Molecular and phenotypic characterization of Phialemonium and Lecythophora isolates from clinical samples

Abstract

Several members of the fungal genera Phialemonium and Lecythophora are occasional agents of severe human and animal infections. These species are difficult to identify, and relatively little is known about their frequency in the clinical setting. The objective of this study was to characterize morphologically and molecularly, on the basis of the analysis of large-subunit ribosomal DNA sequences, a set of 68 clinical isolates presumed to belong to these genera. A total of 59 isolates were determined to be Phialemonium species (n = 32) or a related Cephalotheca species (n = 6) or Lecythophora species (n = 20) or a related Coniochaeta species (n = 1). Nine isolates identified to be Acremonium spp. or Phaeoacremonium spp. were excluded from further study. The most common species were Phialemonium obovatum and Phialemonium curvatum, followed by Lecythophora hoffmannii, Cephalotheca foveolata, and Lecythophora mutabilis.

Fig. 1.

Neighbor-joining tree among D1/D2 domains of the 28S rDNA sequences of the isolates included in Table 1. Branch lengths are proportional to distance. Sequences not generated in this study and obtained from the GenBank database are indicated in parentheses. Type and reference strains are indicated in boldface.

Fig. 2.

(A to E) Phialemonium curvatum (CBS 490.82^T); (A) adelophialides; (B) conidia; (C) adelophialide with inconspicuous collarette; (D) conidia; (E) sporodochial conidioma. (F to H) Lecythophora hoffmannii (CBS 245.38^T); (F) adelophialides with cylindrical collarettes in a hyphal coil; (G) collarette formed directly on the hyphae and conidia; (H) conidia. (I to K) Lecythophora lignicola (CBS 267.33^T); (I) ventricose phialide; (J) adelophialide and discrete phialides; (K) conidia. (L to O) Lecythophora mutabilis (CBS 157.44^T); (L) phialide; (M) adelophialide; (N and O) chlamydospores. (P to R) Cephalotheca foveolata (UTHSC 08-2766); (P) ascoma with ascospores; (Q) adelophialide and conidia; (R) chlamydospore. (S to V) Phialemonium obovatum (CBS 279.76^T); (S) discrete phialides and adelophialides; (T) conidia; (U) chlamydospores; (V) inmature ascomata. Scale bars, A to D, F to O, and Q to U = 5 μm; V = 20 μm; E and P = 100 μm.