Recent studies with silver nanoparticles (AgNPs) and the history of silver metal as a broad-spectrum bactericidal and virucidal agent, places silver as one of the future biocidal candidates in the field of nanomedicine to eliminate bacteria and viruses, especially multidrug resistant ones. In this review, we have described the various morphologies of AgNPs and correlated the enhanced bactericidal activity with their prominent {111} facets. In addition to prioritizing the characterization we have also discussed the importance of quantifying AgNPs and silver ion content (Ag+) and their different mechanisms at the chemical, biological, pharmacological, and toxicological levels. The mechanism of action of AgNPs against various bacteria and viruses including the SARS-CoV-2 was analyzed in order to understand its effectiveness as an antimicrobial agent with therapeutic efficacy and low toxicity. Further, there is the need to characterize AgNPs and quantify the content of free Ag+ for the implementation of new systematic studies of this promising agent in nanomedicine and in clinical practice.

Introduction: The incidence of severe fungal infections has increased worldwide and poses a serious global threat, especially among immunocompromised (HIV+, newly transplanted) and critically ill patients. Emergence of multidrug-resistant species also contributes to a growing mortality rate associated to fungal infections, which demands new drugs or new therapeutic strategies to manage these conditions. The use of metal ions, their nanoparticles or complexes with other binders are a promising therapeutic alternative, since it was recently demonstrated that silver nanoparticles (AgNP) possess potential antimicrobial effects in a wide range of microorganisms (bacteria, fungi and virus). Combination of amphotericin-B (AmB), a standard antifungal associated to important clinical side effects and toxicity, to AgNP could be a new promising therapeutic strategy against fungal infections. Objective: To assess the combined in vitro effects between silver nanoparticles and subinhibitory concentrations of AmB on pathogenic fungi. Methodology: The silver nanoparticles (AgNP) were electrochemically synthetized (18V and 500 mA), using polished silver plates in distilled water during 30 minutes at 90 o C, and thereafter characterized and quantified by ultraviolet-visible spectroscopy and inductively coupled plasmaatomic emission spectrometry, respectively. Pathogenic fungal species, Criptococcus neoformans (serotype A clinical isolate H99) and Candida albicans (ATCC 90028), were grown in vitro in the presence of serial dilutions of AgNP alone or AgNP in combination with sub-inhibitory concentration of AmB (siAmB; 0.1µg/mL) during 48 hours, for assessment of fungal growth inhibition. Evaluation of yeast fungal growth was realized spectrophotometrically (592 nm). All statistical analyses were performed using one-way ANOVA followed by Newman-Keuls test. Statistics with a value of p<0.05 were considered significant. Results: The concentration of electrochemically generated AgNP resulted in 18 ppm and showed no presence of silver ions in solution. AgNP alone (0.007-18 ppm) significantly impaired in vitro C. neoformans growth after 48 hours in all concentrations analyzed (p<0.05). Association of serial dilutions of AgNP and siAmB (0.1µg/mL) significantly potencialized impairment of C. neoformans growth, when compared to AgNP alone (p<001). In contrast, AgNP alone only inhibited C. albicans at 0.45, 0.9 and 18 ppm (p<0.05). Interestingly AgNP and siAmB in vitro association impaired C. albicans growth in all AgNP concentrations utilized (p<0.001). Control group using AmB (1µg/mL) completely blocked C. neoformans and C. albicans growth while siAmB (0.1µg/mL) only impaired C. neoformans and C. albicans growth (65 and 73%, respectively) after 48 h. Conclusion: AgNP acted as an enhancing agent, potentializing the inhibitory growth effects of AmB on pathogenic fungi. Novel antifungal therapeutic strategies using AgNP, isolated or in combination, should be considered in the future.

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