title: Susceptibility of Arcanobacterium pyogenes from different sources to tetracycline, macrolide and lincosamide antimicrobial agents.
abstract: Chlortetracycline, oxytetracycline, and the macrolide, tylosin, are extensively used for growth promotion and disease prophylaxis in the cattle and swine industries in the US. Arcanobacterium pyogenes, a common inhabitant of the mucosal surfaces of cattle and swine, is also a pathogen associated with a variety of infections in these animals. A broth microdilution technique was used to determine the antimicrobial susceptibility of 48 A. pyogenes isolates to macrolides, lincosamides and tetracyclines. The MIC50 and MIC90 for chlortetracycline were 0.12 and 8 mg/l, respectively. Similarly, the MIC50 and MIC90 for oxytetracycline were 0.25 and 8 mg/l, while the MIC50 and MIC90 for tetracycline were 0.25 and 16 mg/l, respectively. The MIC50 and the MIC90 were < or = 0.06 and >64 mg/l, respectively, for erythromycin, tylosin and clindamycin. This resistance pattern indicated that some of these A. pyogenes isolates may carry an MLS(B) resistance determinant. A. pyogenes isolates (12.5%) were resistant to erythromycin, and this percentage doubled when MICs were performed following induction with erythromycin. Of the 48 A. pyogenes isolates, 25 and 41.7% were resistant to MLS(B) antimicrobial agents and the tetracycline derivatives, respectively. MLS(B) resistance was present in 22.2 and 35.3% of A. pyogenes isolates of bovine (n=27) or porcine (n=17) origin. In contrast, 70.6% of porcine isolates were resistant to the tetracyclines, compared with 25.9% of bovine isolates. These data suggest that a large proportion of A. pyogenes field isolates may be resistant to these commonly used antimicrobial agents.
authors.affiliation: Department of Veterinary Science and Microbiology, The University of Arizona, 1117 East Lowell Street, Tucson, AZ 85721, USA.
authors.forename: Hien T
authors.initials: HT
authors.lastname: Trinh
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Billington
authors.forename: Adam C
authors.initials: AC
authors.lastname: Field
authors.forename: J Glenn
authors.initials: JG
authors.lastname: Songer
authors.forename: B Helen
authors.initials: BH
authors.lastname: Jost
mesh_terms: D000191:Actinomycetaceae / Q000187:drug effects*; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D018942:Macrolides; D008826:Microbial Sensitivity Tests; D013754:Tetracyclines / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D018942:Macrolides; D013754:Tetracyclines