Antifungal in vitro Activity of Essential Oils against Clinical Isolates of <b><i>Malassezia pachydermatis</i></b> from Canine Ears: A Report from a Practice Laboratory

Abstract

Background: The yeast Malassezia pachydermatis is a commensal but also the most isolated pathogenic yeast in canine otitis externa. Essential oils (EOs) exhibit antimicrobial activity and thus could be an alternative for treatment of otitis. Objective: The aim of this study was to analyse the in vitro efficacy of EOs against M. pachydermatis isolates from canine ears. Materials and Methods: Twenty-two EOs were tested for their in vitro activity against 15 M. pachydermatis isolates by agar disc diffusion. In addition, diluted EOs were tested and volatile antifungal activity was analysed by vapour assay. Results: Most EOs showed in vitro efficacy against M. pachydermatis. A different susceptibility pattern of tested isolates was found. Overall, the most potential EO was lemon grass. Also, cinnamon leaf, clove, manuka, Indian melissa, oregano, palmarosa, and winter savory oil exhibited a strong antifungal activity. Volatile activity was proven by the inhibiting effect in vapour assay. Conclusion: EOs show in vitro activity against M. pachydermatis. This study gives scientific background for the use of EOs in veterinary medicine. Diverse susceptibility patterns of different M. pachydermatis strains emphasise the helpfulness of an aromatogram as one lead for the best choice of an EO for therapy. Antimykotische In-vitro-Wirksamkeit ätherischerÖle gegen Malassezia pachydermatis isoliert aus Hundeohren: Ein Bericht aus dem Routinelabor Schlüsselwörter Ätherische Öle · Malassezia pachydermatis · Otitis externa · Veterinärmedizin Zusammenfassung Einleitung: Der Hefepilz Malassezia pachydermatis gilt als Kommensale, ist aber gleichzeitig auch der am häufigsten isolierte Hefepilz bei caniner Otitis externa. Ätherische Öle könnten aufgrund ihrer antimikrobiellen Eigenschaften als alternative Therapie der Otitis verwendet werden. Zielsetzung: Ziel dieser Studie war die Untersuchung der antifungalen In-vitro-Wirksamkeit ätherischer Öle gegen M. pachydermatis-Isolate aus Hundeohren. Material und Methoden: Die In-vitro-Aktivität von 22 ätherischen Ölen wurde mittels Agar-Plättchen-Diffusionstest gegen 15 M. pachydermatis-Isolate untersucht. Zusätzlich wurden Verdünnungen der ätherischen Öle getestet und die volatile Wirkung mittels "vapour assay" analysiert. Ergebnisse: Die meisten ätherischen Öle zeigten in vitro eine Wirksamkeit gegen M. pachydermatis. Es konnte eine unterschiedliche Empfindlichkeit einzelner M. pachydermatis-Isolate gefunden werden. Lemongrasöl erwies sich als das po-tenteste ätherische Öl. Ebenfalls zeigten Zimtblätter-, Nelken-, Manuka-, indisches Melissen-, Oregano-, Palmarosa-und Bergbohnenkrautöl eine starke antifungale Wirksamkeit. Die volatile Wirkung konnte mittels "vapour assay" gezeigt werden. Schlussfolgerung: In vitro zeigen ätherische Öle eine Wirksamkeit gegen den Hefepilz M. pachydermatis. Diese Studie bietet eine wissenschaftliche Basis zur Anwendung ätherischer Öle in der Veterinärmedizin. Die unterschiedliche Empfindlichkeit der verschiedenen M. pachydermatis-Isolate gegenüber einzelner äther...

Antimicrobial Activity of Essential Oils against Staphylococcus and Malassezia Strains Isolated from Canine Dermatitis

“…Another interesting feature is the high sensitivity of Malassezia to C. zeylanicum. These results are in agreement with findings reported by Bismarck et al [52] and Sim et al [56] in otologic canine isolates. This EO, in fact, although poorly effective against molds such as A. fumigatus [49] and dermatophytes [55], showed a strong antimicrobial activity versus Salmonella enterica serotype Typhimurium and Escherichia coli isolated from poultry [50].…”

“…This finding is of interest, considering that this EO also appeared active against staphylococci. S. montana has been recently reported as active against M. pachydermatis recovered from canine otitis [52], Candida albicans [53], and Candida glabrata [54] and moderately effective against dermatophytes [55], suggesting a good activity against yeasts.…”

“…On the other hand, Malassezia yeasts showed a marked variability in their sensitivity to EOs. For these reasons, a sensitivity assay of the fungal isolates is recommended, as suggested by Bismarck et al [52].…”

Malassezia Yeasts in Veterinary Dermatology: An Updated Overview

“…There are reports of in vitro efficacy against M. pachydermatis of a honey-based gel (Oliveira et al, 2018), monensin and, to a lesser extent, narasin (polyether ionophores originally marketed as anticoccidials and growth-promoting modifiers of the bovine rumen flora; Chan et al, 2018Chan et al, , 2019. Multiple recent publications have explored the potential antifungal utility of essential oils, complex mixtures of highly concentrated aromatic oils (primarily terpenes and/or phenylpropanoids) extracted from plants by steam distillation, hydrodiffusion or pressure (Manion and Widder, 2017;Bismark et al, 2019). A previous randomized clinical trial reported persistent efficacy of a commercial essential oil product (Malacalm, Flora Slr Oli essenziali, Lorenzana, Italy) applied twice daily for 1 month to dogs with Malassezia dermatitis (Nardoni et al, 2014), although the study is weakened by incomplete data on randomization and clinical scores (Bond et al, 2020).…”

“…Most of the recent studies have been conducted in vitro and their utility in clinical practice remains largely untested. Comparisons between studies are hampered by an absence of agreed standard testing methods that are not yet optimized, arbitrary assignment of interpretative criteria, and likely batch variation in activities of essential oils prepared by different methods (Bismark et al, 2019). 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).…”