Molecular and morphological identification of Colletotrichum species of clinical interest

Abstract

Colletotrichum species have caused human infections in recent years. Because of the difficulties in recognizing them in vitro, we have designed a quick and unambiguous molecular test, based on the amplification of a specific fragment of the internal transcribed spacer 1 region, to distinguish any Colletotrichum isolate from other fungi, including the common pathogenic species. Analysis of the sequences of the ribosomal DNA (rDNA) fragment showed sufficient variability to clearly separate the five species of Colletotrichum that are of clinical interest, i.e., Colletotrichum coccodes, C. crassipes, C. dematium, C. gloeosporioides, and C. graminicola. Sequencing of the D1-D2 region of the large-subunit rDNA gene also supported these results. Additionally, we reviewed the most suitable morphological characteristics for the in vitro identification of these increasingly important opportunistic fungi.

FIG. 1.

Conidia and appressoria of Colletotrichum species of clinical interest. (A) C. coccodes; (B) C. crassipes; (C) C. dematium; (D) C. gloeosporioides; (E) C. graminicola.

FIG. 2.

Unrooted neighbor-joining tree of 15 sequences of Col products of rDNA from Colletotrichum species. The branch lengths are proportional to genetic distance, which is indicated by the bar. Bootstrap values (percentages of 1,000 replications) are indicated at the internodes.

FIG. 3.

Unrooted neighbor-joining tree of 10 sequences of D1-D2 regions of LSU rDNAs from Colletotrichum species. The branch lengths are proportional to genetic distance, which is indicated by the bar. Bootstrap values (percentages of 1,000 replications) are indicated at the internodes.