الفهرس 
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Abstract
In the current study bacteriological examination of a total number of 120 liver samples of broiler chickens of ages (2-3weeks) that suffered from (septicemia, congested liver, necrotic foci on liver, Perihepatitis, air saculitis, pneumonia, peritonitis, enteritis, inflammation of the intestinal mucosa, inflammation of kidney, yolk sac inflammation, and typhlitis) revealed that 102 cases were harbored Gram-negative bacterial strains with an incidence of 85%.
Bacteriological examination showed that oxidase-negative bacteria were 78 (65%) of isolates including E. coli (20 isolates), S. Enteritidis (4 isolates), E. cloacae (25 isolates), C. freundii (17 isolates), P. vulgaris (5 isolates), K. pneumonae (3isolates), Shigella spp. (2 isolates), and S. marcescens (2 isolates) with incidence of 16.7%, 3.3%, 20.8%, 14.2%, 4.2%, 2.5%, 1.7%, and 1.7%, respectively. While 24 (20%) were oxidase-positive including P. aeruginosa (10 isolates), M. haemolytica (6 isolates), A. hydrophila (8 isolates) with an incidence of 8.3 %, 5%, and 6.7%, respectively.
The serological and molecular typing of 4 Salmonella isolates revealed that, all the isolates were serotyped as S. Enteritidis (100%) using multiplex PCR.
The in-vitro antimicrobial sensitivity test of 20 E. coli, 4 S. Enteritidis, 5 E. cloacae, 4 C. freundii, 10 P. aeruginosa, 6 M. haemolytica, and 8 A. hydrophila isolates against 14 antimicrobial agents revealed that the majority of E. coli isolates were multidrug resistance (MDR) with an incidence of (42.8%) and the highly resistant was recorded with (100%) to amoxicillin, cefalexin, ceftriaxone, streptomycin, Fosfomycin, and sulpha/trimethoprim. While S. Enteritidis MDR with an incidence of (71.4%) and the highly resistant was recorded with (100%) to amoxicillin, amoxicillin-clavulanic acid, cefalexin, ceftriaxone, cefotaxime, gentamycin, streptomycin, ciprofloxacin, doxycycline, and sulpha/
trimethoprim. The tested E. cloacae and C. freundii isolates were highly resistant to the most used antimicrobial agents. The tested isolates of P. aeruginosa were MDR with an incidence of (64.3%) and the highly resistant with (100%) to amoxicillin, amoxicillin-clavulanic acid, cefalexin, cefotaxime, apramycin, kanamycin, doxycycline, Fosfomycin, and sulpha/trimethoprim.
While M. haemolytica and A. hydrophila isolates were MDR with an incidence of 71.4% and 7.1%, respectively.
Biofilm formation has a great importance for public health, because of biofilm-associated bacterial agents. The biofilm formation on CRA was assessed for 16 isolates including (10 E. coli, 2 S. Enteritidis, and 4 P. aeruginosa) and revealed that the isolates were 100% Positive biofilm formation.
Due to extensive usage of antibiotics and presence of highly resistance strains, the antimicrobial activity of cinnamon, oregano, clove, eucalyptus, and turmeric oils were tested at concentrations of (0.1%, 0.01%, and 0.05%) against 23 MDR isolates including (10 E. coli, 4 S. Enteritidis, 4 P. aeruginosa, and 5 M. haemolytica).
The results revealed that cinnamon and oregano oils exhibited significant inhibitory effect at concentration of 0.1% on all tested isolates. While cinnamon E.O exhibited a significant inhibitory effect at concentration of 0.01% only on 25% of S. Enteritidis.
The virulence of E. coli was examined by PCR for virulence genes iutA, fimH, papC, fimA, tsh, and felA with a percentage of 100%, 100%, 75%, 75%, 50%, and 25%. Meanwhile, the virulence of S. Enteritidis was assessed by PCR for biofilm-related genes adrA and csgD with a percentage of 100% of each.
Also, the virulence of P. aeruginosa was assessed by PCR for biofilm-related genes pslA and pelA with a percentage of 100% of each.
S. Enteritidis and P. aeruginosa tested isolates were harbored to ᵝ-lactamase-encoding gene (blaTEM) and sulfonamide resistance gene (sul1) with a percentage of 100% of each.
Biofilm process includes up-and down regulation of several virulence genes that responsible for adhesion, secretion of extracellular matrix, and detachment. The expression of biofilm-related genes (csgD gene of S. Enteritidis and pslA of P. aeruginosa) was applied by quantitative RT-PCR.