Question

Patient A

A 44 yr old woman presents to the office for evaluation of skin growths on her right arm. She reports that a few weeks ago she developed some small, red bumbs on her right palm. This then ulcerated, but it never was painful. She has been putting topical antibiotics on the area with little effect. Recently she noticed new growths extending up her forearm that appear similar to the original lesion. She is employed as a florist and has been for the last few years.

1. What fungal pathogen might you suspect the patient is suffering from?

2. A microscopic examination of the biopsy from the lesion would most likely reveal what characteristic forms

3. If a culture was performed, how might the characteristic forms detected be different?

4. How do you differentiate this group of fungi from other fungi? (Hint: Temperature, growth rate, color, hyphae, others)

Answer 1

The fungal pathogen that is suspected is Sporothrix which causes sporotrichosis.

Sporotrichosis (also known as “rose gardener’s disease”) is an infection caused by a fungus called Sporothrix. This fungus lives throughout the world in soil and on plant matter such as sphagnum moss, rose bushes, and hay.

Types of sporotrichosis

• Cutaneous (skin) sporotrichosis is the most common form of the infection. It usually occurs on a person’s hand or the arm after touching contaminated plant matter.
• Pulmonary (lung) sporotrichosis is rare but can happen after someone breathes in fungal spores from the environment.
• Disseminated sporotrichosis occurs when the infection spreads to another part of the body, such as bones, joints, or central nervous system. This form of sporotrichosis usually affects people with health problems or who take medicines that lower the body’s ability to fight germs and sickness, such as people living with HIV

Sporotrichosis usually affects the skin or tissues underneath the skin. The first symptom of cutaneous (skin) sporotrichosis is usually a small, painless bump that can develop any time from 1 to 12 weeks after exposure to the fungus. The bump can be red, pink, or purple, and usually appears on the finger, hand, or arm where the fungus has entered through a break in the skin. The bump will eventually grow larger and may look like an open sore or ulcer that is very slow to heal. Additional bumps or sores may appear later near the original one.

Direct smear examination of pus or biopsy specimen for causative fungus is not diagnostic because of paucity of fungal cells. Fine needle aspiration cytology from a lesion, particularly in extracutaneous or disseminated forms, may occasionally show epithelioid cell granuloma, asteroid bodies, and/or yeast cells and cigar shaped bodies when stained with periodic acid-Schiff (PAS) or Gomori-methenamine silver (GMS) stains.

The various Sporothrix species appear similar in morphology, but only S. schenckii is pathogenic to humans. S. schenckii can be grown from skin biopsy or other clinical samples (sputum, pus, synovial fluid/biopsy, bone drainage/biopsy, and cerebrospinal fluid) on Sabouraud's glucose agar (SDA), brain heart infusion agar, or Mycosel at 25°C and the growth is visible in 3–5 days to 2 weeks . Incubation of cultures at 37°C in blood glucose-cysteine agar or brain-heart infusion broth will produce its yeast form. The initial cream-colored colonies grown on SDA at 25°C are smooth and moist but turn brown/black after a few weeks due to melanin production that protects it from phagocytosis and killing by human monocytes and macrophages and extracellular proteinases.

Microscopically, in lactophenol cotton blue mounts, S. schenckii appears as delicate branching septate hyphae with slender, short, conidiophores with tapering tips and surrounding pyriform conidia in a flower-like arrangement or as individual thick-walled, dark brown conidia attached directly to the hypha often in dense sleeve-like pattern. In practice, S. schenckii is usually identified by its characteristic colony morphology, microscopic appearance and temperature dimorphism that is, its ability to exist as a mold at 25°C (room temperature) and as yeast at 37°C (in host tissues)