Virulence and Antifungal Susceptibility of Microsporum canis Strains from Animals and Humans

An updated list of eumycetoma causative agents and their differences in grain formation and treatment response

SUMMARYIn 2023, the World Health Organization designated eumycetoma causative agents as high-priority pathogens on its list of fungal priority pathogens. Despite this recognition, a comprehensive understanding of these causative agents is lacking, and potential variations in clinical manifestations or therapeutic responses remain unclear. In this review, 12,379 eumycetoma cases were reviewed. In total, 69 different fungal species were identified as causative agents. However, some were only identified once, and there was no supporting evidence that they were indeed present in the grain. Madurella mycetomatis was by far the most commonly reported fungal causative agent. In most studies, identification of the fungus at the species level was based on culture or histology, which was prone to misidentifications. The newly used molecular identification tools identified new causative agents. Clinically, no differences were reported in the appearance of the lesion, but variations in mycetoma grain formation and antifungal susceptibility were observed. Although attempts were made to explore the differences in clinical outcomes based on antifungal susceptibility, the lack of large clinical trials and the inclusion of surgery as standard treatment posed challenges in drawing definitive conclusions. Limited case series suggested that eumycetoma cases caused by Fusarium species were less responsive to treatment than those caused by Madurella mycetomatis. However, further research is imperative for a comprehensive understanding.

Epidemiologic features and therapeutic strategies of kerion: A nationwide multicentre study

BACKGROUND

Kerion is a severe type of tinea capitis that is difficult to treat and remains a public health problem.

OBJECTIVES

To evaluate the epidemiologic features and efficacy of different treatment schemes from real-world experience.

METHODS

From 2019 to 2021, 316 patients diagnosed with kerion at 32 tertiary Chinese hospitals were enrolled. We analysed the data of each patient, including clinical characteristics, causative pathogens, treatments and outcomes.

RESULTS

Preschool children were predominantly affected and were more likely to have zoophilic infection. The most common pathogen in China was Microsporum canis. Atopic dermatitis (AD), animal contact, endothrix infection and geophilic pathogens were linked with kerion occurrence. In terms of treatment, itraconazole was the most applied antifungal agent and reduced the time to mycological cure. A total of 22.5% of patients received systemic glucocorticoids simultaneously, which reduced the time to complete symptom relief. Furthermore, glucocorticoids combined with itraconazole had better treatment efficacy, with a higher rate and shorter time to achieving mycological cure.

CONCLUSIONS

Kerion often affects preschoolers and leads to serious sequelae, with AD, animal contact, and endothrix infection as potential risk factors. Glucocorticoids, especially those combined with itraconazole, had better treatment efficacy.

Antifungal activity of Carica papaya fruit extract against Microsporum canis: in vitro and in vivo study

Background

Tinea capitis (T. capitis), commonly known as scalp ringworm, is a fungal infection affecting the scalp and hair. Among the causative agents, Microsporum canis (M. canis) stands out, often transmitted from cats to humans (zoonotic disease). In this study, we investigated the efficacy of Carica papaya (C. papaya), fruit extract against dermatophytes, particularly M. canis, both in vitro and in vivo. Additionally, we aimed to identify the active compounds responsible for suppressing fungal growth and assess the toxicity of C. papaya on human cells.

Methodology

It conducted in two parts. First, In Vitro Study include the preparation of C. papaya fruit extract using methanol as the solvent, Phytochemical analysis of the plant extract including Gas chromatography-mass spectrometry (GC-MS) and Fourier-transform infrared spectroscopy (FTIR) was conducted, Cytotoxicity assays were performed using HUH-7 cells, employing the MTT assay (1-(3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide), Antimicrobial activity against M. canis was evaluated, including: Zone of inhibition (ZI), Minimum inhibitory concentration (MIC), Minimum fungicidal concentration (MFC), M. canis cell alterations were observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Second, In Vivo, Albino Wistar male rats were included.

Results

The phytochemical analysis of the methanolic extract from papaya revealed several functional groups, including hydroxyl, ammonia, alkane, carbonate, and alcohol. Additionally, the GC-MS analysis identified 15 compounds, with xanthosine and decanoic acid being the predominant components. The methanolic extract of papaya fruits demonstrated potent antifungal activity: ZI = 37 mm, MIC = 1,000 μg/mL, MFC = 1900 μg/mL, MTT results indicated lower cytotoxicity of the fruit extract at concentrations of 20 μg/mL, 50 μg/mL, 100 μg/mL, 150 μg/mL, and 200 μg/mL, The IC50 revealed a significant decrease in cell viability with increasing extract concentration. Notably, papaya extract induced considerable alterations in the morphology of M. canis hyphae and spores. In animal tissue, improvements were observed among the group of rats which treated with Papaya extract. This study highlights the potential of C. papaya fruits as a natural antifungal agent, warranting further exploration for clinical applications.

Remarkable Phenotypic Virulence Factors of Microsporum canis and Their Associated Genes: A Systematic Review

Microsporum canis is a widely distributed dermatophyte, which is among the main etiological agents of dermatophytosis in humans and domestic animals. This fungus invades, colonizes and nourishes itself on the keratinized tissues of the host through various virulence factors. This review will bring together the known information about the mechanisms, enzymes and their associated genes relevant to the pathogenesis processes of the fungus and will provide an overview of those virulence factors that should be better studied to establish effective methods of prevention and control of the disease. Public databases using the MeSH terms "Microsporum canis", "virulence factors" and each individual virulence factor were reviewed to enlist a series of articles, from where only original works in English and Spanish that included relevant information on the subject were selected. Out of the 147 articles obtained in the review, 46 were selected that reported virulence factors for M. canis in a period between 1988 and 2023. The rest of the articles were discarded because they did not contain information on the topic (67), some were written in different languages (3), and others were repeated in two or more databases (24) or were not original articles (7). The main virulence factors in M. canis are keratinases, fungilisins and subtilisins. However, less commonly reported are biofilms or dipeptidylpeptidases, among others, which have been little researched because they vary in expression or activity between strains and are not considered essential for the infection and survival of the fungus. Although it is known that they are truly involved in resistance, infection and metabolism, we recognize that their study could strengthen the knowledge of the pathogenesis of M. canis with the aim of achieving effective treatments, as well as the prevention and control of infection.

Fungal thermotolerance revisited and why climate change is unlikely to be supercharging pathogenic fungi (yet)

Thermotolerance has been viewed as an uncommon characteristic among the fungi and one of the reasons that less than 1% of the described species operate as opportunistic pathogens of humans. Growth at 37°C is certainly a requirement for a fungus that invades the body core, but tens of thousands of nonpathogenic species are also able to grow at this temperature. Ergo, body temperature does not serve as a thermal barrier to the development of infections by many harmless fungi. The absence of other virulence factors must be more demanding. This observation raises questions about the hypothetical links between climate change and the increasing number of life-threatening human mycoses. Given the widespread distribution of fungal thermotolerance and the 1°C (2°F) increase in global temperature over the last 140 years it seems unlikely that the warming climate has driven the evolution of more virulent strains of fungi. More compelling explanations for the changes in the behavior of fungi as disease agents include their adaptation to the widening use of azole antifungals in hospitals and the wholesale application of millions of tons of the same class of heterocyclic chemicals in agriculture. On the other hand, climate change is having a significant effect on the spread of human mycoses by extending the geographical range of pathogenic fungi. A related increase in fungal asthma caused by spore inhalation is another likely consequence of planetary change.

In vitro virulotyping, antifungal susceptibility testing and DNA fingerprinting of Microsporum canis strains of canine and feline origin

Microsporum canis is considered the common dermatophyte agent associated with ringworm in felines and canines. In the present study, we sampled n = 548 felines and canines for the probable isolation of M. canis. The rate of isolation from the cats and dogs was 70.27 % (52/74) and 1.68 % (8/474), respectively and Persian cats were found to be highly susceptible to M. canis infection. The strains were evaluated for their production of phospholipase, lipase, catalase, and hemolysis and their ability to grow at 35 ℃. All the strains were identified as low producers of catalase and n = 17 strains exhibited high thermotolerance ability. Terbinafine was found to be the most effective antifungal drug and fluconazole was the least effective, in vitro. AFLP analysis revealed three genotypes of M. canis with 15 sub-clusters showing ≥ 90 % similarity and 7 sub-clusters exhibiting 100 % similarity. However, the phenotypic characters cannot be attributed based on the AFLP profiles.

Antifungal Activity of N-Arylbenzoquinaldinium Derivatives against a Clinical Strain of M. canis

Background

Microsporum canis (Bodin, 1902) is a dermatophyte, which is widely represented in the developing and the developed world alike. Commonly transmitted from domestic animals it is particularly dangerous for immunosuppressed patients due to AIDS, cancer or transplant surgery. Search for new perspective antimycotic derivatives becomes an urgent task in the disease containment. Previously, several quinolinium analogs were screened for their antibacterial activity (E. coli, St. aurous) by our research team. Furthermore, some N-phenylbenzoquinaldinium derivatives have shown antifungal activity against Candida albicans and Candida krusei.

Aims

In this study, we sought to investigate fungicidal properties of N-arylbenzoquinaldinium derivatives against a clinical strain of Microsporum canis for future medicinal applications.

Materials and Methods

N-phenyl-[f]-benzoquinaldinium salts were prepared by a variation of the previously described technique and tested against a clinical strain of the fungus of Microsporum canis 114 harvested from pathogenic material of a patient (Perm, Russia, 2014).

Results

N-phenyl-[f]-benzoquinaldinium tetrafluoroborate has shown antifungal activity par to (or exceeding) that of commercially available medication. Moreover, this benzoquinaldinium analog can be potentially labelled with tritium by our nuclear-chemical method, making it amenable for the sensitive pharmacokinetic studies.

Conclusions

N-phenyl-[f]-benzoquinaldinium tetrafluoroborate has been shown as a promising compound for the further development of potent antifungal agents as well as radiotracers for further elucidation of biological pathways of antifungal activity.

Comparison of virulence factors and susceptibility profiles of Malassezia furfur from pityriasis versicolor patients and bloodstream infections of preterm infants

In spite of the increasing medical interest in Malassezia yeasts, the virulence factors of Malassezia furfur causing bloodstream infections (BSI) were never investigated. Therefore, phospholipase (Pz), lipase (Lz), hemolysin (Hz), biofilm production, and in vitro antifungal susceptibility profiles were evaluated in M. furfur strains, isolated from both pityriasis versicolor (PV) patients (n = 18; Group 1) or from preterm infants BSI (n = 21; Group 2). All the test stains exhibited Pz activity, whereas 92.3% and 97.4% of strains exhibited Lz and Hz activities, respectively. Pz, Lz, and Hz activities were higher (i.e., lower values) within Group 1 strains (i.e., 0.48, 0.40, and 0.77) than those within Group 2 (i.e., 0.54, 0.54, and 0.81). The biofilm production was higher within Malassezia isolates from Group 2 (0.95 ± 0.3) than from Group 1 (0.72 ± 0.4). Itraconazole and posaconazole were the most active drugs against M. furfur, followed by amphotericin B and fluconazole. The minimum inhibitory concentrations (MIC) values varied according to the origin of M. furfur strains being statistically lower in M. furfur from Group 1 than from Group 2. This study suggests that M. furfur strains produce hydrolytic enzymes and biofilm when causing PV and BSI. Data show that the phospholipase activity, biofilm production, and a reduced antifungal susceptibility profile might favor M. furfur BSI, whereas lipase and hemolytic activities might display a synergic role in skin infection.

Virulence factors of Malassezia strains isolated from pityriasis versicolor patients and healthy individuals

Over the last decade, Malassezia species have emerged as increasingly important pathogens associated with a wide range of dermatological disorders and bloodstream infections. The pathogenesis of Malassezia yeasts is not completely clear but it seems to be strictly related to Malassezia strains and hosts and need to be better investigated. This study aimed to assess the enzymatic activities, biofilm formation and in vitro antifungal profiles of Malassezia spp. from Pityriasis versicolor and heathy patients. The potential relationship between virulence attributes, the antifungal profiles and the origin of strains were also assessed. A total of 44 Malassezia strains isolated from patients with (n = 31) and without (n = 13) Pityriasis versicolor (PV) were employed to evaluate phospholipase (Pz), lipase (Lz), hemolytic (Hz) activities and biofilm formation. In addition, in vitro antifungal susceptibility testing was conducted using the CLSI broth microdilution with some modifications. A high percentage of strains produced phospholipase, lipase, hemolysins and biofilm regardless of their clinical origin. The highest number of strains producing high enzymatic activities came from PV patients. A correlation between the intensity of hydrolytic activities (lipase and phospholipase activities) and the hemolytic activity was detected. Positive associations between Lz and the low fluconazole susceptibility and Hz and biofilm formation were observed. These results suggest that enzyme patterns and biofilm formation together with antifungal profiles play a role in the pathogenicity of Malassezia spp. and might explain the implication of some Malassezia spp. in invasive fungal infections and in the development of inflammation.

Evaluation of Short-Chain Antimicrobial Peptides With Combined Antimicrobial and Anti-inflammatory Bioactivities for the Treatment of Zoonotic Skin Pathogens From Canines

The incidence of zoonotic Staphylococcus pseudintermedius and Microsporum canis infections is rapidly growing worldwide in the context of an increasing frequency of close contact between animals and humans, presenting challenges in both human and veterinary medicine. Moreover, the development of microbial resistance and emergence of recalcitrant biofilms, accompanied by the insufficiency of new antimicrobial agents, have become major obstacles in treating superficial skin infections caused by various microbes including S. pseudintermedius and M. canis. Over recent years, the prospects of antimicrobial peptides as emerging antimicrobials to combat microbial infections have been demonstrated. In our study, two novel short-chain peptides, namely, allomyrinasin and andricin B, produced by Allomyrina dichotoma and Andrias davidianus, were revealed to exhibit potent antimicrobial efficacy against clinical isolates of S. pseudintermedius and M. canis with remarkable and rapid fungicidal and bactericidal effects, while allomyrinasin exhibited inhibition of biofilm formation and eradication of mature biofilm. These peptides displayed synergistic activity when combined with amoxicillin and terbinafine against S. pseudintermedius and M. canis. Cytoplasmic leakage via cytomembrane permeabilization serves as a mechanism of action. Extremely low hemolytic activity and serum stability in vitro, as well as superior anti-infective efficacy in reducing bacterial counts and relieving the inflammatory response in vivo, were detected. The potent antibacterial, antifungal, and anti-inflammatory activities of allomyrinasin and andricin B might indicate promising anti-infective alternatives for the treatment of S. pseudintermedius and M. canis infections in the context of human and veterinary medicine.