The Primary Mode of Action of Lippia graveolens Essential Oil on Salmonella enterica subsp. Enterica Serovar Typhimurium.

Essential oils are known to exhibit diverse antimicrobial properties, showing their value as a natural resource. Our work aimed to investigate the primary mode of action of Cuban Lippia graveolens (Kunth) essential oil (EO) against Salmonella enterica subsp. enterica serovar Typhimurium (S. enterica ser. Typhimurium). We assessed cell integrity through various assays, including time-kill bacteriolysis, loss of cell material with absorption at 260 and 280 nm, total protein leakage, and transmission electron microscopy (TEM). The impact of L. graveolens EO on membrane depolarization was monitored and levels of intracellular and extracellular ATP were measured by fluorescence intensity. The minimum inhibitory and bactericidal concentrations (MIC and MBC) of L. graveolens EO were 0.4 and 0.8 mg/mL, respectively. This EO exhibited notable bactericidal effects on treated cells within 15 min without lysis or leakage of cellular material. TEM showed distinct alterations in cellular ultrastructure, including membrane shrinkage and cytoplasmic content redistribution. We also observed disruption of the membrane potential along with reduced intracellular and extracellular ATP concentrations. These findings show that L. graveolens EO induces the death of S. enterica ser. Typhimurium, important information that can be used to combat this foodborne disease-causing agent.

Biosynthesis of fluorescent silver nanoparticles from Leea coccinea leaves and their antibacterial potentialities against Xanthomonas phaseoli pv phaseoli.

The synthesis of silver nanoparticles (SNP) from plants is a simple, fast and environmentally safe route. In the present study, the aqueous extract of fresh leaves from Leea coccinea L. was evaluated as a possible source of reducing and stabilizing agents to obtain SNP. The synthesized SNP were characterized by spectroscopic techniques such as UV-visible spectrophotometry and Fourier transform infrared spectroscopy (FTIR), scanning electron and confocal microscopies and the antimicrobial activity against Xanthomonas phaseoli pv. phaseoli was evaluated using agar diffusion methods. The results showed that the evaluated extract was promising for the green synthesis of the SNP, which was visually identified by the formation of a dark-brown complex and the presence of a peak of maximum absorption at 470 nm in a UV-VIS spectrum. FTIR spectrum of SNP showed main characteristic signals of aromatic compounds, carboxylic group among others confirmed by phytochemical screening that made evident the presence of flavonoids, phenols, leucoanthocyanidins, terpenes and steroids groups. Fluorescent SNP with high degree of agglomeration were observed by the microscopical technics used. A promising antibacterial activity of SNP was shown by a zone of microbial growth inhibition. These results suggested the need for going deeper in the physico-chemical characterization and kinetic studies, as well as the biological evaluations to make possible the use of this plant source in the future development of antibacterial formulations for bean seed protection.