Microbiological study of a suspension with silver nanoparticles and aqueous extract of Minthostachys mollis Griseb.

BRAVI V; SILVERO C MJ; BECERRA M. C

Rosario

Congreso; VII reunion RICIFA; 2023

Univ. Nac. de Rosario y UNC

The disinfectants that are currently on the market do not guarantee the complete removal or elimination of bacteria and/or biofilms in the different products for medical use (endoscopes, probes, respirators, etc.) and surfaces. This is partly due to microbial resistance, especially in the hospital setting. For this reason, it was proposed to develop a suspension from an aqueous plant extract with antimicrobial activity and the ability to generate silver nanoparticles in situ, which could have greater disinfectant power compared with commercial disinfectants. The aerial parts of Minthostachys mollis, an endemic species of the province of Córdoba (Argentina), were collected during the flowering and/or fruiting season, and dried in the shade at room temperature. Subsequently, extracts were made from the crushed leaves reduced to a fine powder and macerated in a shaker between 25-27°C, with distilled water for 7 hours. Next, the reductive capacity of the plant extract was evaluated using the Folin-Ciocalteu reagent and tannic acid as a standard. In situ synthesis of the nanoparticles was performed using 50 uL of aqueous plant extract and 150 uL of 10 mM AgNO3 at 85°C. AgNP@Mm were characterized by UV spectrophotometry, DLS and SEM-EDS. The antimicrobial capacity of the nanoparticles was evaluated on Staphylococcus aureus ATCC 29213 and Escherichia coli ATCC 25922 (104 CFU/mL) by counting of CFU/mL on Tryptic Soy agar. To further study the mechanism of action, Transmission Electron Microscopy was performed to evaluate the alterations of the ultrastructure. Absorption maxima were observed at 430 nm in the synthesis with the aqueous extract (pH= 6.58), which indicates the formation of AgNP@Mm with the presence of different geometric shapes, prevailing the spherical one, with an average nanoparticle size of 20 nm and 77 nm, as measured by SEM and DLS, respectively. Regarding the antimicrobial activity, it was possible to verify that the silver nanoparticles with the aqueous extract of Minthostachys mollis have the capacity to inhibit the growth of S. aureus and E. coli after 7 and 5 min at room temperature, respectively. AgNO3 and NP Citrate (silver nanoparticles reduced with sodium citrate) were used as positive controls. The aqueous extract of Minthostachys mollis did not inhibit the bacterial growth. The disintegration of the cocci (S. aureus) membrane was visualized with the entry of the nanoparticles and the “blebbing” effect. On the other hand, “bubbling” phenomenon and lysis occurred in the bacilli (E. coli) membrane. Stability studies have corroborated that there were no modifications in the size of the nanoparticles in the two-month follow-up period. We consider that AgNP@Mm have the potential to be used as a disinfectant thanks to their short times of action.