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Background <p><i>Staphylococcus pseudintermedius</i> is a natural component of the normal microbiota of the skin and mucous membranes of dogs. However, it can also act as a causative agent of pyoderma and <i>otitis externa</i>. The emergence of multidrug-resistant strains of this staphylococcus has prompted the search for new antimicrobial agents. The so-called “Thieves” blend, a relatively little-known mixture of essential oils, is based on a medieval recipe and comprises the following essential oils (EOs): cinnamon, clove, rosemary, eucalyptus, and lemon. The aim of this study was to evaluate the antimicrobial activity of this medieval blend against <i>S. pseudintermedius</i> as a potential alternative to antibiotics in the treatment of canine <i>otitis externa</i>.</p> Results <p>The antimicrobial activity of the blend was tested against a total of 18 staphylococcal isolates obtained from clinical cases of canine <i>otitis externa</i> and two reference strains of <i>S. pseudintermedius</i>. In total, 16 potential antimicrobial agents were evaluated, including five commercial single EOs present in the blend, one commercial Nature’s Shield™ blend, six blends formulated for this study, and four chemical compounds representative of essential oil chemotypes (cinnamaldehyde, eugenol, 1,8-cineole, and <i>d</i>-limonene). Antimicrobial activity against <i>S. pseudintermedius</i> was determined using the minimum inhibitory concentration (MIC) method. The time and rate of action of the EOs at effective concentrations were also assessed by time–kill analysis. The most effective oils were those in the cinnamon-like group (MIC, 0.25–0.69% v/v) and the clove-like group (MIC, approximately 1% v/v). All other blends also showed satisfactory activity (MIC, 1–2% v/v). Regardless of the strain’s level of antibiotic resistance, almost all tested antimicrobials from the above groups completely killed the tested staphylococci within 30&#xa0;min. Low antibacterial activity was observed for oils containing high amounts of 1,8-cineole and <i>d</i>-limonene. Among these, eucalyptus EO showed the highest activity (MIC, 2–4% v/v; complete elimination of staphylococci in approximately 2&#xa0;h), whereas the remaining agents exhibited high MIC values and slow bactericidal activity (MIC, 4–8% v/v; 8–24&#xa0;h).</p> Conclusions <p>Owing to their complex chemical composition, Thieves-type blends show strong in vitro potential against <i>Staphylococcus pseudintermedius</i>, most likely due to their high content of cinnamon and clove EOs, which were the most effective agents in this study. Further studies are required; however, these preliminary findings suggest that, in the future, it may be possible to reduce antibiotic use in the treatment of canine <i>otitis externa</i> by using medicinal products containing essential oils as alternatives.</p>

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Activity of thieves-type protective blends and their individual components (cinnamon, clove, rosemary, eucalyptus and lemon essential oils) against Staphylococcus pseudintermedius strains isolated from canine otitis externa

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年5月25日

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  • Małgorzata Anna Szewczuk,
  • Sławomir Zych,
  • Tomasz Stankiewicz,
  • Barbara Błaszczyk,
  • Ireneusz Ochmian

摘要

Background

Staphylococcus pseudintermedius is a natural component of the normal microbiota of the skin and mucous membranes of dogs. However, it can also act as a causative agent of pyoderma and otitis externa. The emergence of multidrug-resistant strains of this staphylococcus has prompted the search for new antimicrobial agents. The so-called “Thieves” blend, a relatively little-known mixture of essential oils, is based on a medieval recipe and comprises the following essential oils (EOs): cinnamon, clove, rosemary, eucalyptus, and lemon. The aim of this study was to evaluate the antimicrobial activity of this medieval blend against S. pseudintermedius as a potential alternative to antibiotics in the treatment of canine otitis externa.

Results

The antimicrobial activity of the blend was tested against a total of 18 staphylococcal isolates obtained from clinical cases of canine otitis externa and two reference strains of S. pseudintermedius. In total, 16 potential antimicrobial agents were evaluated, including five commercial single EOs present in the blend, one commercial Nature’s Shield™ blend, six blends formulated for this study, and four chemical compounds representative of essential oil chemotypes (cinnamaldehyde, eugenol, 1,8-cineole, and d-limonene). Antimicrobial activity against S. pseudintermedius was determined using the minimum inhibitory concentration (MIC) method. The time and rate of action of the EOs at effective concentrations were also assessed by time–kill analysis. The most effective oils were those in the cinnamon-like group (MIC, 0.25–0.69% v/v) and the clove-like group (MIC, approximately 1% v/v). All other blends also showed satisfactory activity (MIC, 1–2% v/v). Regardless of the strain’s level of antibiotic resistance, almost all tested antimicrobials from the above groups completely killed the tested staphylococci within 30 min. Low antibacterial activity was observed for oils containing high amounts of 1,8-cineole and d-limonene. Among these, eucalyptus EO showed the highest activity (MIC, 2–4% v/v; complete elimination of staphylococci in approximately 2 h), whereas the remaining agents exhibited high MIC values and slow bactericidal activity (MIC, 4–8% v/v; 8–24 h).

Conclusions

Owing to their complex chemical composition, Thieves-type blends show strong in vitro potential against Staphylococcus pseudintermedius, most likely due to their high content of cinnamon and clove EOs, which were the most effective agents in this study. Further studies are required; however, these preliminary findings suggest that, in the future, it may be possible to reduce antibiotic use in the treatment of canine otitis externa by using medicinal products containing essential oils as alternatives.