapeutic tools for vaccines, diagnosis, and antibiotics effective against pathogenic strains of Gram‐positive bacteria.     

Do we need new antibiotics? The search for new targets and new compounds

Resistance to antibiotics and other antimicrobial compounds continues to increase. There are several possibilities for protection against pathogenic microorganisms, for instance, preparation of new vaccines against resistant bacterial strains, use of specific bacteriophages, and searching for new antibiotics. The antibiotic search includes: (1) looking for new antibiotics from nontraditional or less traditional sources, (2) sequencing microbial genomes with the aim of finding genes specifying biosynthesis of antibiotics, (3) analyzing DNA from the environment (metagenomics), (4) reexamining forgotten natural compounds and products of their transformations, and (5) investigating new antibiotic targets in pathogenic bacteria.     

Antimicrobial activities and membrane‐active mechanism of CPF‐C1 against multidrug‐resistant bacteria,a novel antimicrobial peptide derived from skin secretions of the tetraploid frog Xenopus clivii

Hospital‐acquired infections caused by multidrug‐resistant bacteria pose significant challenges for treatment, which necessitate the development of new antibiotics. Antimicrobial peptides are considered potential alternatives to conventional antibiotics. The skin of Anurans (frogs and toads) amphibians is an extraordinarily rich source of antimicrobial peptides. CPF‐C1 is a typical cationic antimicrobial peptide that was originally isolated from the tetraploid frog Xenopus clivii. Our results showed that CPF‐C1 has potent antimicrobial activity against both sensitive and multidrug‐resistant bacteria. It disrupted the outer and inner membranes of bacterial cells. CPF‐C1 induced both propidium iodide uptake into the bacterial cell and the leakage of calcein from large liposome vesicles, which suggests a mode of action that involves membrane disturbance. Scanning electron microscopy and transmission electron microscopy verified the morphologic changes of CPF‐C1‐treated bacterial cells and large liposome vesicles. The membrane‐dependent mode of action signifies that the CPF‐C1 peptide functions freely and without regard to conventional resistant mechanisms. Additionally, it is difficult for bacteria to develop resistance against CPF‐C1 under this action mode. Other studies indicated that CPF‐C1 had low cytotoxicity against mammalian cell. In conclusion, considering the increase in multidrug‐resistant bacterial infections, CPF‐C1 may offer a new strategy that can be considered a potential therapeutic agent for the treatment of diseases caused by multidrug‐resistant bacteria. Copyright © 2014 European Peptide Society and John Wiley & Sons, Ltd.     

Multicellular organization in bacteria as a target for drug therapy

Antibiotic treatments are now reaching the limit of their efficiency, especially in hospitals where certain bacteria are resistant to all available drugs. The development of new drugs against which resistance would be slower to evolve is an important challenge. Recent advances have shown that a potential strategy is to target global properties of infections instead of harming each individual bacterium. Consider an analogy with multicellular organisms. In order to kill an animal two strategies are possible. One can kill each of its cells individually. This is what antibiotics do to get rid of bacterial infections. An alternate way, for instance, is to disorganize the hormonal system of animal's body, leading eventually to its death. This second strategy could also be employed against infections, in place of antibiotics. Bacteria are indeed often involved into coordinated activities within a group, and certain drugs are able to disorganize these activities by blocking bacterial communication. In other words, these drugs are able to target infections as a whole, rather than individuals within infections. The present paper aims at analysing the consequence of this peculiarity on the evolution of bacterial resistance. We use a mathematical model, based on branching process, to calculate the fixation probability of a mutant resistant to this type of drug, and finally to predict the speed of resistance evolution. We show that this evolution is several orders of magnitude slower than in the case of antibiotic resistance. The explanation is as follows. By targeting treatments against adaptive properties of groups instead of individuals, we shift one level up the relevant unit of organization generating resistance. Instead of facing billions of bacteria with a very rapid evolutionary rate, these alternate treatments face a reduced number of larger organisms with lower evolutionary potential. In conclusion, this result leads us to emphasize the strong potential of anti‐bacterial treatments aiming at disorganizing social traits of microbes rather than at killing every individual.