Sporothrix spp. Biofilms Impact in the Zoonotic Transmission Route: Feline Claws Associated Biofilms, Itraconazole Tolerance, and Potential Repurposing for Miltefosine

Abstract

Sporotrichosis is the most prevalent subcutaneous mycosis globally, and it is typically caused by direct inoculation of the soil saprophytic fungus Sporothrix spp. into the patients’ skin. However, sporotrichosis has an important zoonotic transmission route between cats and humans in hot-spot endemic areas such as Brazil. Antifungal itraconazole is the first-line treatment; however, it is frequently associated with recurrence after withdrawal, mainly on cats. Biofilms are important resistance structures related to the environmental persistence of most microorganisms. In the present work, we evaluated Sporothrix yeasts’ ability to form biofilms in an ex vivo model of infected claws of cats. Using scanning electron microscopy, we demonstrated the presence of fungal biofilms in the claws of cats diagnosed with sporotrichosis confirmed by isolation of Sporothrix spp. in culture. We present here evidence of antibiofilm activity of miltefosine and suggest its use off-label as an antifungal as a putative alternative to itraconazole against Sporothrix biofilms. Claw contamination could sustain infections through a continuous inoculation cycle between open lesions and cat claws. Our results further support the off-label use of miltefosine as a promising alternative, especially for mycosis refractory to conventional treatment.

Feline sporotrichosis: Characterization of cutaneous and extracutaneous lesions using different diagnostic methods

“…43 Traumatic inoculation can occur through scratching because the retractability of the nails can retain the fungus. 11 Also, inoculation can occur by biting and self-cleaning (licking) because cats can contaminate the oral cavity with the fungus present in the exudate of ulcerative lesions. 4,44 In some cats, it was possible to identify sites with bite wounds, especially on the back and with multiple distributions in the body, including the scrotum, raising the possibility of self-spread, as previously described.…”

Current Progress in Sporothrix brasiliensis Basic Aspects

“…The ability of S. brasiliensis and S. schenckii to form biofilms on pieces of cat's claw has been evaluated. Both species showed different growth kinetics during the biofilm formation, and S. schenckii had higher metabolic activity during the first incubation time [41]. It was observed that S. schenckii and S. brasiliensis have different susceptibility profiles to antifungal drugs, the former being more susceptible in vitro than S. brasiliensis.…”

Milteforan, a promising veterinary commercial product against feline sporotrichosis

“…In addition, it was recently shown that MFS has in vitro fungicidal activity against Sporothrix spp., inhibiting the growth of the mycelial phase of S. brasiliensis , S. schenckii , and Sporothrix globosa (45), and the yeast phase of S. brasiliensis strains resistant to (ITZ) and AMB (46). It was also demonstrated that alone or in combination with potassium iodide, MFS inhibits the biofilm formation of S. brasiliensis , S. schenckii , and S. globosa (47, 48). All of this evidence suggests the potential of MFS for treating sporotrichosis.…”