Conidiobolus coronatus

Entomophthora coronata.

The species of the genus Conidiobolus produce characteristic multinucleate primary and secondary (replicative) conidia on top of unbranched conidiophores.

Each subspherical conidium is discharged as a result of the pressure developed within the conidium, and each bears a more or less prominent papilla after discharge (King 1983).

The genus contains 27 species, however only Conidiobolus coronatus, C. incongruus and C. lamprauges have been reported as causative agents of human and animal infection. A morphological identification key for clinical isolates was given by Vilela et al. (2010), and an overview of the taxonomy of the genus by Nie et al. (2020).

Conidiobolus coronatus is commonly present in soil and decaying leaves. It has a worldwide distribution especially tropical rain forests of Africa. Human infections are usually restricted to the rhinofacial area. However, there are reports of disseminated infection in immunocompromised patients. All human infections have been confined to the tropics (Shaikh et al., 2016).

RG-2 organism.

Conidiobolus culture

Culture of Conidiobolus coronatus showing satellite colonies from forcibly discharged conidia.

Morphological description:
Colonies of C. coronatus grow rapidly and are flat, cream-coloured, glabrous becoming radially folded and covered by a fine, powdery, white surface mycelium and conidiophores. The lid of the petri dish soon becomes covered with conidia, which are forcibly discharged by the conidiophores. The colour of the colony may become tan to brown with age. Conidiophores are simple forming solitary, terminal conidia which are spherical, 10 to 25 µm in diameter, single-celled and have a prominent papilla. Conidia may also produce hair-like appendages, called villae. Conidia germinate to produce either: (1) single or multiple hyphal tubes that may also become conidiophores which bear secondary conidia; or (2) replicate by producing multiple short conidiophores, each bearing a small secondary conidium.

Conidiobolus microscopy

Spherical conidia with hair-like appendages (villae) and prominent papillae characteristic of Conidiobolus coronatus.

Molecular identification:
ITS sequencing is useful for identification of most clinical isolates.

Emmons and Bridges (1961), King (1983), McGinnis (1980), Rippon (1988), Kwon-Chung and Bennett (1992), de Hoog et al. (2000, 2015), Ellis (2005a), Vilela and Mendoza (2018).