Staphylococcus aureus is a nosocomial bacterium causing different infectious diseases, ranging from skin and soft-tissue infections to more serious and life-threatening infections such as sepsis, meningitis and endocarditis, which may be exacerbated by antibiotic resistance. Plant products may be seen as an alternative as antibacterial agents, namely, against S. aureus. Thus, the aim of this work was to characterize the chemical composition and evaluate the bioactive properties of the T. zygis essential oil (EO), with a focus on antimicrobial activity against S. aureus. Gas chromatography coupled with mass spectrometry was used to assess the chemical composition of the T. zygis EO, and the antioxidant activity was evaluated using the DPPH method and β-carotene-bleaching assay. The antimicrobial activity against S. aureus strains, the interaction with different antibiotics and the attenuation of this bacterium’s virulence were evaluated. The T. zygis EO showed antioxidant activity acting through two different mechanisms and antibacterial activity against S. aureus, with antibiofilm and antihaemolytic properties. This EO also demonstrated synergistic or additive interactions in combination with ampicillin, ciprofloxacin or vancomycin against S. aureus strains and, in some cases, changed the antibiotic-resistance phenotype from resistant to susceptible. Therefore, the present work demonstrates the good bioactive properties of the EO of T. zygis, mainly the antimicrobial activity against S. aureus, revealing its potential to be used as an antibacterial agent.

The plants used in folk medicine have been increasingly studied to identify their bioactive properties. Therefore, this study aimed to assess the bioactivity of the hydroethanolic extracts of plants collected in Gardunha Mountain, Portugal. Seven abundant and representative wild plants were studied: Cistus salviifolius, Clinopodium vulgare, Coincya monensis, Glandora prostrata, Helichrysum stoechas, Rubia peregrina, and Umbilicus rupestris. The phytochemical composition of the extracts was determined by UHPLC-timsTOF-MS and by spectrophotometric methods. The antioxidant, in vitro anti-inflammatory and antimicrobial activity and the biocompatibility of the extracts were tested. The extracts were predominantly composed of flavonoids and phenolic acids, such as gallic acid, neochlorogenic acid and quercetin glycosides. The C. salviifolius extracts demonstrated very strong antioxidant activity related to scavenging free radicals (AAI = 2.84 and 2.93). Regarding antimicrobial activity, the H. stoechas extract exhibited inhibitory effects, particularly against Gram-positive bacteria and yeasts (MIC = 0.008–0.5 mg/mL). The C. monensis, R. peregrina, and U. rupestris extracts showed low cytotoxicity (viability > 70%) in the highest concentration tested. These findings highlight C. salviifolius and H. stoechas as promising sources of novel bioactive compounds, particularly antimicrobials in controlling microbial growth and promoting associated health benefits, and underscore the value of traditional medicinal plants as a guide for pharmacological studies.

This study aimed to evaluate the antibacterial activity of Cistus salviifolius L. and Helichrysum stoechas (L.) DC extracts against S. aureus, including methicillin-resistant S. aureus (MRSA) strains. To this end, assays were conducted to assess killing kinetics, antibiotic combination effects, modulatory effects on ethidium bromide, inhibition of quorum sensing, and biofilm formation. H. stoechas extract demonstrated the strongest activity, with MIC values ranging from 7.8 to 62.5 µg/mL. When combined with antibiotics such as ampicillin, ciprofloxacin, or vancomycin, the extracts of C. salviifolius and H. stoechas predominantly exhibited synergistic (FICI value ≤ 0.5) or additive effects (0.5 < FICI ≤ 1), with some combinations resensitizing resistant strains. The aerial parts of C. salviifolius displayed modulatory effects on ethidium bromide MIC, reducing the concentration from 32 to 8 µg/mL, suggesting efflux pump inhibitory activity. In addition, this extract displayed slight quorum-sensing inhibition at a concentration of 125 µg/mL. Moreover, C. salviifolius and H. stoechas extracts inhibit the formation of biofilm by S. aureus strains, even at subinhibitory concentrations (0.5× and 0.25× MIC). The presence of compounds such as myricetin 3 O-galactoside, catechin derivatives, gallic acid, kaempferol, and chlorogenic acid in the extracts may contribute to their anti-Staphylococcus activity. These results demonstrated the dual antimicrobial and antivirulence potential of C. salviifolius and H. stoechas extracts, highlighting their promise as therapeutic agents or adjuvants against S. aureus. These extracts can be promising candidates for further studies on the development of novel strategies targeting multiple pathogenic pathways.