This research aims to provide an alternative eco-friendly way to obtain silver species and assess their bactericidal activity. This study reports the synthesis of Ag₂O nanoparticles and Ag nanoparticles reduced with a green synthesis method, using a low-cost and commercial Aloe vera extract. The crystalline phases of Ag and Ag₂O nanoparticles were analyzed by X-ray diffraction. The oxidation states for both species were determined by X-ray photoelectron spectroscopy. The optical properties of the material were studied through optical absorption, which resulted in well-defined band centered at 545 nm. This result is attributed to the morphology and size of the silver nanoparticles. In addition, antibacterial tests were performed on AgNPs biosynthesized with A. vera with the Kirby–Bauer protocol on Gram-negative and Gram-positive bacteria Escherichia coli and Staphylococcus aureaus, respectively. Moreover, antifungal tests were performed with various species from Candida.

The problem of water pollution by persistent substances and microorganisms requires solutions that materials such as silver-modified titanium dioxide can provide due to their excellent photocatalytic and antimicrobial properties. However, the synthesis methods conventionally used to obtain these materials involve toxic chemical reagents such as sodium borohydride (NaBH₄). The search for alternative synthesis methods that use environmentally friendly substances, such as the biosynthesis method, was evaluated. Silver-titanium dioxide (Ag-TiO₂) was synthesized by a Eucalyptus globulus L. extract as a reductive agent through sol-gel and microwave-assisted sol-gel processes. Four different solvents were tested to extract secondary metabolites to determine their roles in reducing silver nanoparticles. Titanium dioxide nanoparticles with sizes from 11 to 14 nm were obtained in the anatase phase, and no narrowing of the bandgap was observed (3.1–3.2 eV) for the Ag-TiO₂ materials compared with the pure TiO₂. Interestingly, the bacterial inhibition values were close to 100%, suggesting an effective antimicrobial mechanism related to the properties of silver. Finally, by the physicochemical characterization of the materials and their antimicrobial properties, it was possible to obtain a suitable biosynthesized Ag-TiO₂ material as a green option for water disinfection that may be compared to the conventional methods.

Trichoderma atroviride responds to various environmental stressors through the mitogen-activated protein kinase (MAPK) Tmk3 and MAPK-kinase Pbs2 signaling pathways. In fungi, orthologues to Tmk3 are regulated by a histidine kinase (HK) sensor. However, the role of T. atroviride HKs remains unknown. In this regard, the function of the T. atroviride HK Nik1 was analyzed in response to stressors regulated by Tmk3. The growth of the Δnik1 mutant strains was compromised under hyperosmotic stress; mycelia were less resistant to lysing enzymes than the WT strain, while conidia of Δnik1 were more sensitive to Congo red; however, ∆pbs2 and ∆tmk3 strains showed a more drastic defect in cell wall stability. Light-regulated blu1 and grg2 gene expression was induced upon an osmotic shock through Pbs2-Tmk3 but was independent of Nik1. The encoding chitin synthases chs1 and chs2 genes were downregulated after an osmotic shock in the WT, but chs1 and chs3 expression were enhanced in ∆nik1, ∆pbs2, and ∆tmk3. The vegetative growth and conidiation by light decreased in ∆nik1, although Nik1 was unrequired to activate the light-responsive genes by Tmk3. Altogether, Nik1 regulates responses related to the Pbs2-Tmk3 pathway and suggests the participation of additional HKs to respond to stress.

Anti-microbial peptides play a vital role in the defense mechanisms of various organisms performing functions that range from the elimination of microorganisms, through diverse mechanisms, to the modulation of the immune response, providing protection to the host. Among these peptides, cathelicidins, a well-studied family of anti-microbial peptides, are found in various animal species, including reptiles. Due to the rise in anti-microbial resistance, these compounds have been suggested as potential candidates for developing new drugs. In this study, we identified and characterized a cathelicidin-like peptide called Aquiluscidin (Aq-CATH) from transcripts obtained from the skin and oral mucosa of the Querétaro’s dark rattlesnake, Crotalus aquilus. The cDNA was cloned, sequenced, and yielded a 566-base-pair sequence. Using bioinformatics, we predicted that the peptide precursor contains a signal peptide, a 101-amino-acid conserved cathelin domain, an anionic region, and a 34-amino-acid mature peptide in the C-terminal region. Aq-CATH and a derived 23-amino-acid peptide (Vcn-23) were synthesized, and their anti-microbial activity was evaluated against various species of bacteria in in vitro assays. The minimal inhibitory concentrations against bacteria ranged from 2 to 8 μg/mL for both peptides. Furthermore, at concentrations of up to 50 μM, they exhibited no significant hemolytic activity (<2.3% and 65% cell viability at 25 µM). Finally, this study represents the first identification of an antimicrobial peptide in Crotalus aquilus, which belongs to the cathelicidin family and exhibits the characteristic features of these peptides. Both Aq-CATH and its derived molecule, Vcn-23, displayed remarkable inhibitory activity against all tested bacteria, highlighting their potential as promising candidates for further antimicrobial research.

Background: The need to combat and reduce the incidence, virulence, and drug resistance of species belonging to Candida genus, has led to the development of new strategies. Nanotechnology, through the implementation of nanomaterials, has emerged as an infallible tool to treat various diseases caused by pathogens, where its mechanisms of action prevent the development of undesirable pharmacological resistance. Objective: The antifungal activity and adjuvant properties of biogenic silver nanoparticles in different Candida species (C. parapsilosis, C. glabrata, and C. albicans) are evaluated. Methods: The biogenic metallic nanoparticles were developed by quercetin-mediated biological synthesis. The physicochemical properties were studied by light scattering, electrophoretic mobility, UV-vis and infrared spectroscopy, and transmission electron microscopy. The elucidation of mechanisms of antifungal action was carried out under stress conditions in Candida species at the cell wall and response to oxidative stress. Results: Small silver nanoparticles (≈ 16.18 nm) with irregular morphology, and negative surface electrical charge (≈ -48.99 mV), were obtained through quercetin-mediated biosynthesis. Infrared spectra showed that the surface of silver nanoparticles is functionalized with the quercetin molecule. The antifungal activity of biogenic nanoparticles had efficacy in the following trend C. glabrata ≥ C. parapsilosis > C. albicans. Biogenic nanoparticles and stressors showed synergistic and potentiated antifungal effects through cell damage, osmotic stress, cell wall damage, and oxidative stress. Conclusion: Silver nanoparticles synthesized by quercetin-mediated biosynthesis could be implemented as a powerful adjuvant agent to enhance the inhibition effects of diverse compounds over different Candida species.