الفهرس 
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Abstract
The present study was carried out to assess the incidence of
Pseudomonas aeruginosa and Staphylococcus aureus biofilm-producers in dairy farms and to evaluate the anti-biofilm activity of carvacrol and cinnamon essential oils (EOs) and their nanoemulsions (NEs) against the formed biofilms. Therefore, a total of 150 swab samples were collected from 3 different dairy farms (50 each) distributed in Assiut governorate (farm A) and El-Minia governorate (farms B and C), Egypt. The swabs were taken from different locations in the dairy farms from teats of dairy animals, milking machines, milk cooler tanks, milker’s hands, milking stanchions, milk utensils, milk strainers, and farm stanchions. The samples were examined bacteriologically for the isolation of Ps.
aeruginosa and Staph. aureus.
The bacteriological examination revealed that 10 samples (6.67%) were positive for Ps. aeruginosa; represented as 14, 2, and 4% in the farms A, B, and C, respectively; and the overall incidence of Staph.
aureus was 12.67% (19 samples) represented as 4, 30, and 4% in farms A, B, and C, respectively.
All the recovered Ps. aeruginosa and Staph. aureus strains were
seeded on Congo red agar (CRA) media to detect their biofilm-forming
ability. Two strains (20%) of Ps. aeruginosa and 4 strains (21%) of Staph. aureus was considered a biofilm producer and the rest strains were considered nonbiofilm producers. The 6 strains (2 Ps. aeruginosa and 4
Staph. aureus) were assessed for biofilm formation capacity by using the microtiter plate method. The quantification of the biofilms based on average optical density (OD) values was determined at 570 nm, which
revealed the 2 Ps. aeruginosa strains as moderate biofilm producers,
while the 4 Staph. aureus strains were categorized as 2 strong biofilm producers and 2 moderate biofilm producers.
The nanoemulsions (NEs) of carvacrol and cinnamon were prepared; and the characterization of NEs involved the assessments of their droplet size (nm) and polydispersity index (PDI) by using Zetasizer, their constituents by Fourier-transform infrared spectroscopy (FTIR) and the morphology by transmission electron microscopy (TEM). The results of NEs characterization showed the prepared carvacrol NE had droplet size 276.45±78.29 nm with PDI 0.172 while the prepared cinnamon NE had droplet size 321.05±68.75 nm with PDI 0.224 by Zetasizer. The TEM results revealed that the prepared carvacrol NE had a droplet size of 78.52±26.84 nm and the prepared cinnamon NE had a droplet size of 95±45.31 nm.
The antibacterial activity of carvacrol and cinnamon EOs and their NEs was evaluated against the 6 tested strains of Ps. aeruginosa and
Staph. aureus. Based on the agar well diffusion method results, the chosen MIC of carvacrol EO and its NE was 1.56% for both strains, and the MIC of cinnamon EO and its NE was 3.125% for both strains.
The antibiofilm activity of carvacrol and cinnamon EOs and their NEs was investigated by CRA and polystyrene methods against the 6 tested Ps. aeruginosa and Staph. aureus strains at the chosen MICs. The screening findings for the inhibition of biofilm formation by CRA
revealed that carvacrol and cinnamon EOs and NEs inhibit the biofilm formation of the 2 Ps. aeruginosa strains at MICs of 1.56 and 3.125%, respectively. On the other hand, the cinnamon EO inhibited the biofilm of
all 4 Staph. aureus strains together but carvacrol EO, carvacrol NE, and cinnamon NE failed to inhibit the biofilm of all the 4 tested Staph. aureus
strains together, which inhibited some of them and failed to the others.
The effect of carvacrol and cinnamon EOs and NEs on the dispersal of the already formed biofilms was studied using the polystyrene method, and the results revealed that the eradication of the performed biofilms was done using the carvacrol EO & its NE for both the tested strains of Ps. aeruginosa and Staph. aureus; while the cinnamon eradicated the pre-formed biofilm by its EO only for Staph.
aureus.