SPOROTHRIX SCHENCKII: CHARACTERISTICS, MORPHOLOGY, TREATMENT - BIOLOGY - 2025

Division: Ascomycota

Class: Sordariomycetes

Order: Ophiostomatales

Family: Ophiostomataceae

Genus: Sporothrix

Species: schenckii

Morphology

As it is a dimorphic fungus, it has the ability to appear as mold at room temperature and as yeast at a temperature of 37 ° C.

Colonies of the mold form start as white spots, which then enlarge and become elastic or membranous, grayish-white in color without aerial mycelium.

They later turn dark brown to black as they age because the conidia produce melanin. They finally take on a wet and wrinkled appearance.

Microscopically, the fungus presents a thin, hyaline and septate mycelium, with sessile pyriform microconidia, arranged along the hypha or in the form of a rosette on a short conidiophore, similar to a daisy flower.

Meanwhile, the parasitic or yeast form appears as small budding cells of varying size and with a spindle-shaped appearance.

The cultured form of yeast grows as pink colonies of creamy consistency. This is obtained by sowing the clinical sample directly at 37 ° C on blood agar or by sowing the mycelial phase under these same conditions, demonstrating dimorphism.

On microscopic observation of the yeast-shaped culture, oval, round, or spindle-shaped cells "tobacco shape" are observed as seen in tissue.

Pathogeny

The fungus is acquired by traumatic inoculation through the skin with material contaminated with the fungus. The most frequent event is an injury caused by a puncture with a thorn or a splinter in the hand.

The accident introduces the conidia into the subcutaneous tissue. Conidia bind to the matrix of extracellular proteins such as fibronectin, laminin, and collagen.

There the local multiplication of the fungus occurs and a slow inflammatory process begins. This inflammatory reaction has granulomatous and pyogenic characteristics.

The infection then spreads along the lymphatic vessels from the site of origin, where the inflammatory lesions recur at intervals.

On the other hand, on occasions (1% of cases), dissemination by other routes may occur. The bones, eyes, lungs, and central nervous system can be affected if the fungus reaches these sites.

Rarely does the infection become systemic.

Pathology

Three clinical types are distinguished: cutaneous lymphatic sporotrichosis, localized cutaneous sporotrichosis, and disseminated sporotrichosis.

Cutaneous lymphatic sporotrichosis

It is the most common form of the disease. After trauma there is an incubation period of 3 to 21 days, sometimes months.

The initial lesion is a painless papule that gradually increases in size, until it begins to ulcerate in the center. After a week or more, the lymphatic vessels thicken and pustular or nodular lesions may appear around the site of inoculation or along the lymphatic vessel.

These nodules follow the same process as the initial lesion, ulcerating and taking on the same ulcerative appearance. From here the ulcers become chronic.

Localized cutaneous sporotrichosis

Another way the disease can present is as a limited, solitary nodule that does not involve the lymphatic vessels and does not spread. This lesion indicates some resistance to infection from previous immunity. It is common in endemic areas.

The type of lesion can vary, presenting as infiltrated areas, areas of folliculitis, nodular, papilous or warty crusty lesions. They appear on the face, neck, trunk or arms.

Disseminated sporotrichosis

It is relatively rare, there is hematogenous dissemination, which is why a large number of subcutaneous, hard modules appear, scattered throughout the body.

These lesions increase in size, then soften, and later if they are tripped over and ruptured, they chronically ulcerate with permanent discharge. This infection continues to spread and the patient becomes serious, often causing death, if not treated.

The pulmonary location of sporotrichosis is generally secondary to the skin lesion. However, it is not ruled out that inhalation of conidia may lead to a primary lung disease that later spreads and becomes systemic.

Diagnosis

Sampling

Biopsy of closed nodules or exudates (pus) from open lesions.

Microscopic examination

Samples can be stained with Gomori-Grocott, PAS, hematoxylin-eosin, or Gram, to be able to observe the yeast characteristically in the form of extra tobacco or intracellularly. Which are stained black.

In fact, it is quite difficult to observe the fungus, because the lesions harbor a small amount of the microorganism and the few present can be confused with nuclear fragments of necrotic cells.

However, it can be very helpful in finding asteroid bodies, suggesting the presence of the disease. The asteroid body is formed by Sporothrix schenckii yeasts surrounded by amorphous eosinophilic material in a radial arrangement.

The biopsy also reveals a non-specific or granulomatous inflammatory process with infiltration of lymphocytes, giant cells, fibrosis, etc.

Culture

The growth of Sporothrix schenckii is stimulated by thiamine, pyrimidine, and biotin.

The sample can be seeded on Sabouraud dextrose agar only if the lesion is closed, or containing chloramphenicol or cycloheximide in open lesions at 28 ° C and incubating for 4 to 6 days. After this time mold colonies will develop.

To demonstrate dimorphism, the filamentous form can be seeded on brain heart agar supplemented with blood at 37 ° C, with a wet surface and 5% CO ₂, to obtain the yeast phase. This process may require several rings to be successful.

Molecular Biology Techniques

The polymerase chain reaction (PCR) technique can be used to diagnose the disease.

Treatment

The disease was treated for a long time with potassium iodide solution. Today itraconazole is treated for all forms of the disease.

However, pulmonary or systemic infection additionally requires amphotericin B initially and is followed by itraconazole.

Pregnant women are treated with amphotericin B.

Treatment should be completed between 3 to 6 months.

References

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7. Wikipedia contributors. Sporothrix schenckii. Wikipedia, The Free Encyclopedia. April 16, 2018, 10:19 UTC. Available at: en.wikipedia.org
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