title: Evaluation of canine-specific minocycline and doxycycline susceptibility breakpoints for meticillin-resistant Staphylococcus pseudintermedius isolates from dogs.
abstract: BACKGROUND
  Using the US Clinical and Laboratory Standards Institute (CLSI) human tetracycline breakpoints to predict minocycline and doxycycline susceptibility of Staphylococcus pseudintermedius (SP) isolates from dogs is not appropriate because they are too high to meet pharmacokinetic/pharmacodynamic data using a standard dose. New breakpoints have been approved for doxycycline and proposed for minocycline. Revised breakpoints are four dilutions lower than tetracycline breakpoints, providing a more conservative standard for classification of isolates.
  
  
  OBJECTIVE
  The objectives of this study were to measure minimum inhibitory concentrations (MICs) of minocycline and doxycycline of 100 canine meticillin-resistant SP clinical isolates, compare their susceptibilities to minocycline and doxycycline based on current and revised standards, and document their tetracycline resistance genes.
  
  
  METHODS
  E-test strips were used to determine MICs. PCR was used to identify tet genes.
  
  
  RESULTS
  Using the human tetracycline breakpoint of MIC ≤ 4 μg/mL, 76 isolates were susceptible to minocycline and 36 isolates were susceptible to doxycycline. In contrast, using the proposed minocycline breakpoint (MIC ≤ 0.25 μg/mL) and approved doxycycline breakpoint (MIC ≤ 0.125 μg/mL), 31 isolates were susceptible to both minocycline and doxycycline. Thirty-one isolates carried no tet genes, two had tet(K) and 67 had tet(M).
  
  
  CONCLUSIONS
  Use of the human tetracycline breakpoints misclassified 45 and five of the isolates as susceptible to minocycline and doxycycline, respectively. PCR analysis revealed that 43 and five of the isolates classified as susceptible to minocycline and doxycycline, respectively, possessed the tetracycline resistance gene, tet(M), known to confer resistance to both drugs. These results underscore the importance of utilizing the proposed minocycline and approved doxycycline canine breakpoints in place of human tetracycline breakpoints.
authors.affiliation: Department of Veterinary Clinical Sciences, College of Veterinary Medicine, The Ohio State University, 601 Vernon L. Tharp St., Columbus, OH, 43210, USA.
authors.forename: Melanie L
authors.initials: ML
authors.lastname: Hnot
authors.affiliation: Department of Veterinary Clinical Sciences, College of Veterinary Medicine, The Ohio State University, 601 Vernon L. Tharp St., Columbus, OH, 43210, USA.
authors.forename: Lynette K
authors.initials: LK
authors.lastname: Cole
authors.affiliation: Department of Veterinary Clinical Sciences, College of Veterinary Medicine, The Ohio State University, 601 Vernon L. Tharp St., Columbus, OH, 43210, USA.
authors.forename: Gwendolen
authors.initials: G
authors.lastname: Lorch
authors.affiliation: Department of Molecular Biomedical Sciences, College of Veterinary Medicine, North Carolina State University, 1060 William Moore Drive, Raleigh, NC, 27607, USA.
authors.forename: Mark G
authors.initials: MG
authors.lastname: Papich
authors.affiliation: Department of Veterinary Preventive Medicine, College of Veterinary Medicine, The Ohio State University, 601 Vernon L. Tharp St., Columbus, OH, 43210, USA.
authors.forename: Paivi J
authors.initials: PJ
authors.lastname: Rajala-Schultz
authors.affiliation: Department of Veterinary Clinical Sciences, College of Veterinary Medicine, The Ohio State University, 601 Vernon L. Tharp St., Columbus, OH, 43210, USA.
authors.forename: Joshua B
authors.initials: JB
authors.lastname: Daniels
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000627:therapeutic use*; D004283:Dog Diseases / Q000188:drug therapy* / Q000382:microbiology; D004285:Dogs / Q000382:microbiology; D004318:Doxycycline / Q000627:therapeutic use*; D016106:Methicillin Resistance; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects*; D008826:Microbial Sensitivity Tests / Q000662:veterinary; D008911:Minocycline / Q000627:therapeutic use*; D013207:Staphylococcal Skin Infections / Q000188:drug therapy / Q000382:microbiology / Q000662:veterinary*; D057789:Staphylococcus intermedius / Q000187:drug effects* / Q000235:genetics
chemical_list: D000900:Anti-Bacterial Agents; D008911:Minocycline; D004318:Doxycycline