Biofilm Formation and Inhibitory Effect of Essential Oils in Multidrug-Resistant Pseudomonas aeruginosa

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Biofilm formation is a major concern in medicine, as well as in the food industry. Some infections related to bacterial biofilms such as Pseudomonas aeruginosa are a real public health challenge. This study aimed to show the activity of essential oils on P. aeruginosa biofilm formation. Pseudomonas aeruginosa isolates consisting of animal (100), environmental (20) and clinical strains (42) were identified by PCR and sequenced. Biofilm formation was assessed by the microplate method. Antibiotic susceptibility testing was performed by using Kirby–Bauer disc-diffusion method. The average biofilm formation percentages vary from 1.2 to 2.1 in 24h and from 2.3 to 3.2 in 48h. The median biofilm formation value was higher in environmental strains (1.4 ± 0.2) than in clinical (1.2 ± 0.4) and animal (1.1 ± 0.4). In decreasing order of importance, the essential oils of Mentha piperita (90 ± 5.12% at 100%), Eucalyptus globulus (34 ± 0.08% at 100%) and Lavandula angustifolia (12 ± 0.71% to 100%) showed distinct inhibitory effects on biofilm formation (p <0.05). The rate of resistance of P. aeruginosa to the antibiotics imipenem, ceftazidime, cefepime, fosfomycin and colistin varied from 12.7% to 48.4% in the biofilm status while that of plankton cells ranged from 2.3% to 15.0%. Moreover, resistance to ticarcillin, ticarcillin clavulanic acid, piperacillin and ciprofloxacin ranged from 56.4% to 83.1% in biofilm and from 29.4% to 51.4% in planktonic cells. In general, biofilm is more resistant to different antibiotics than free cells. The tested essential oils could be an effective natural control against microbial biofilm formation.