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Antibacterial effect of N ‐acetylcysteine in combination with antimicrobials on common canine otitis externa bacterial isolates
Author(s) -
May Elizabeth R.,
Ratliff Brette E.,
Bemis David A.
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.12795
Subject(s) - staphylococcus pseudintermedius , enrofloxacin , gentamicin , microbiology and biotechnology , antimicrobial , otitis , antibiotics , agar plate , medicine , biology , bacteria , staphylococcus aureus , staphylococcus , ciprofloxacin , surgery , genetics
Background Approved treatments for canine otitis externa are limited in variety and may contain ototoxic ingredients. With bacterial resistance an ongoing concern, it would be ideal if non‐ototoxic agents combined with antibiotics resulted in a synergistic effect, requiring lower antibiotic concentrations to treat infections. Evidence of synergism and antagonism between N ‐acetylcysteine ( NAC ) and various antibiotic classes has been reported; the present research group was interested in examining these interactions. Hypothesis/Objectives To determine if NAC , an otoprotective and antimicrobial compound, has synergistic activity when combined with enrofloxacin or gentamicin in vitro against bacterial isolates causing canine otitis externa. Animals Twenty‐two isolates from canine clinical cases of otitis externa were identified and tested, including seven Staphylococcus pseudintermedius , 12 Pseudomonas aeruginosa and three Corynebacterium spp. isolates. Methods and materials Each isolate was grown on blood agar for 24 h and transferred to Mueller–Hinton broth ( MHB ), with a final concentration of 5 × 10 5 cfu / mL . Each well was inoculated with 50 μL of bacterial suspension. N ‐acetylcysteine was diluted in MHB to a starting concentration of 160 mg/ mL . Enrofloxacin and gentamicin were diluted to 64 μg/ mL . Individual and checkerboard serial microdilution assays were performed in triplicate with negative controls for all isolates tested. Results Interactions observed for NAC and enrofloxacin were synergistic (4.5%), indifferent (77.3%) or antagonistic (18.2%). Interactions observed for NAC and gentamicin were synergistic (4.5%), indifferent (45.5%) or antagonistic (50%). Conclusions and Clinical relevance Most interactions between NAC and enrofloxacin or gentamicin were indifferent or antagonistic at the concentrations tested in vitro .