Targeting endocarditis-associated Streptococcus biofilms: The antibacterial potential of Lippia sidoides essential oil.

OBJECTIVES: Streptococcus species such as Streptococcus sanguinis and Streptococcus gordonii are key contributors to infective endocarditis due to their ability to form resilient biofilms. This study evaluated the antibacterial and antibiofilm potential of Lippia sidoides essential oil (LSEO) against clinical isolates obtained from blood and the oral cavity. DESIGN: Sixteen clinical isolates of S. sanguinis and S. gordonii, comprising eight oral isolates and eight blood isolates obtained from patients with infective endocarditis, were evaluated. Antimicrobial activity was determined using minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) assays. Antibiofilm activity was assessed through inhibition and viability reduction of 18-hour biofilms, and effects on initial biofilm formation were analyzed by scanning electron microscopy (SEM). Cytotoxicity was evaluated in human gingival fibroblasts (HGF), and systemic toxicity was assessed using Galleria mellonella larvae. RESULTS: Gas chromatography identified carvacrol as the major compound of LSEO. The oil exhibited pronounced antibacterial activity against both oral and bloodstream isolates, with MIC values ranging from 0.1562 to 1.25 mg/mL against both species. LSEO inhibited biofilm formation by 30-96% and reduced biofilm viability by 4-100%, showing antibiofilm activity comparable to chlorhexidine under the experimental conditions. SEM analysis revealed marked disruption of early biofilm architecture. Toxicity assays demonstrated that LSEO was non-cytotoxic to HGF cells at MIC and MIC× 2 and exhibited low systemic toxicity in Galleria mellonella. CONCLUSIONS: LSEO demonstrated potent antibacterial and antibiofilm effects against endocarditis-associated Streptococcus isolates while maintaining a favorable safety profile, highlighting its potential as a natural strategy for preventing biofilm-related infections.