Microbiology & infectious diseases

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Contributed by Amaro Nunes Duarte-Neto, M.D., Ph.D.

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A premature newborn (33 weeks of pregnancy) was hospitalized in the intensive care unit after birth with a low Apgar score and respiratory insufficiency. He was maintained on mechanical ventilation; central venous lines were set and he was fed with a nasogastric tube. On the eighth day, he developed abdominal distension, had bloody stool and was diagnosed with necrotizing colitis, which required large spectrum antibiotics and surgical treatment. He was then started on total parenteral nutrition. After a week, the newborn developed a new sepsis with alveolar - perivascular infiltrates on the lungs. A bronchoalveolar lavage showed mixed inflammatory infiltrate surrounding structures, which are shown in the image above. What is the most likely etiological agent of this sepsis?

1. Aspergillus spp.
2. Candida spp.
3. Gram positive cocci
4. Histoplasma capsulatum

B. Candida spp. There are spores, pseudohyphae and hyphae in the figure. Candida spp. are the most common nosocomial fungal infections and their main characteristic is forming spore, pseudohyphae and hyphae in tissues. Answer D is incorrect because H. capsulatum is a yeast in tissue and rarely produces pseudohyphae, even in cases with high fungal burden; moreover, it is not a common fungal nosocomial infection. Answer C is incorrect because gram positive cocci do not have a yeast-like aspect in tissues, as they are much smaller, without budding. Gram positive cocci form colonies in tissues. Answer A is incorrect because Aspergillus spp. are hyaline hyphae fungal agents, with acute dichotomous branching and multiple regular septa. Candida spp. can form hyphae but they are associated with spores and pseudohyphae. The Candida spp. hyphae are amphiphilic, randomly branching and without septa.

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Reference: Candida auris

A man with idiopathic pulmonary fibrosis requiring high dose corticosteroids was hospitalized with fever and sepsis. The blood culture identified Candida spp. and in a few days, the strain was identified as C. auris by sequencing the D1 / D2 region of the 28s ribosomal DNA. In parallel, the patient developed bilateral pulmonary infiltrates with respiratory insufficiency and was put under mechanical ventilation. A bronchoalveolar lavage and biopsy were performed, showing round to oval yeasts, with thick walls and narrow based single budding, associated with mononuclear inflammatory reaction. Rare forms showed germinative tubes. Which stain should be requested to confirm the etiology of this fungal infection?

1. Gram stain
2. Mucicarmine stain
3. Von Kossa stain
4. Ziehl-Neelsen stain

B. Mucicarmine stain. Cryptococcus spp. has mucicarmine positive capsule. It causes opportunistic infections in patients who receive high doses of corticoids, mainly pneumonia and meningitis. Cryptococcosis can occur with other opportunistic infections in the same patient. When there is high C. neoformans tissue burden, some yeasts can form germ tubes, which mimic Candida spp. pseudohyphae. Answer A is incorrect because Gram stain can label all fungal species (as they are all gram positive) and does not give a specific diagnosis. Answers C and D are incorrect because these stains (von Kossa and Ziehl-Neelsen) do not stain fungal forms.

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Reference: Candida auris