Antimicrobial activity of thyme oil, oregano oil, thymol and carvacrol against sensitive and resistant microbial isolates from dogs with otitis externa

Abstract

Background -Multidrug-resistant pathogens present a major global challenge in antimicrobial therapy and frequently complicate otitis externa in dogs.Hypothesis/Objectives -In vitro efficacy of oregano oil, thyme oil and their main phenolic constituents against bacterial and fungal isolates associated with canine otitis externa were investigated. It was hypothesized that the main phenolic components would have greater antimicrobial activity compared to the relative essential oil.Methods and materials -Antimicrobial susceptibility testing was performed using broth microdilution with spot-plating technique to determine minimum inhibitory and bactericidal/fungicidal concentrations (MICs, MBCs and MFCs). A time-kill kinetics assay was performed to confirm the bactericidal and fungicidal activity of the oils and their phenolic constituents. One hundred bacterial and fungal isolates, including meticillin-susceptible Staphylococcus pseudintermedius (n = 10), meticillin-resistant S. pseudintermedius (n = 10), b-haemolytic Streptococcus spp. (n = 20), Pseudomonas aeruginosa (n = 20; including 10 isolates resistant to one or two antimicrobials), Proteus mirabilis (n = 20) and Malassezia pachydermatis (n = 20) from dogs with otitis externa were used.Results -Oregano oil, thyme oil, carvacrol and thymol exhibited antibacterial activity against all bacterial and fungal isolates tested. MIC 90 values ranged from 0.015 to 0.03% (146-292 lg/mL) for the Gram-positive bacteria and P. mirabilis. For P. aeruginosa and M. pachydermatis, MIC 90 values ranged from 0.09 to 0.25% (800-2,292 lg/mL).Conclusions and clinical significance -Oregano oil, thyme oil, carvacrol and thymol showed good in vitro bactericidal and fungicidal activity against 100 isolates from dogs with otitis externa, including some highly drug-resistant isolates. These essential oils and their main phenolic constituents have the potential to be further investigated in vivo for the treatment of canine otitis externa.

Malassezia Yeasts in Veterinary Dermatology: An Updated Overview

“…Recently, anti-Malassezia effects have been observed in vitro using winter savory, lemon grass, oregano, palmarosa and cinnamon leaf oils by agar disc diffusion and vapor assays (Bismark et al, 2019). Oregano oil and thyme oil and their major phenolic components (carvacrol, thymol) were fungicidal against M. pachydermatis when tested using agar dilution (Sim et al, 2019). There are recent reports of synergistic interactions between essential oil components and azoles or nystatin against M. pachydermatis, including carvacrol and miconazole or nystatin, thymol and nystatin (Schlemmer et al, 2019b), and between clotrimazole and essential oils of Melaleuca alternifolia, Mentha piperita, and Origanum vulgare (Bohmova et al, 2019).…”

Antibody levels to Malassezia pachydermatis and Staphylococcus pseudintermedius in atopic dogs and their relationship with lesion scores

“…1 All atopic dogs had suffered from recurrent infections with M. pachydermatis and/or S. pseudintermedius, based on cytological findings. [14][15][16] Cutaneous adverse food reaction was ruled out by elimination diet for a minimum of eight weeks. After successful treatment with antimicrobial therapy and two weeks withdrawal of anti-inflammatory, antipruritic and antimicrobial drugs (none of the dogs had been treated with steroids), 17 intradermal testing (IDT) with environmental allergens was performed according to previous reports.…”

Pseudomonas aeruginosa en la otitis externa canina: situación actual

“…Estos resultan ser el producto final del metabolismo secundario de plantas aromáticas y se conforman fundamentalmente de terpenos con actividad y composición variada de entre 20 y 60 compuestos (Buldain et al, 2017(Buldain et al, , 2018. Recientemente, Sim et al (2019) reportaron los resultados obtenidos en estudios cuantitativos de sensibilidad in vitro (concentración bactericida mínima, concentración inhibitoria mínima y curvas de muerte bacteriana) evaluando la eficacia de aceites esenciales de orégano, tomillo y sus principales componentes fenólicos (carvacrol y timol), frente a diversos patógenos multirresistentes como S. pseudinter medius meticilinoresistente y P. aeruginosa aislados a partir de pacientes caninos con OE. Los aceites evaluados, el carvacrol y el timol exhibie ron actividad antibacteriana contra todos los aisla mientos estudiados, resultando prometedor conti nuar con dicha investigación, ya que aún no existen datos de pruebas realizadas in vivo.…”