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Evaluation of the Impact of Methicillin‐Resistant Staphylococcus pseudintermedius Biofilm Formation on Antimicrobial Susceptibility
Author(s) -
Walker Meagan,
Singh Ameet,
Nazarali Alim,
Gibson Thomas W. G.,
Rousseau Joyce,
Weese J. Scott
Publication year - 2016
Publication title -
veterinary surgery
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.652
H-Index - 79
eISSN - 1532-950X
pISSN - 0161-3499
DOI - 10.1111/vsu.12535
Subject(s) - staphylococcus pseudintermedius , medicine , microbiology and biotechnology , biofilm , antimicrobial , methicillin resistant staphylococcus aureus , staphylococcus , staphylococcus aureus , bacteria , biology , genetics
Objective To compare the minimum inhibitory concentration (MIC) of four antimicrobials in planktonic vs. biofilm‐associated Staphylococcus pseudintermedius . Study Design In vitro study. Sample Population 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). Conclusion 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.