Antimicrobial and Antivirulence Action of Eugenia brejoensis Essential Oil in vitro and in vivo Invertebrate Models.

Eugenia brejoensis L. (Myrtaceae) is an endemic plant from caatinga ecosystem (brazilian semi-arid) which have an E. brejoensis essential oil (EbEO) with reported antimicrobial activity. In this work, in vitro and in vivo models were used to characterize the inhibitory effects of EbEO in relation to Staphylococcus aureus. EbEO inhibited the growth of all tested S. aureus strains (including multidrug resistance isolates) with values ranging from 8 to 516 µg/mL. EbEO also synergistically increased the action of ampicillim, chloramphenicol, and kanamycin. The treatment with subinhibitory concentrations (Sub-MIC) of EbEO decreased S. aureus hemolytic activity and its ability to survive in human blood. EbEO strongly reduced the levels of staphyloxanthin (STX), an effect related to increased susceptibility of S. aureus to hydrogen peroxide. The efficacy of EbEO against S. aureus was further demonstrated using Caenorhabditis elegans and Galleria mellonella. EbEO increased the lifespan of both organisms infected by S. aureus, reducing the bacterial load. In addition, EbEO reduced the severity of S. aureus infection in G. mellonella, as shown by lower levels of melanin production in those larvae. In summary, our data suggest that EbEO is a potential source of lead molecules for development of new therapeutic alternatives against S. aureus.

Schinus terebinthifolia leaf lectin (SteLL) has anti-infective action and modulates the response of Staphylococcus aureus-infected macrophages.

Staphylococcus aureus is recognized as an important pathogen causing a wide spectrum of diseases. Here we examined the antimicrobial effects of the lectin isolated from leaves of Schinus terebinthifolia Raddi (SteLL) against S. aureus using in vitro assays and an infection model based on Galleria mellonella larvae. The actions of SteLL on mice macrophages and S. aureus-infected macrophages were also evaluated. SteLL at 16 µg/mL (8 × MIC) increased cell mass and DNA content of S. aureus in relation to untreated bacteria, suggesting that SteLL impairs cell division. Unlike ciprofloxacin, SteLL did not induce the expression of recA, crucial for DNA repair through SOS response. The antimicrobial action of SteLL was partially inhibited by 50 mM N-acetylglucosamine. SteLL reduced staphyloxathin production and increased ciprofloxacin activity towards S. aureus. This lectin also improved the survival of G. mellonella larvae infected with S. aureus. Furthermore, SteLL induced the release of cytokines (IL-6, IL-10, IL-17A, and TNF-α), nitric oxide and superoxide anion by macrophagens. The lectin improved the bactericidal action of macrophages towards S. aureus; while the expression of IL-17A and IFN-γ was downregulated in infected macrophages. These evidences suggest SteLL as important lead molecule in the development of anti-infective agents against S. aureus.

Anti-staphylococcal activity of Syagrus coronata essential oil: Biofilm eradication and in vivo action on Galleria mellonela infection model.

In this study, essential oil extracted from Syagrus coronata seeds (SCEO) was evaluated for antibacterial and antibiofilm activities against Staphylococcus aureus; in addition, Galleria mellonella model was used as an in vivo infection model. SCEO was mainly composed by fatty acids (89.79%) and sesquiterpenes (8.5%). The major components were octanoic acid, dodecanoic acid, decanoic acid and γ-eudesmol. SCEO showed bactericidal activity (minimal bactericidal concentration from 312 to 1250 µg/mL) against all tested S. aureus clinical isolates, which showed distinct biofilm-forming and multiple drug resistance phenotypes. SCEO weakly reduced biomass but remarkably decreased cell viability in pre-formed biofilms of S. aureus isolate UFPEDA-02 (ATCC-6538). Electron microscopy analysis showed that SCEO treatments decreased the number of bacterial cells (causing structural alterations) and lead to loss of the roughness in the multiple layers of the three-dimensional biofilm structure. In addition, overproduction of exopolymeric matrix was observed. SCEO at 31.2 mg/kg improved the survival of G. mellonela larvae inoculated with UFPEDA-02 isolate and reduced the bacterial load in hemolymph and melanization. In conclusion, SCEO is an antibacterial agent against S. aureus strains with different resistance phenotypes and able to disturb biofilm architecture. Our results show SCEO as a potential candidate to drug development.