Development Of Macrolide Resistance In Mycoplasma Gallisepticum And Analysis Of Mutation On Resistant Gene

Erythromycin-resistant mutants and tilmicosin-resistant mutants were obtained in vitro from mycoplasma gallisepticum(MG)S6 and BG44T by increasing concemtrations of erythromycin and tilmicosin.The MICs of erythromycin for erythromycin-resistant S6 and BG44T are more than 436.7 u g/ ml. The MICs of tilmicosin for tilmicosin-resistant S6 and BG44T are more than 400 u g/ ml. Erythromycin-resistant S6 and BG44T showed cross-resistance to tilmicosin,tylosin and lincomycin. Tilmicosin-resistant S6 and BG44T showed cross-resistance to erythromycin,tylosin and lincomycin.Resistance by ribosomal mutations in domain V of 23S rRNA has been described.To determine the role of 23S rRNA in macrolide resistance in MG,we firstly differentiated the 23 S rRNA gene in the two ribosomal operons in MG(These two genes were named by 23rrnl and 23rrn2 respectively in mis article).MG DNA was digested by a restrictive endonuclease.electrophoresed in agarose gel, and transfered the DNA from the agarose gel to nylon membrane.To ascertain the positions of the two 23S rRNA genes,Southern hybridization was performed. 23S rRNA genes from the agarose gel were isolated, amplified, and cloned of 23S rRNA V genes were performed from isolated 23S rRNA genes.Cloned these genes.Within the 23rrnl, erythromycin-resistant S6 contained the 2058 mutation that was associated with resistance. For erythromycin-resistant S6, 23rrn2 was unchanged.And for tilmicosin-resistant S6, 23rrnl was unchanged and 23rrn2 harbored 2058,2504 mutation that was associated with resistance. Erythromycin-resistant BG44T occurred 2458 resistant point mutation in 23rrnl that was associated with resistance and 2057 , 2058 resistant point mutation that was associated with resistance in 23rrn2.Tilmicosin-resistant BG44T did not show resistant point mutation in 23rrnl and 2504,2058 point mutation that was associated with resistance in 23rrn2.