Activity of 5 plant-derived compounds against Pseudomonas aeruginosa and Burkholderia cepacia clinical isolates related to respiratory tract infections

Introduction. The vegetal world constitutes an immense factory of compounds with antimicrobial properties. This study aimed to evaluate the antimicrobial activity of 5 plant-derived compounds (cinnamaldehyde, carvacrol, eugenol, geraniol and ß-citronellol) against Pseudomonas aeruginosa and Burkholderia cepacia strains isolated from patients suffering from respiratory tract infections at Marqués de Valdecilla University Hospital. Material and Methods. Five strains of P. aeruginosa and five B. cepacia complex strains (including B. multivorans and B. contaminans) were included. The activity of the 5 compounds was assayed using disc diffusion method and Minimum Inhibitory Concentration (MIC) was determined by means of agar diffusion method. The biofilm-forming ability of the 10 clinical strains was evaluated using the crystal violet assay and through confocal laser microscopy. Cinnamaldehyde’s anti-biofilm activity was tested using sub-inhibitory concentrations (C=MIC/2). The activity of 7 antibiotics in combination with cinnamaldehyde was measured looking for synergistic effects. Results. Cinnamaldehyde showed the highest antibacterial activity against both pathogens with MIC values of 197 mg/mL, 0.1875% (v/v) [P. aeruginosa] and 32.6 mg/mL, 0.031% (v/v) [B. cepacia], respectively. Pseudomonas aeruginosa and Burkholderia multivorans showed high biofilm-formation capacity, whereas Burkholderia contaminans did not. Cinnamaldehyde at sub-inhibitory concentrations reduced the biofilm formation of both pathogens. The activity of the tested antibiotics (gentamicin, levofloxacin, tetracycline, linezolid, ceftaroline, vancomycin and rifampicin) was not increased in the presence of cinnamaldehyde. Conclusions. Cinnamaldehyde showed promising results as an antibacterial compound against P. aeruginosa and B. cepacia clinical isolates. These results must be confirmed with broader sampling, including multidrug-resistant clones.Máster en Biología Molecular y Biomedicin