The ability of microorganisms to generate resistance outcompetes with the generation of new and efficient antibiotics; therefore, it is critical to develop novel antibiotic agents and treatments to control bacterial infections. An alternative to this worldwide problem is the use of nanomaterials with antimicrobial properties. Silver nanoparticles (AgNPs) have been extensively studied due to their antimicrobial effect in different organisms. In this work, the synergistic antimicrobial effect of AgNPs and conventional antibiotics was assessed in Gram-positive and Gram-negative bacteria. AgNPs minimal inhibitory concentration was 10–12 μg mL-1 in all bacterial strains tested, regardless of their different susceptibility against antibiotics. Interestingly, a synergistic antimicrobial effect was observed when combining AgNPs and kanamycin according to the fractional inhibitory concentration index, FICI: <0.5), an additive effect by combining AgNPs and chloramphenicol (FICI: 0.5 to 1), whereas no effect was found with AgNPs and β-lactam antibiotics combinations. Flow cytometry and TEM analysis showed that sublethal concentrations of AgNPs (6–7 μg mL-1) altered the bacterial membrane potential and caused ultrastructural damage, increasing the cell membrane permeability. No chemical interactions between AgNPs and antibiotics were detected. We propose an experimental supported mechanism of action by which combinatorial effect of antimicrobials drives synergy depending on their specific target, facilitated by membrane alterations generated by AgNPs. Our results provide a deeper understanding about the synergistic mechanism of AgNPs and antibiotics, aiming to combat antimicrobial infections efficiently, especially those by multi-drug resistant microorganisms, in order to mitigate the current crisis due to antibiotic resistance.

Candida albicans is the most common fungal pathogen in humans, and recently some studies have reported the antifungal activity of silver nanoparticles (AgNPs) against some Candida species. However, ultrastructural analyses on the interaction of AgNPs with these microorganisms have not been reported. In this work we evaluated the effect of AgNPs on C. albicans, and the minimum inhibitory concentration (MIC) was found to have a fungicidal effect. The IC50 was also determined, and the use of AgNPs with fluconazole (FLC), a fungistatic drug, reduced cell proliferation. In order to understand how AgNPs interact with living cells, the ultrastructural distribution of AgNPs in this fungus was determined. Transmission electron microscopy (TEM) analysis revealed a high accumulation of AgNPs outside the cells but also smaller nanoparticles (NPs) localized throughout the cytoplasm. Energy dispersive spectroscopy (EDS) analysis confirmed the presence of intracellular silver. From our results it is assumed that AgNPs used in this study do not penetrate the cell, but instead release silver ions that infiltrate into the cell leading to the formation of NPs through reduction by organic compounds present in the cell wall and cytoplasm.

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The current emerging COVID-19 pandemic has caused a global impact on every major aspect of our societies. It is known that SARS-Cov-2 can endure harsh environmental conditions for up to 72 h, which may contribute to its rapid spread. Therefore, effective containment strategies, such as sanitizing, are critical. Nanotechnology can represent an alternative to reduce the COVID-19 spread, particularly in critical areas, such as healthcare facilities and public places. Nanotechnology-based products are effective at inhibiting different pathogens, including viruses, regardless of their drug-resistant profile, biological structure, or physiology. Although there are several approved nanotechnology-based antiviral products, this work aims to highlight the use of nanomaterials as sanitizers for the prevention of the spread of mainly SARS-Cov-2. It has been widely demonstrated that nanomaterials are an alternative for sanitizing surfaces to inactivate the virus. Also, antimicrobial nanomaterials can reduce the risk of secondary microbial infections on COVID-19 patients, as they inhibit the bacteria and fungi that can contaminate healthcare-related facilities. Finally, cost-effective, easy-to-synthesize antiviral nanomaterials could reduce the burden of the COVID-19 on challenging environments and in developing countries.

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Experimental Section S3-S13 1 H and 13 C NMR spectra S13-S20 Fluorescence lifetime decay spectra and data S21 Femtosecond-picosecond transient absorption spectra S22 Nanosecond transient absorption spectra S23 ROS detection studies S24 Concentration of polymers/oligomer used for the antifungal studies in μg/mL S25 Antifungal studies S26-S29 SEM images of treated and untreated C. albicans biofilm S29 10 Cytotoxicity and β-glucan interaction Studies S30 11 References S31 S3 I. Experimental section Materials All starting materials and reagents were obtained from commercial sources (Sigma-Aldrich, Fisher Scientific) and used without further purification. Glutaraldehyde and Osmium tetroxide were obtained from Ted Pella. Solvents were dried by standard methods or by elution through a MBraun solvent purification system. 2.5% glutaraldehyde and 1% Osmium tetroxide solutions were prepared in filtered MilliQ water at the moment of the sample preparation. All reactions were performed under a nitrogen atmosphere, unless stated otherwise. Thin-layer chromatography (TLC) was conducted with TLC Silica gel plastic plates and visualized with UVGL-15 compact lamps (254/365 nm). Flash chromatography was performed using Teledyne automated flash chromatography system using RediSep Rf normal-phase silica flash columns (60 Å; particle size 35-70 μm (230 x 400 mesh)). Characterization methods 1 H NMR and 13 C NMR spectra were recorded in CDCl3, DMSO-d6 and D2O using a 300 or 500 MHz spectrometer (with TMS as an internal standard). Chemical shifts were reported in parts per million (ppm, δ) using the solvent as the internal standard. The coupling constants are reported in hertz (Hz). Splitting patterns are designated as s (singlet), bs (broad singlet), d (doublet), t (triplet), and m (multiplet). UV-Visible spectra were recorded using the Shimadzu UV-2600 spectrophotometer. Corrected steady-state fluorescence spectra were obtained with an Edinburgh fluorometer. A 1 cm 2 square pyrex cuvette was used for solution spectra, and emission

By comparing Candida albicans virulence and the mucosal bacterial composition in a mouse oral infection model, we were able to dissect the effects of the host environment (immunosuppression), infection with C. albicans , and local modulating factors (availability of sucrose as a carbon source) on the mucosal bacterial microbiome and its role on fungal virulence. We showed that changes in endogenous microbial communities in response to sucrose can lead to attenuation of fungal disease.

Candida auris is an emergent multidrug-resistant pathogenic yeast with an unprecedented ability for a fungal organism to easily spread between patients in clinical settings, leading to major outbreaks in healthcare facilities. The formation of biofilms by C. auris contributes to infection and its environmental persistence. Most antifungals and sanitizing procedures are not effective against C. auris, but antimicrobial nanomaterials could represent a viable alternative to combat the infections caused by this emerging pathogen. We have previously described an easy and inexpensive method to synthesize silver nanoparticles (AgNPs) in non-specialized laboratories. Here, we have assessed the antimicrobial activity of the resulting AgNPs on C. auris planktonic and biofilm growth phases. AgNPs displayed a strong antimicrobial activity against all the stages of all C. auris strains tested, representative of four different clades. Under planktonic conditions, minimal inhibitory concentration (MIC) values of AgNPs against the different strains were <0.5 μg ml −1 ; whereas calculated IC 50 values for inhibition of biofilms formation were <2 μg ml −1 for all, but one of the C. auris strains tested. AgNPs were also active against preformed biofilms formed by all different C. auris strains, with IC 50 values ranging from 1.2 to 6.2 μg ml −1. Overall, our results indicate potent activity of AgNPs against strains of C. auris, both under planktonic and biofilm growing conditions, and indicate that AgNPs may contribute to the control of infections caused by this emerging nosocomial threat.