Assessment of the subtilisin genes in Trichophyton rubrum and Microsporum canis from dermatophytosis

Review on host-pathogen interaction in dermatophyte infections

Dermatophytosis is a common superficial fungal infection of the skin and its appendages caused by dermatophytes. Recent times have witnessed a dynamic evolution of dermatophytes driven by their ecology, reproduction, pathogenicity and host immune response, influenced by population migration and socioeconomic status. Dermatophytes establish infection following successful adherence of arthroconidia to the surface of keratinized tissues. The proteolytic enzymes released during adherence and invasion not only ascertain their survival but also allow the persistence of infection in the host. While the cutaneous immune surveillance mechanism, after antigen exposure and presentation, leads to activation of T lymphocytes and subsequent clonal expansion generating effector T cells that differentially polarize to a predominant Th17 response, the response fails to eliminate the pathogen despite the presence of high levels of IFN-γ. In chronic dermatophytosis, antigens are a constant source of stimulus promoting a dysregulated Th17 response causing inflammation. The host-derived iTreg response fails to counterbalance the inflammation and instead polarizes to Th17 lineage, aggravating the chronicity of the infection. Increasing antifungal resistance and recalcitrant dermatophytosis has impeded the overall clinical remission. Human genetic research has the potential to generate knowledge to explore new therapeutic targets. The review focuses on understanding specific virulence factors involved in pathogenesis and defining the role of dysregulated host immune response against chronic dermatophytic infections for future management strategies.

Assessment of the subtilisin gene profile in Trichophyton verrucosum isolated from human and animal dermatophytoses in two-stage multiplex PCR

AIMS

Keratin is a fibrous and recalcitrant structural protein and the third most abundant polymer in nature after cellulose and chitin. Subtilisin-like proteases (SUB) are a group of serine endoproteases, coded by seven genes (SUB1-7), which decompose keratin structures and have been isolated from dermatophytes. Herein, we identified the SUB genes in 30 clinical isolates of Trichophyton verrucosum obtained from human and animal dermatophytosis as well as asymptomatic animal carriers.

METHODS AND RESULTS

We designed and proposed a two-stage multiplex PCR technique to detect all seven genes encoding serine proteases in dermatophytes. The analysis revealed the presence SUB1 and SUB2 amplicons in all strains regardless of the host. In the group of isolates obtained from humans, all seven subtilisin genes were shown in 40% of the strains. In T. verrucosum from asymptomatic animals, none of the isolates showed the presence of all seven subtilisin genes, and only 30% had six genes. In turn, 10% of the isolates from symptomatic animals demonstrated all seven subtilisins amplicons.

CONCLUSIONS

In conclusion, the severity of infection and ability of T. verrucosum to cause dermatophytosis in humans may not be related to specific genes but their accumulation and synergistic effects of their products.

SIGNIFICANCE AND IMPACT OF THE STUDY

Dermatophytes are pathogenic filamentous fungi with capacity to attack keratinized structures such as skin, hair and nails, causing cutaneous superficial infections. Indeed, a biological characteristic of dermatophytes is their ability to invade keratin-rich tissues by producing enzymes. Various degrees of inflammatory responses can be induced exactly by the enzymes. Subtilisin-like proteases are endoproteases, which decompose keratin structures. Our study identifies SUB genes in clinical isolates of T. verrucosum obtained from human and animal dermatophytosis as well as asymptomatic animal carriers.

Skin Immunity to Dermatophytes: From Experimental Infection Models to Human Disease

Dermatophytoses (ringworms) are among the most frequent skin infections and are a highly prevalent cause of human disease worldwide. Despite the incidence of these superficial mycoses in healthy people and the compelling evidence on chronic and deep infections in immunocompromised individuals, the mechanisms controlling dermatophyte invasion in the skin are scarcely known. In the last years, the association between certain primary immunodeficiencies and the susceptibility to severe dermatophytosis as well as the evidence provided by novel experimental models mimicking human disease have significantly contributed to deciphering the basic immunological mechanisms against dermatophytes. In this review, we outline the current knowledge on fungal virulence factors involved in the pathogenesis of dermatophytoses and recent evidence from human infections and experimental models that shed light on the cells and molecules involved in the antifungal cutaneous immune response. The latest highlights emphasize the contribution of C-type lectin receptors signaling and the cellular immune response mediated by IL-17 and IFN-γ in the anti-dermatophytic defense and skin inflammation control.

Genes Encoding Proteolytic Enzymes Fungalysin and Subtilisin in Dermatophytes of Human and Animal Origin: A Comparative Study

Dermatophytes are among the most successful fungal pathogens in humans, but their virulence mechanisms have not yet been fully characterized. Dermatophytic fungi secrete proteases in vivo, which are responsible for fungal colonization and degradation of the keratinized tissue during infection. In the present study, we used PCR to investigate the presence of genes encoding fungalysins (MEP) and subtilisins (SUB) in three dermatophyte species whose incidence is increasing in Europe: the anthropophilic Trichophyton rubrum (n = 58), zoophilic Microsporum canis (n = 33), and Trichophyton benhamiae (n = 6). MEP2 and SUB4 genes were significantly correlated with T. rubrum; MEP3 and SUB1 were mostly frequently harbored by M. canis; and MEP1, 2, and 4 and SUB3-7 were most frequently harbored by T. benhamiae isolates (p < 0.05). Furthermore, MEP1-5 and SUB1-3 genes were significantly more prevalent among human clinical isolates of M. canis (n = 17) than among asymptomatic cat isolates of M. canis (n = 16; p < 0.05). Unidentified MEP and/or SUB genes in some isolates in the current study may suggest that other gene repertoires may be involved in the degradation of keratin. The presented analysis of the incidence of MEP and SUB virulence genes in three dermatophyte species of diverse origins provides an insight into the host-fungus interaction and dermatophyte pathogenesis.