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Interaction of chlorhexidine with tris EDTA or miconazole in vitro against canine meticillin‐resistant and ‐susceptible Staphylococcus pseudintermedius isolates from two UK regions
Author(s) -
Clark SiânMarie,
Loeffler Anette,
Schmidt Vanessa M,
Chang YuMei,
Wilson Alison,
Timofte Dorina,
Bond Ross
Publication year - 2016
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.12357
Subject(s) - miconazole , chlorhexidine , staphylococcus pseudintermedius , microbiology and biotechnology , tris , minimum inhibitory concentration , antimicrobial , chemistry , staphylococcus aureus , medicine , staphylococcus , biology , bacteria , biochemistry , dentistry , antifungal , genetics
Background Topical therapy is an important alternative to systemic antibacterial therapy for treatment of canine superficial pyoderma in light of the emergence of multidrug‐resistant staphylococci. Chlorhexidine is widely used in shampoo products alone or in combination with miconazole or tromethamine‐ethylenediaminetetraacetic acid (tris EDTA ). Comparisons of these combinations have not been made. Hypothesis/Objectives To determine minimum inhibitory concentrations ( MIC s) of combinations of chlorhexidine/miconazole and chlorhexidine/tris EDTA in vitro in a collection of Staphylococcus pseudintermedius ( SP ) from northern ( NUK ) and southeastern ( SEUK ) United Kingdom ( UK ) sources. Methods MIC s of chlorhexidine, miconazole, tris EDTA and combinations of chlorhexidine/miconazole (1:1) or chlorhexidine/tris EDTA (80:16:1 and 80:5:1) were determined for 196 canine SP isolates from NUK [49 meticillin‐resistant ( MRSP ), 50 meticillin‐susceptible ( MSSP )] and fom SEUK (48 MRSP , 49 MSSP ) using agar dilution. Results Tris EDTA alone did not inhibit growth. Chlorhexidine/miconazole MIC s (median = 0.5 mg/L) were lower than those of either drug alone ( P < 0.05) and lower than chlorhexidine/tris EDTA MIC s (median = 1 mg/L; P < 0.0005) in each bacterial type and from both regions, except for miconazole in NUK MSSP . An additive interaction was noted between chlorhexidine and miconazole or tris EDTA (80:16:1 ratio) in 79 and 43 isolates, respectively, whereas antagonism between chlorhexidine and tris EDTA was noted for three isolates. NUK isolates were more susceptible than SEUK isolates ( P < 0.05), except MRSP exposed to chlorhexidine and the chlorhexidine/tris EDTA (80:16:1) combination. Conclusions and Clinical Importance These low MIC s are likely to be exceeded by topical therapy. Evaluation of the mechanisms by which chlorhexidine combinations interact to reduce MIC s is warranted, in view of increasing concerns of biocide tolerance in staphylococci.