A previously healthy 52-year-old woman comes to the physician because of a 1-week history of productive cough, fevers, and malaise. She has smoked one pack of cigarettes daily for 35 years. Her temperature is 39°C (102.2°F). Diffuse inspiratory crackles are heard bilaterally. Her leukocyte count is 14,300/mm3. Sputum analysis shows numerous polymorphonuclear leukocytes and a few squamous epithelial cells. An x-ray of the chest shows bilateral patchy consolidations. Which of the following findings on sputum culture is most consistent with this patient's respiratory symptoms?

Encapsulated, pleomorphic, gram-negative coccobacilli

Anaerobic gram-positive, branching, filamentous bacilli

Gram-positive, alpha-hemolytic, optochin-resistant cocci in chains

Pseudohyphae with budding yeasts at 20°C

Gram-positive, catalase-positive, coagulase-negative cocci in clusters

A 34-year-old woman presents with multiple round, scaly patches on her chest and back. The lesions are hypopigmented and slightly pruritic. KOH preparation of skin scrapings shows short, angular hyphae. Which of the following best describes the causative organism's morphology in culture?

Branching, septate hyphae with characteristic 'spaghetti and meatballs' appearance

Non-septate hyphae with sporangiospores

Branching, septate hyphae with tear-drop microconidia

Pseudohyphae with blastoconidia

A previously healthy 5-year-old boy is brought to the physician because of a 2-day history of itchy rash and swelling on his left lower leg. His mother says the boy complained of an insect bite while playing outdoors 3 days before the onset of the lesion. His immunizations are up-to-date. He is at the 50th percentile for height and the 85th percentile for weight. He has no known allergies. His temperature is 38.5°C (101.3°F), pulse is 120/min, and blood pressure is 95/60 mm Hg. The lower left leg is swollen and tender with erythema that has sharply defined borders. There is also a narrow red line with a raised border that extends from the lower leg to the groin. The remainder of the examination shows no abnormalities. Which of the following is the most likely cause of these findings?

Streptococcus pyogenes infection

Staphylococcus aureus infection

A 31-year-old female undergoing treatment for leukemia is found to have a frontal lobe abscess accompanied by paranasal swelling. She additionally complains of headache, facial pain, and nasal discharge. Biopsy of the infected tissue would most likely reveal which of the following?

Spherules containing endospores

Budding yeast with a narrow base

A previously healthy 24-year-old woman comes to the physician because of a 1-day history of nausea and weakness. She is sexually active with 2 male partners and uses an oral contraceptive; she uses condoms inconsistently. Her last menstrual period was 4 days ago. Her temperature is 38.4°C (101°F). Physical examination shows right costovertebral angle tenderness. Pelvic examination is normal. Which of the following is the most likely cause of this patient's condition?

Ascending bacteria from the bladder

Noninfectious inflammation of the bladder

Ascending bacteria from the endocervix

Decreased renal calcium reabsorption

Sporothrix schenckii complex for USMLE Step 3: High-Yield Microbiology Lessons

Microbiology - The Thorny Impostor

A thermally dimorphic fungus, existing in two forms based on temperature.

Mold in the Cold (25°C): Found on vegetation (rose thorns, sphagnum moss). Appears as branching, septate hyphae with rosette-like conidia.
Yeast in the Heat (37°C): In vivo form seen in human tissue. Microscopically appears as pleomorphic, cigar-shaped budding yeasts.

Sporothrix schenckii cigar-shaped yeast cells

⭐ Remember "rose gardener's disease": A primary nodule appears after a thorn prick, followed by a chain of subcutaneous nodules ascending along the lymphatic drainage.

Pathogenesis & Transmission - A Prickly Situation

Transmission: Acquired via traumatic inoculation with contaminated plant matter (thorns, splinters) or soil. The classic association is "rose gardener's disease."
Initial Lesion: Begins as a small, painless papule or nodule at the site of entry. This primary lesion may later ulcerate.
Lymphocutaneous Spread: The infection characteristically ascends along lymphatic channels, forming a linear chain of secondary nodules.

⭐ In tissue, S. schenckii can be seen as cigar-shaped yeasts. Occasionally, these are surrounded by eosinophilic material, forming "asteroid bodies" (Splendore-Hoeppli phenomenon).

Clinical Presentation - The Gardener's Curse

Lymphocutaneous Sporotrichosis (75% of cases):
- Initial lesion: A small, painless papule or nodule appears at the trauma site.
- This primary lesion may ulcerate.
- Secondary lesions: A chain of subcutaneous nodules develops along the path of lymphatic drainage, a classic sign known as ascending lymphangitis.

Lymphocutaneous sporotrichosis lesions on arm

Other Forms:
- Fixed Cutaneous: A single, localized plaque that doesn't spread along lymphatics.
- Disseminated: Rare, affecting immunocompromised patients. Can involve joints, lungs, and the CNS.

⭐ On histopathology, look for asteroid bodies (Splendore-Hoeppli phenomenon) and pleomorphic yeasts, including the classic "cigar-shaped" forms, especially at 37°C.

Diagnosis - Spotting the Spores

Culture: Gold standard for diagnosis. Samples of pus, tissue, or exudate are cultured at two temperatures to demonstrate thermal dimorphism (mold at 25°C, yeast at 37°C).
Biopsy & Histopathology:
- Reveals mixed suppurative and granulomatous inflammation.
- Key finding: Pleomorphic yeasts, including the classic cigar-shaped yeast.
- May show asteroid bodies: yeast cells surrounded by eosinophilic material (Splendore-Hoeppli phenomenon).

Sporothrix schenckii: Yeast, asteroid body, cigar-shaped

⭐ Asteroid bodies are highly suggestive but not pathognomonic for sporotrichosis; they represent an antigen-antibody reaction also seen in other infections.

Treatment - Kicking the Itch

💡 Classic alternative for cutaneous disease: Saturated Solution of Potassium Iodide (SSKI).

⭐ Treat with Itraconazole for 3-6 months; therapy must continue for 2-4 weeks after all lesions have resolved to prevent relapse.

High‑Yield Points - ⚡ Biggest Takeaways

Dimorphic fungus; branching hyphae at 25°C, cigar-shaped budding yeast at 37°C.

Causes sporotrichosis, the "rose gardener's disease," from traumatic inoculation.

Spreads via lymphatics, causing a chain of subcutaneous nodules (lymphocutaneous sporotrichosis).

Biopsy may show asteroid bodies-yeast cells surrounded by eosinophilic material.

Culture on Sabouraud agar is the diagnostic standard.

Itraconazole is the treatment of choice for cutaneous and lymphocutaneous forms.

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