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In vitro antimicrobial activity of topical otological antimicrobials and Tris‐ EDTA against resistant Staphylococcus pseudintermedius and Pseudomonas aeruginosa isolates from dogs
Author(s) -
Boyd Megan,
Santoro Domenico,
Gram Dunbar
Publication year - 2019
Publication title -
veterinary dermatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.744
H-Index - 60
eISSN - 1365-3164
pISSN - 0959-4493
DOI - 10.1111/vde.12717
Subject(s) - staphylococcus pseudintermedius , pseudomonas aeruginosa , antimicrobial , microbiology and biotechnology , in vitro , tris , staphylococcus aureus , staphylococcus intermedius , staphylococcus , medicine , chemistry , biology , bacteria , biochemistry , genetics
Background The value of susceptibility tests for the selection of topical otological antimicrobial agents is unclear. Laboratories test antibiotic concentrations substantially lower than concentrations supplied in topical formulations. Additionally, microbiological consensus statements are not available for topical antimicrobials. Hypothesis/Objectives The primary aim of this study was to measure the minimum inhibitory and bactericidal concentrations of enrofloxacin, gentamicin, marbofloxacin, neomycin, orbifloxacin, polymyxin B and silver sulfadiazine from concentrations available in otological formulations ( COF ) to 1:59,000 dilution. The secondary aim was to evaluate the effect of Tris‐ EDTA in conjunction with these antimicrobial agents. Methods and materials Twenty resistant clinical isolates [ Staphylococcus pseudintermedius (n = 10) and Pseudomonas aeruginosa (n = 10)] were tested by broth microdilution using a concentrated inoculum (3.75 × 10 7 cfu/mL). Results Concentrations available in otological formulations were at least 26× greater than the MIC s for S . pseudintermedius and P. aeruginosa . COF s of polymyxin B and SSD were 27× greater than the MBC s for P. aeruginosa , whereas all other antimicrobial COF s were equal to or less than the MBC s for both organisms. Tris‐ EDTA significantly reduced the MIC s of all antimicrobials, except with SSD for P. aeruginosa , and it significantly increased the MIC of SSD for S. pseudintermedius . Conclusions and clinical importance Further studies are warranted to validate the present results in vivo . COF s are inhibitory and less likely bactericidal, with few exceptions, against resistant strains of these organisms. Tris‐ EDTA may be advantageous for P. aeruginosa whereas no additional benefit is afforded against S. pseudintermedius . Susceptibility tests may not be useful for the selection of topical otological antimicrobial agents.