Effect of Essential Oils on Biological Criteria of Gram-Negative Bacterial Pathogens Isolated from Diseased Broiler Chickens

Abstract

The present study aimed to investigate Gram-negative bacterial pathogens isolated from liver affections in broiler chickens. The antibacterial effect of some essential oils (EOs) and their effects on isolated bacteria's biological and phenotypic criteria were also investigated. One hundred and twenty liver samples were subjected to bacterial isolation, biochemical and molecular identification of the isolated bacteria. The antibacterial effect of cinnamon, oregano, clove, turmeric, and eucalyptus EOs at different concentrations was evaluated using the agar dilution method. Pre-and Post EOs treatment biological activity (motility, biofilm formation, antimicrobial resistance, and virulence gene detection or expression) were evaluated in selected bacteria. Results revealed 85% prevalence of Gram-negative bacteria, including Escherichia coli (E. coli), Pseudomonas aeruginosa (P. aeruginosa), Mannheimia haemolytica (M. haemolytica), Aeromonas hydrophila (A. hydrophila) and Salmonella enteritidis (S. enteritidis). Most isolates were multiple antibiotic resistant, including quinolones and fosfomycin antimicrobials. A 0.1% concentration of cinnamon and oregano EOs effectively inhibited the growth of 80-100% and 50-100% of the tested bacterial spp, respectively; however, clove, turmeric, and eucalyptus EOs had no effect. Interestingly, after treatment with oregano or cinnamon oils, few of the resistant S. enteritidis, E. coli, and P. aeruginosa isolates were susceptible or intermediately sensitive to some antimicrobials. Similarly, the motility of S. enteritidis and, to a more extent P. aeruginosa was significantly reduced. Both EOs had no significant effect on S. enteritidis biofilm-forming ability; however, they inhibited the biofilm-forming ability of 10% and 100% of the tested E. coli and P. aeruginosa isolates, respectively. Standard PCR and real-time quantitative PCR did not reveal any significant change of either detection or differential expression of selected genes in the treated isolates. In conclusion, EOs are promising alternatives to minimize synthetic antimicrobials against multiple antibiotic-resistant bacteria. Finally, the antibacterial activity of EOs are mainly attributed to the induced structural disturbances in the treated bacteria.