In vitro antimicrobial susceptibility of Mycoplasma bovis isolated in Israel from local and imported cattle.

Monitoring of susceptibility to antibiotics in field isolates of pathogenic bovine mycoplasmas is important for appropriate choice of treatment. Our study compared in vitro susceptibility profiles of Mycoplasma bovis clinical strains, isolated during 2005-2007 from Israeli and imported calves. Minimal inhibitory concentration (MIC) values were determined for macrolides by the microbroth dilution test, for aminoglycosides by commercial Etest, and for fluoroquinolones and tetracyclines by both methods. Notably, although correlation between the methods was generally good, it was not possible to determine the MIC endpoint for enrofloxacin-resistant strains (MIC > or =2.5 microg/ml in the microtest) by Etest. Comparison of antibiotic susceptibility profiles between local and imported M. bovis strains revealed that local strains were significantly more resistant to macrolides than most isolates from imported animals, with MIC(50) of 128 microg/ml vs. 2 microg/ml for tilmicosin and 8 microg/ml vs. 1 microg/ml for tylosin, respectively. However, local strains were more susceptible than most imported strains to fluoroquinolones and spectinomycin. Difference in susceptibility to tetracycline, doxycycline and oxytetracycline between local and imported strains was expressed in MIC(90) values for imported strains in the susceptible range compared to intermediate susceptibility for local strains. The marked difference in susceptibility profiles of M. bovis strains isolated from different geographical regions seen in this study emphasizes the necessity for performing of the antimicrobial susceptibility testing periodically and on a regional basis.