Microsporum canis Antifungal Susceptibility and Therapy: A Review Original paper
Researched by:
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Karen Pendergrass
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Karen Pendergrass
Karen Pendergrass is a microbiome researcher specializing in microbiome-targeted interventions (MBTIs). She systematically analyzes scientific literature to identify microbial patterns, develop hypotheses, and validate interventions. As the founder of the Microbiome Signatures Database, she bridges microbiome research with clinical practice. In 2012, based on her own investigative research, she became the first documented case of FMT for Celiac Disease—four years before the first published case study.
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Microbes
Microbes
Microbes, short for microorganisms, are tiny living organisms that are ubiquitous in the environment, including on and inside the human body. They play a crucial role in human health and disease, functioning within complex ecosystems in various parts of the body, such as the skin, mouth, gut, and respiratory tract. The human microbiome, which is […]
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Microsporum canis (M. canis)
Microsporum canis (M. canis)
OverviewMicrosporum canis (M. canis) is a zoophilic dermatophyte common in cats and dogs, responsible for 90% of feline dermatophytoses worldwide.[1][2] It has significant zoonotic potential, transmitting to humans through fomites or direct animal contact, causing severe superficial mycosis. M. canis is considered anthropo-zoophilic and can infect pediatric or immunocompromised patients, causing severe inflammatory responses such […]
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Karen Pendergrass
Researched by:
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Karen Pendergrass
ID
Karen Pendergrass
Microbiome Signatures identifies and validates condition-specific microbiome shifts and interventions to accelerate clinical translation. Our multidisciplinary team supports clinicians, researchers, and innovators in turning microbiome science into actionable medicine.
Karen Pendergrass
What was reviewed?
This review article assessed the antifungal therapy options and susceptibility profiles of Microsporum canis (M. canis), a zoophilic dermatophyte responsible for dermatophytosis in animals and humans. The paper provided an in-depth analysis of conventional antifungal treatments and in vitro susceptibility data obtained using broth microdilution (CLSI-based), E-test, and disk diffusion methods. It emphasized the lack of standardized susceptibility testing protocols for M. canis and the implications this variability has on clinical decision-making and the interpretation of minimum inhibitory concentrations (MICs).
Who was reviewed?
The review synthesized findings from studies involving both human and animal M. canisinfections. It compiled clinical trial data from domestic cats, in vivo veterinary studies, and in vitro susceptibility studies of fungal isolates collected globally. The included literature encompassed dermatophyte strains tested under variable laboratory conditions, particularly those from cases of recalcitrant or treatment-resistant dermatophytosis.
Most important findings
M. canis exhibits substantial variability in antifungal susceptibility depending on the methodology employed for testing, which significantly influences therapeutic outcomes and drug efficacy interpretation. Terbinafine (TER) and itraconazole (ITZ) consistently demonstrated superior in vivo and in vitro efficacy when compared to fluconazole (FLZ) and griseofulvin (GRI), with TER and ITZ associated with faster healing times and lower minimum inhibitory concentrations (MICs). However, treatment failures have been reported in 25–40% of patients, frequently attributed to factors such as variability in MIC results, suboptimal drug penetration into infected tissues, poor patient compliance, and the emergence of antifungal resistance.
Notably, methodological disparities across susceptibility assays—including broth microdilution, E-test, and disk diffusion—have been shown to introduce significant variability. Key parameters such as inoculum size (ranging from 10³ to 10⁶ CFU/mL), culture medium (e.g., PDA versus RPMI), incubation temperature and duration, and endpoint criteria (e.g., MIC-50, MIC-80, or MIC-0) critically affect the resulting MIC values, thereby complicating cross-study comparisons and hindering the development of standardized clinical breakpoints.
| Antifungal Agent | In Vitro Activity Consistency | Notable Findings |
|---|---|---|
| Terbinafine (TER) | High | Most effective in in vivo feline models and showed high inhibition zones (DD method). A TER-resistant strain has been reported. |
| Itraconazole (ITZ) | High | Quick healing and low MICs across methods; preferred over GRI. |
| Fluconazole (FLZ) | Low | Consistently poor activity, with high MICs and poor zone inhibition across all methods. |
| Griseofulvin (GRI) | Moderate to Low | Inferior to ITZ and TER in both speed and consistency; associated with therapeutic failure. |
| Voriconazole (VOR) | Limited Data | Promising based on DD zone inhibition but underexplored. |
Key implications
The absence of a standardized, validated antifungal susceptibility method for M. canis undermines accurate resistance profiling and therapy optimization. The variability in MICs depending on technical parameters highlights the urgent need for harmonized protocols, particularly for dermatophyte infections. Moreover, the low efficacy of FLZ and emerging resistance to TER suggest a potential therapeutic shift toward ITZ as a first-line systemic antifungal. Given the zoonotic potential of M. canis and increasing recalcitrance, routine susceptibility testing using standardized CLSI protocols should be adopted in both clinical and veterinary settings to ensure appropriate antifungal stewardship and reduce transmission risks.