Study On The Susceptibility And Resistance Mechanism Of Different Strains Of Mycoplasma Gallisepticum To Antibiotic Drugs

Mycoplasma gallisepticum (MG) is a primary pathogen which can induce chronicrespiratory disease (CRD) in chicken. It is a popular disease resulting in great economiclosses, severely influencing poultry industry. Because of frequently using or misusingantibiotic drugs, mycoplasma resistant strains constantly increasing, bring difficulties toclinical cure and medication, and due to the drug residues in livestock products, it also canbring dangers to public health. Therefore, understanding the resistance of MG and studyingits resistance mechanism have great importance to preventing and controlling CRD, andensuring the public health of livestock products.In this study, susceptibility tests of 20 MG clinical isolates to 6 antibiotics wereperformed by using broth microdilution method, according to the criteria of MIC toselect resistant strains, then used tetracycline to induce resistance. Polymerase chainreaction (PCR) was used to amplify the tetracycline resistance determinant (tetM) andgyrA gene, and gyrA gene was sequenced, then analyzing the sequence with ClustalXsoftware. And the correlation of nucleotide mutations with the resistance to quinoloneswas investigated. Sensitivity testing showed that, sensitivity of MG clinical strains toantibiotics have some area characteristics, and different strains from the same region areclose to each other. It probably associates with the frequent using of antibiotic drugs.The sequenced result of gyrA indicates that the ORDR of gyrA in some strains havebase mutations, some are silence mutation, not altering the amino acid. But somemutations lead to the change of amino acid, such as a G to T change at site 249 and a Tto G change at site 270, respectively, causing Ser to lie at 83 site and Val to Gly at 90site. The other strains also have different forms of amino acid mutation, inducingresistance of MG to quinolones.