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Antibacterial effect of N-acetylcysteine in combination with antimicrobials on common canine otitis externa bacterial isolates.
Vet Dermatol. 2019 Dec; 30(6):531-e161.VD

Abstract

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 × 105 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.

Authors+Show Affiliations

Department of Small Animal Clinical Sciences, University of Tennessee, 2407 River Drive, Knoxville, TN, 37996, USA.Department of Small Animal Clinical Sciences, University of Tennessee, 2407 River Drive, Knoxville, TN, 37996, USA.Department of Biomedical and Diagnostic Sciences, University of Tennessee, 2407 River Drive, Knoxville, TN, 37996, USA.

Pub Type(s)

Journal Article

Language

eng

PubMed ID

31670428

Citation

May, Elizabeth R., et al. "Antibacterial Effect of N-acetylcysteine in Combination With Antimicrobials On Common Canine Otitis Externa Bacterial Isolates." Veterinary Dermatology, vol. 30, no. 6, 2019, pp. 531-e161.
May ER, Ratliff BE, Bemis DA. Antibacterial effect of N-acetylcysteine in combination with antimicrobials on common canine otitis externa bacterial isolates. Vet Dermatol. 2019;30(6):531-e161.
May, E. R., Ratliff, B. E., & Bemis, D. A. (2019). Antibacterial effect of N-acetylcysteine in combination with antimicrobials on common canine otitis externa bacterial isolates. Veterinary Dermatology, 30(6), 531-e161. https://doi.org/10.1111/vde.12795
May ER, Ratliff BE, Bemis DA. Antibacterial Effect of N-acetylcysteine in Combination With Antimicrobials On Common Canine Otitis Externa Bacterial Isolates. Vet Dermatol. 2019;30(6):531-e161. PubMed PMID: 31670428.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Antibacterial effect of N-acetylcysteine in combination with antimicrobials on common canine otitis externa bacterial isolates. AU - May,Elizabeth R, AU - Ratliff,Brette E, AU - Bemis,David A, Y1 - 2019/10/31/ PY - 2019/08/12/accepted PY - 2019/11/2/pubmed PY - 2020/4/10/medline PY - 2019/11/1/entrez SP - 531 EP - e161 JF - Veterinary dermatology JO - Vet. Dermatol. VL - 30 IS - 6 N2 - 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 × 105 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. SN - 1365-3164 UR - https://www.unboundmedicine.com/medline/citation/31670428/Antibacterial_effect_of_N_acetylcysteine_in_combination_with_antimicrobials_on_common_canine_otitis_externa_bacterial_isolates_ L2 - https://doi.org/10.1111/vde.12795 DB - PRIME DP - Unbound Medicine ER -