Search

Microbial technology offers a green alternative for the synthesis of value-added nanomaterials. In particular, fungal compounds can improve silver nanoparticle production, stabilizing colloidal nanoparticles. Based on a previous study by our group, silver nanoparticles obtained using the extracellular cell-free extracts of Phanerochaete chrysosporium (PchNPs) have shown antimicrobial and antibiofilm activity against Gram-negative bacteria. Moreover, nisin—a bacteriocin widely used as a natural food preservative—has recently gained much attention due its antimicrobial action against Gram-positive bacteria in biomedical applications. Therefore, the aim of this work was to conjugate biogenic silver nanoparticles (PchNPs) with nisin to obtain nanoconjugates (PchNPs@nis) with enhanced antimicrobial properties. Characterization assays were conducted to determine physicochemical properties of PchNPs@nis, and also their antibacterial and antibiofilm activities were studied. The formation of PchNPs@nis was confirmed by UV-Vis, TEM, and Raman spectroscopy analysis. Different PchNPs@nis nanobioconjugates showed diameter values in the range of 60–130 nm by DLS and surface charge values between −20 and −13 mV. Nisin showed an excellent affinity to PchNPs, with binding efficiencies higher than 75%. Stable synthesized PchNPs@nis nanobioconjugates were not only able to inhibit biofilm formation by S. aureus, but also showed inhibition of the planktonic cell growth of Staphyloccocus aureus and Escherichia coli, broadening the spectrum of action of the unconjugated antimicrobials against Gram-positive and Gram-negative bacteria. In conclusion, these results show the promising application of PchNPs@nis, prepared via green technology, as potential antimicrobial nanomaterials.

Antimicrobial resistance is a growing concern in public health and current research shows an important role for bacterial biofilms in recurrent or chronic infections. New strategies, therefore, are necessary to overcome antimicrobial resistance, through the development of new therapies that could alter or inhibit biofilm formation. In this sense, antibiofilm natural products are very promising. In this work, a bioprospection of antimicrobial and antibiofilm extracts from Uruguayan soil bacteria and insect gut bacteria was carried out. Extracts from extracellular broths were tested for their ability to inhibit planktonic cell growth and biofilm formation. Genomic analysis of Bacillus cereus ILBB55 was carried out. All extracts were able to inhibit the growth of, at least, one microorganism and several extracts showed MICs lower than 500 µg mL−1 against microorganisms of clinical relevance (Staphylococcus aureus, Pseudomonas aeruginosa, and Enterobacter cloacae). Among the extracts evaluated for biofilm inhibition only ILBB55, from B. cereus, was able to inhibit, S. aureus (99%) and P. aeruginosa (62%) biofilms. Genomic analysis of this strain showed gene clusters similar to other clusters that code for known antimicrobial compounds. Our study revealed that extracts from soil bacteria and insect gut bacteria, especially from B. cereus ILBB55, could be potential candidates for drug discovery to treat infectious diseases and inhibit S. aureus and P. aeruginosa biofilms.

Microorganisms offer an alternative green and scalable technology for the synthesis of value added products. Fungi secrete high quantities of bioactive substances, which play dual-functional roles as both reducing and stabilizing agents in the synthesis of colloidal metal nanoparticles such as silver nanoparticles, which display potent antimicrobial properties that can be harnessed for a number of industrial applications. The aim of this work was the production of silver nanoparticles using the extracellular cell free extracts of Phanerochaete chrysosporium, and to evaluate their activity as antimicrobial and antibiofilm agents. The 45–nm diameter silver nanoparticles synthesized using this methodology possessed a high negative surface charge close to −30 mV and showed colloidal stability from pH 3–9 and under conditions of high ionic strength ([NaCl] = 10–500 mM). A combination of environmental SEM, TEM, and confocal Raman microscopy was used to study the nanoparticle-E. coli interactions to gain a first insight into their antimicrobial mechanisms. Raman data demonstrate a significant decrease in the fatty acid content of E. coli cells, which suggests a loss of the cell membrane integrity after exposure to the PchNPs, which is also commensurate with ESEM and TEM images. Additionally, these biogenic PchNPs displayed biofilm disruption activity for the eradication of E. coli and C. albicans biofilms.

Species of the genus Senecio have been traditionally employed with medical purposes and it has been demonstrated that some of them have anti-proliferative activity on cancer-derived cell lines. In South America S. madagascariensis is one of the most important representatives of the genus. Almost all species contain pyrrolizidine alkaloids (PA), substances that can lead to hepatic damage. Thus, the aim of this work was to determine the cytotoxic activity of a low PAs extract of S. madagascariensis on a cancer-derived cell line. A chloroform extract from plant material was produced and it was demonstrated to have a PAs concentration lower than 200 µg/g (w/w). Two stock solutions were made with DMSO and acetone as solvents and were diluted in culture medium (DMEM). Cells from urinary bladder transitional cell carcinoma T24 were cultured in 96 well plates (10⁴ cells/well) and incubated for 24 hours with dilutions of the extracts at the following concentrations, 0.5 mg/mL, 0.25 mg/mL, 0.125 mg/mL and 0.06 mg/mL. Cell viability was evaluated by the MTT colorimetric technique. Both solutions of S. madagascariensis extracts (acetone and DMSO) showed cytotoxic activity. In both cases, the degree of cytotoxicity was dependent on the concentration of the solution.