الفهرس 
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Abstract
Gallibacterium anatis (G. anatis) is a Gram-negative bacterium of the Pasteurellaceae
family that resides normally in the respiratory and reproductive tracts in poultry and G.
anatis causes oophoritis, salpingitis, peritonitis, decreases egg production and
increased mortalities in layers. The aim of the current study was to detect the incidence
of G. anatis in layer chickens, isolation of G. anatis from poultry, biochemical
identification, antimicrobial sensitivity test of obtained strains, PCR detection of 16S
rRNA-23S rRNA and some antimicrobial resistance genes, detection of minimal
inhibitory concentrations (MIC) for antibiotics and plant extracts, Using decimal assay
for additivity (DAA) method to determine interaction effect between combination of
plant extracts and antibiotic methods and pathogenicity test of isolated G. anatis. The
total prevalence of G. anatis was 30% in the examined diseased layer chickens. By
disc diffusion method, the retrieved strains were resistant to doxycycline (98.3%),
amoxicillin (95.8%) and gentamycin (95%). But susceptible to erythromycin (95.8%),
florfenicol (90%), sulfamethoxazole- trimethoprim (57.5%) and difloxacin (44.17%).
By PCR using 16S rRNA and 23S rRNA specific primers for the G. anatis and were
tested for the presence of three resistance genes (blaROB, aphA1and tetH) and the
obtained results revealed that all tested strains (8/8, 100%) were positive for these
genes. The MIC of the methanolic extract of rosemary leaves was (64 µg/ml) and for
eucalyptus globules was 256 µg/ml, while for cinnamon was 1024 µg/ml. The current
study revealed that rosemary noted best results with combination with amoxicillin at
ratios 9:1 and 7:3. In addition to combination with doxycycline give acceptable results
at ratios 9:1, 8:2 and 7:3 but with florfenicol using give good results at ratios 9:1 and
8:2. Moreover in combination with erythromycin giving good results at ratios 9:1 and
8:2. While eucalyptus globules in combination with four antibiotics at ratios 9:1and 8:2
gave best results with amoxicillin, but for doxycycline was at three ratios (9:1, 8:2 and
7:3). In addition with florfenicol gave acceptable result at ratio 8:2. After intra nasal
(IN) of experimental infected chicks with G. anatis isolates, all chickens showed
depression, respiratory signs such as rales, coughing, sneezing, conjunctivitis and teary
eyes with a decreased feed and water intake. Treatment was effective by DAA method
by combination between doxycycline and rosemary at ratio 9:1. In addition to
amoxicillin and rosemary was very effective and for erythromycin in combination with
rosemary. Also florfenicol with rosemary at 9:1 .