Citrus canker, caused by Xanthomonas citri subsp. citri, is a devastating disease that affects citrus production and trade worldwide. Traditional control methods, based on copper compounds, are effective but pose environmental and health risks due to their toxicity and potential for bioaccumulation. This study evaluates the synergistic potential of essential oils (EOs) and rhamnolipids as sustainable alternatives for disease management. Four EOS (citronella, palmarosa, geranium, and clove) were tested for their antibacterial activity. Citronella EO showed a 90% inhibitory concentration (IC 90) of 0.15% (v/v) and a minimum bactericidal concentration of 0.25% (v/v), while the other EOs showed IC 90 and bactericidal activity at 0.06% (v/v). Rhamnolipids (RHLs), biosurfactants produced by Pseudomonas aeruginosa, inhibited X. citri at a concentration of 0.3% (v/v). The combination of citronella EO and RHLs showed a synergistic effect, reducing the inhibitory concentration of citronella by 50% and that of RHLs by more than 90%. In addition, the combined formulation permeabilized more than 80% of bacterial membranes and reduced biofilm formation. In contrast, other oils tested in combination with rhamnolipid showed independent effects. These results indicate that EOs and rhamnolipids represent an environmentally safe strategy for the control of X. citri subsp. citri that overcomes the limitations of conventional methods while reducing environmental and health impacts.

The rise of antimicrobial-resistant pathogens has increased interest in biologically derived compounds for treating dermal infections. This study evaluates the effect of rhamnolipid, a biosurfactant produced by Pseudomonas aeruginosa, in combination with essential oils of oregano (Origanum vulgare), tea tree (Melaleuca alternifolia), and cinnamon (Cinnamomum cassia) against Cutibacterium acnes and Staphylococcus aureus, with or without incorporation into a sodium alginate-based film. Minimum bactericidal concentrations (MBC), biofilm inhibition development, and time-kill assays were used to assess antimicrobial activity. Results indicate MBCs of 800 mg/L for rhamnolipid, 0.05% for oregano, 0.2% for tea tree oil, and 0.5% for cinnamon against C. acnes. For S. aureus, the MBCs are 2500 mg/L, 0.07%, 0.3%, and 0.5%, respectively. When combined the rhamnolipids and the essential oils, the MBC for C. acnes were reduced to 500 mg/L of rhamnolipid and essential oils of oregano, tea tree and cinnamon were reduced to 0.03%, 0.1% and 0.3%, respectively, and for S. aureus were reduced to 1500 mg/L of rhamnolipid and essential oils of oregano, tea tree and cinnamon were reduced to 0.05%, 01% and 0.3%, respectively. A sodium alginate-based polymer film was formulated with rhamnolipid, maintaining antimicrobial efficacy and water-retention capacity but with reduced mechanical strength. These findings suggest a promising topical application for treating dermal infections.