title: Evaluation of the Impact of Methicillin-Resistant Staphylococcus pseudintermedius Biofilm Formation on Antimicrobial Susceptibility.
abstract: OBJECTIVE
  To compare the minimum inhibitory concentration (MIC) of four antimicrobials in planktonic vs. biofilm-associated Staphylococcus pseudintermedius.
  
  
  METHODS
  In vitro study.
  
  
  METHODS
  78 isolates from dogs colonized or infected with methicillin-resistant S. pseudintermedius (MRSP, n=39) or methicillin-susceptible S. pseudintermedius (MSSP, n=39).
  
  
  METHODS
  Agar dilution was used to determine the MIC of amikacin, cefazolin, enrofloxacin, and gentamicin for planktonic bacteria. A modified broth microdilution assay was used to assess the MIC of biofilm-associated bacteria.
  
  
  RESULTS
  MIC were significantly higher in biofilm-associated vs. planktonic bacteria for all antimicrobials; amikacin (median MIC: biofilm >2,000 μg/mL vs. planktonic 3 μg/mL, P<.0001), cefazolin (>1,000 vs. 0.5 μg/mL, P<.0001), enrofloxacin (>1,000 vs. 0.25 μg/mL, P<.0001), and gentamicin (>1,000 vs. 0.3 μg/mL, P<.001). For all antimicrobials, there were significant differences in planktonic MIC for MRSP and MSSP (all P<.0001) but no differences between biofilm MIC for MRSP and MSSP (P=.08-1.0).
  
  
  CONCLUSIONS
  The MIC for biofilm-associated S. pseudintermedius are significantly higher than for planktonic bacteria. Standard methods for determining MIC are not appropriate for biofilm-associated infections. This must be considered when determining treatment regimens for infections that potentially involve biofilms, and further study of methods to control biofilm-associated infections is needed.
authors: Department of Clinical Studies, Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada.
authors: Meagan
authors: M
authors: Walker
authors: Department of Clinical Studies, Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada. amsingh@uoguelph.ca.
authors: Ameet
authors: A
authors: Singh
authors: Department of Clinical Studies, Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada.
authors: Alim
authors: A
authors: Nazarali
authors: Department of Clinical Studies, Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada.
authors: Thomas W G
authors: TW
authors: Gibson
authors: Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada.
authors: Joyce
authors: J
authors: Rousseau
authors: Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada.
authors: J Scott
authors: JS
authors: Weese
mesh_terms: D000583:Amikacin / Q000494:pharmacology; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D018441:Biofilms / Q000187:drug effects*; D002170:Canada; D002437:Cefazolin / Q000494:pharmacology; D004283:Dog Diseases / Q000188:drug therapy / Q000382:microbiology*; D004285:Dogs; D000077422:Enrofloxacin; D024841:Fluoroquinolones / Q000494:pharmacology; D005839:Gentamicins / Q000494:pharmacology; D016106:Methicillin Resistance; D010933:Plankton / Q000187:drug effects*; D013203:Staphylococcal Infections / Q000188:drug therapy / Q000382:microbiology / Q000662:veterinary*; D013210:Staphylococcus / Q000187:drug effects* / Q000502:physiology*; D014481:United States
chemical_list: D000900:Anti-Bacterial Agents; D024841:Fluoroquinolones; D005839:Gentamicins; D000077422:Enrofloxacin; D000583:Amikacin; D002437:Cefazolin