Tannic Acid-Stabilized Silver Nanoparticles Used in Biomedical Application as an Effective Antimelioidosis and Prolonged Efflux Pump Inhibitor against Melioidosis Causative Pathogen.

Burkholderia pseudomallei is the causative pathogen of melioidosis and this bacterium is resistant to several antibiotics. Silver nanoparticles (AgNPs) are an interesting agent to develop to solve this bacterial resistance. Here, we characterize and assess the antimelioidosis activity of AgNPs against these pathogenic bacteria. AgNPs were characterized and displayed a maximum absorption band at 420 nm with a spherical shape, being well-monodispersed and having high stability in solution. The average size of AgNPs is 7.99 ± 1.46 nm. The antibacterial efficacy of AgNPs was evaluated by broth microdilution. The bactericidal effect of AgNPs was further assessed by time-kill kinetics assay. Moreover, the effect of AgNPs on the inhibition of the established biofilm was investigated by the crystal violet method. In parallel, a study of the resistance induction development of B. pseudomallei towards AgNPs with efflux pump inhibiting effect was performed. We first found that AgNPs had strong antibacterial activity against both susceptible and ceftazidime-resistant (CAZ-resistant) strains, as well as being efficiently active against B. pseudomallei CAZ-resistant strains with a fast-killing mode via a bactericidal effect within 30 min. These AgNPs did not only kill planktonic bacteria in broth conditions, but also in established biofilm. Our findings first documented that the resistance development was not induced in B. pseudomallei toward AgNPs in the 30th passage. We found that AgNPs still showed an effective efflux pump inhibiting effect against these bacteria after prolonged exposure to AgNPs at sublethal concentrations. Thus, AgNPs have valuable properties for being a potent antimicrobial agent to solve the antibiotic resistance problem in pathogens.

Effect of acyl chain length on therapeutic activity and mode of action of the CX-KYR-NH2 antimicrobial lipopeptide.

Peptide lipidation has proven to be an inexpensive and effective strategy for designing next-generation peptide-based drug compounds. In this study, the effect of the acyl chain length of ultrashort LiPs (CX-KYR-NH2; X=10, 12, 14 and 16) on their bacterial killing and membrane disruption kinetics was investigated. The geometric mean of the minimum inhibitory concentration (MIC) values for 4 pathogenic bacterial strains was 25 µM, with a selectivity index of 10.24 for C14-KYR-NH2. LiPs at all concentrations exhibited no cytotoxicity towards human erythrocytes, but towards Vero cells at 80 µM. All the LiPs adopted secondary structure in a membrane mimicking environment. C14-KYR-NH2 aggregated above 256 µM, while C16-KYR-NH2 did above 80 µM. All LiPs showed outer membrane permeabilization within 3 min after treatment, yet the extent and kinetics of inner membrane penetration and depolarization were dependent on the acyl chain length. Cell death subsequently occurred within 10 min, and killing activity appeared to correlate most with depolarization activity but not with outer or inner membrane permeability. AFM imaging of cells treated with C14-KYR-NH2 revealed rupture of the cell surface and cytosolic leakage depending on the length of incubation. This study highlights and follows the progression of events that occur during the membrane disintegration process over time, and determines the optimal amphipathicity of ultrashort LiPs with 12-14 carbon atoms for this membrane disrupting activity. The fast acting bactericidal properties of ultrashort LiPs with optimal chain lengths make them promising candidates for drug lead compounds.

Integrated remediation and detoxification of triclocarban-contaminated water using waste-derived biochar-immobilized cells by long-term column experiments.

Triclocarban (TCC), an antibacterial agent commonly used in personal care products, is one of the top ten contaminants of emerging concern in various environmental media, including soil and contaminated water in vadose zone. This study aimed to investigate TCC-contaminated water remediation using biochar-immobilized bacterial cells. Pseudomonas fluorescens strain MC46 (MC46), an efficient TCC-degrading isolate, was chosen, whereas agro-industrial carbonized waste as biochar was directly used as a sustainable cell immobilization carrier. According to the long-term TCC removal performance results (160 d), the biochar-immobilized cells consistently exhibited high TCC removal efficiencies (84-97%), whereas the free MC46 removed TCC for 76-94%. At 100 days, the detachment of the MC46 cells from the immobilized cell column was observed. The micro-Fourier-transform infrared spectroscopy results indicated that extracellular polymeric substance (EPS) was produced, but polysaccharide and protein fractions were washed out of the column. The lipid fraction of EPS adhered to the biochar, promoting TCC sorption for long-term treatment. The shortening of MC46 cells improved the tolerance of TCC toxicity. The TCC-contaminated water was successfully detoxified by the biochar-immobilized MC46 cells. Overall, the waste-derived biochar-immobilized cell system proposed in this study for the removal of emerging contaminants, including TCC, is efficient, economical, and aligned with the sustainable development concept of value-added utilization of waste.

Investigation of Radiation Effect on Structural and Optical Properties of GaAs under High-Energy Electron Irradiation.

A systematic investigation of the changes in structural and optical properties of a semi-insulating GaAs (001) wafer under high-energy electron irradiation is presented in this study. GaAs wafers were exposed to high-energy electron beams under different energies of 10, 15, and 20 MeV for absorbed doses ranging from 0-2.0 MGy. The study showed high-energy electron bombardments caused roughening on the surface of the irradiated GaAs samples. At the maximum delivered energy of 20 MeV electrons, the observed root mean square (RMS) roughness increased from 5.993 (0.0 MGy) to 14.944 nm (2.0 MGy). The increased RMS roughness with radiation doses was consistent with an increased hole size of incident electrons on the GaAs surface from 0.015 (0.5 MGy) to 0.066 nm (2.0 MGy) at 20 MeV electrons. Interestingly, roughness on the surface of irradiated GaAs samples affected an increase in material wettability. The study also observed the changes in bandgap energy of GaAs samples after irradiation with 10, 15, and 20 MeV electrons. The band gap energy was found in the 1.364 to 1.397 eV range, and the observed intense UV-VIS spectra were higher than in non-irradiated samples. The results revealed an increase of light absorption in irradiated GaAs samples to be higher than in original-based samples.

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.

AFM Study of Nanoscale Membrane Perturbation Induced by Antimicrobial Lipopeptide C14 KYR.

Lipopeptides have been extensively studied as potential antimicrobial agents. In this study, we focused on the C14-KYR lipopeptide, a modified version of the KYR tripeptide with myristic acid at the N-terminus. Here, membrane perturbation of live E. coli treated with the parent KYR and C14-KYR peptides was compared at the nanoscale level using AFM imaging. AFM analyses, including average cellular roughness and force spectroscopy, revealed the severe surface disruption mechanism of C14-KYR. A loss of surface roughness and changes in topographic features included membrane shrinkage, periplasmic membrane separation from the cell wall, and cytosolic leakage. Additional evidence from synchrotron radiation FTIR microspectroscopy (SR-FTIR) revealed a marked structural change in the membrane component after lipopeptide attack. The average roughness of the E. coli cell before and after treatment with C14-KYR was 129.2 ± 51.4 and 223.5 ± 14.1 nm, respectively. The average rupture force of the cell treated with C14-KYR was 0.16 nN, four times higher than that of the untreated cell. Our study demonstrates that the mechanistic effect of the lipopeptide against bacterial cells can be quantified through surface imaging and adhesion force using AFM.

Antimicrobial action of the cyclic peptide bactenecin on Burkholderia pseudomallei correlates with efficient membrane permeabilization.

Burkholderia pseudomallei is a category B agent that causes Melioidosis, an acute and chronic disease with septicemia. The current treatment regimen is a heavy dose of antibiotics such as ceftazidime (CAZ); however, the risk of a relapse is possible. Peptide antibiotics are an alternative to classical antibiotics as they exhibit rapid action and are less likely to result in the development of resistance. The aim of this study was to determine the bactericidal activity against B. pseudomallei and examine the membrane disrupting abilities of the potent antimicrobial peptides: bactenecin, RTA3, BMAP-18 and CA-MA. All peptides exhibited >97% bactericidal activity at 20 µM, with bactenecin having slightly higher activity. Long term time-kill assays revealed a complete inhibition of cell growth at 50 µM bactenecin and CA-MA. All peptides inhibited biofilm formation comparable to CAZ, but exhibited faster kinetics (within 1 h). Bactenecin exhibited stronger binding to LPS and induced perturbation of the inner membrane of live cells. Interaction of bactenecin with model membranes resulted in changes in membrane fluidity and permeability, leading to leakage of dye across the membrane at levels two-fold greater than that of other peptides. Modeling of peptide binding on the membrane showed stable and deep insertion of bactenecin into the membrane (up to 9 Å). We propose that bactenecin is able to form dimers or large ß-sheet structures in a concentration dependent manner and subsequently rapidly permeabilize the membrane, leading to cytosolic leakage and cell death in a shorter period of time compared to CAZ. Bactenecin might be considered as a potent antimicrobial agent for use against B. pseudomallei.