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

BRAVI, VIVIANA S.; SILVERO C., MARÍA JAZMÍN; BECERRA, MARÍA CECILIA

Rosario

Congreso; 7ma Reunión Internacional; 2023

Universidad Nacional de Rosario

The disinfectants that are currently on the market do not guarantee the complete removal orelimination 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 thehospital setting. For this reason, it was proposed to develop a suspension from an aqueous plantextract with antimicrobial activity and the ability to generate silver nanoparticles in situ, which couldhave greater disinfectant power compared with commercial disinfectants. The aerial parts ofMinthostachys mollis, an endemic species of the province of Córdoba (Argentina), were collectedduring 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 maceratedin a shaker between 25-27°C, with distilled water for 7 hours. Next, the reductive capacity of theplant extract was evaluated using the Folin-Ciocalteu reagent and tannic acid as a standard. In situsynthesis of the nanoparticles was performed using 50 uL of aqueous plant extract and 150 uL of 10mM 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 ATCC29213 and Escherichia coli ATCC 25922 (104 CFU/mL) by counting of CFU/mL on Tryptic Soy agar. Tofurther study the mechanism of action, Transmission Electron Microscopy was performed toevaluate the alterations of the ultrastructure. Absorption maxima were observed at 430 nm in thesynthesis with the aqueous extract (pH= 6.58), which indicates the formation of AgNP@Mm withthe presence of different geometric shapes, prevailing the spherical one, with an averagenanoparticle size of 20 nm and 77 nm, as measured by SEM and DLS, respectively. Regarding theantimicrobial activity, it was possible to verify that the silver nanoparticles with the aqueous extractof Minthostachys mollis have the capacity to inhibit the growth of S. aureus and E. coli after 7 and 5min at room temperature, respectively. AgNO3 and NP Citrate (silver nanoparticles reduced withsodium citrate) were used as positive controls. The aqueous extract of Minthostachys mollis did notinhibit the bacterial growth. The disintegration of the cocci (S. aureus) membrane was visualizedwith 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 corroboratedthat 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 shorttimes of action.