الفهرس 
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Abstract
Mycoplasma gallisepticum (MG) is a persistent, highly transmissible chicken pathogen. It predisposes the birds to other infection yielding significant losses in performance and associated economics to all sectors of the poultry industry. Extensive application of fluoroquinolones such as enrofloxacin, ciprofloxacin and danofloxacin was the main cause of fluoroquinolones resistance. Emergence of resistance to fluoroquinolones is mainly due to chromosomal mutations in quinolone resistant determining regions (QRDRs) of genes encoding the subunits of the drug’s target enzymes, DNA gyrase and topoisomerase IV, which are essential for DNA replication. Therefore, this study was designed for molecular detection of mutation in QRDRs of fluoroquinolone resistant MG field isolates.
In the present work, 400 specimens (273 specimens from El-Sharkia and 127 from El-Dakahlia Governorates) were collected from broiler chickens with respiratory manifestations and not respond for treatment. The specimens were examined phenotypically for determination of minimum inhibitory concentration (MIC) of fluoroquinolones against M. gallisepticum field isolates by broth microdilution method and genotypically for molecular detection of MG virulence gene (mgc2 gene) and molecular detection of mutation in QRDRs of fluoroquinolones resistant MG field isolates.
Conventional methods for isolation and identification of Mycoplasma depended mainly on isolation of the microorganism