Pseudomonas aeruginosa (P. aeruginosa) is considered as an important pathogen that threatens poultry industry resulting in severe economic losses. The ability of this pathogen to form biofilm and resistance to the antimicrobial agents represents a very great danger that produces treatment difficulties. So that, this study was conducted to isolate P. aeruginosa from 100 diseased broiler chickens farms in Dakahlia Governorate and studied the in vitro and in vivo antibacterial and anti-biofilm activities of Eucalyptus extract on P. aeruginosa. P. aeruginosa were isolated from 100 diseased broiler chickens farms in Dakahlia Governorate with a percentage of (12%) and it showed higher resistance to amoxicillin/clavulanic (91.7%), ampicillin/sulbactam (83.3%), doxycycline and erythromycin (75% for each). Eight P. aeruginosa isolates were strong biofilm producers (8/12, 66.7%) and 4 isolates (4/12, 33.3%) were moderate. The in vitro antibacterial and anti-biofilm activities of Eucalyptus extract on the isolated P. aeruginosa showed the higher activities of 50, 75 and 100 mg/ 1ml concentrations than 40 mg/ 1ml. The in vivo studies in experiment (1) showed (100%) hatchability with no embryonic mortalities in the inoculated groups with the Eucalyptus extract. In experiment (2), the study showed that inoculating group 5 with a 100 mg/ml concentration of Eucalyptus extract in-ovo had beneficial effects. It prevented deaths, lessened clinical symptoms, enhanced growth performance, and reduced P. aeruginosa colonization in internal organs compared to group 3 (inoculated with 50 mg/ml) and group 4 (inoculated with 75 mg/ml).
The expression of pslA gene (responsible for biofilm formation) was examined using RT- PCR and the results showed significant down regulation (decrease in the expression or activity of a gene) in the examined liver of chicks in group (5) in comparison with other groups. The obtained results suggested that application of Eucalyptus extract in-ovo inoculation is an alternative natural approach to control P. aeruginosa characterized by multidrug resistance and biofilm formation in broiler farms.