Constitutive Melanin in the Cell Wall of the Etiologic Agent of Lobo's Disease

Abstract

Lobo's disease is a chronic granulomatous disease caused by the obligate pathogenic fungus, whose cell walls contain constitutive melanin. In contrast, melanin does not occur in the cell walls of Paracoccidioides brasiliensis when stained by the Fontana-Masson stain.

Phylogenetic Analysis of Lacazia loboi Places This Previously Uncharacterized Pathogen within the Dimorphic Onygenales

“…Those investigators stated that the L. loboi found in dolphins was related to the darkly pigmented (phaeoid, dematiaceous) fungus Cladosporium sphaerospermum. Our phylogenetic analyses, however, placed L. loboi distant from the black fungi, suggesting that, although L. loboi possesses the pigment melanin in its cell walls (28), it is not a phaeoid fungus. This is not unusual, since many fungi, including the human and animal pathogen Cryptococcus neoformans, have melanin in their cell walls and yet are not classified as black fungi (24).…”

Detection of Melanin-Like Pigments in the Dimorphic Fungal PathogenParacoccidioides brasiliensisIn Vitro and during Infection

“…brasiliensis does not stain with the Masson-Fontana stain, an observation which led to the assumption that it does not melanize (38). However, this stain is not very sensitive, and it is not specific for melanin (5), with both nonmelanized and melanized C. neoformans yeasts staining positive (16).…”

Unusual Fungal and Pseudofungal Infections of Humans

“…The epidermis is usually atrophic but may show pseudoepitheliomatous hyperplasia or ulceration. L. loboi is (89,90). H&E stain reveals the thick doubly contoured hyaline cell wall and one or more hematoxylinophilic nuclei (64).…”

“…duboisii (no chains of cells), or Sporothrix schenckeii and H. capsulatum var. capsulatum (both smaller, 2 to 8 m versus 5 to 12 m) (8,64,89,90). These fungi will also grow in culture, whereas L. loboi has never been cultured in vitro (80,89).…”