الفهرس 
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Abstract
Mycoplasmosis constituted one of the most important diseases condition affecting poultry. M. gallisepticum infection combined with E. coli are accused for CRD in chicken yielding significant losses in economics to all sectors of poultry industry.
Antimicrobial abuse is considered to be the main cause to the appearance of antimicrobial resistant bacteria. Resistance to macrolides has been developed in recent years and occurs by different mechanisms: acquisition of resistance genes by horizontal transfer mediated by plasmids by target site methylation, inactivation by modifying enzymes as estrases and phosphotransferases and acquisition of efflux pump or nontransferable resistance due to mutation in 23S ribosomal RNA and this is considered as the only known mechanism accusing for resistance in bacteria with small number of rRNA operons as Mycoplasma.
Therefore this study aimed to throw spot of light upon the identification of bacteria causing CRD in chicken including M. gallisepticum and E. coli. It is also aimed to study their macrolide resistance mechanism, that could be achieved first phenotypicaly using MIC broth microdilution method then genotypically by PCR for detection of macrolide resistance genes among resistant isolates then sequencing to the obtained genes to correlate resistance phenotypes with mutations in macrolide resistant determining region.