Abstract
We examined the antimicrobial susceptibilities of 52 Mycoplasma bovis isolated from cattle with respiratory disease and the nucleotide sequence of domain V in 23S ribosomal RNA (rRNA) associated with macrolide (ML) resistance. Resistance to tylosin (TS) was found in three isolates (5.8%). Of the three isolates, two (3.8%) were resistantce to lincomycin (LCM). The minimum inhibitory concentration (MIC) of tilmicosin ranged from ≦0.1 to ＞100μg/ml; 24 isolates exhibited a high MIC of tilmicosin (＞100μg/ml). Resistance to enrofloxacin and kanamycin were found in two and one isolates, respectively. All the isolates were susceptible to oxytetracycline, thiamphenicol, florfenicol, and tiamulin. Nucleotide sequencing revealed that one of the two TS-LCM-resistant strains had an A to G mutation at position 2058 in domain V of 23S rRNA. However, no mutations were detected in the domains of other ML-resistant or low-susceptible strains. These findings suggests that M. bovis may acquire ML resistance through alternative resistant mechanisms, in addition to mutations in domain V 23S rRNA.
