Research Article: Influence of the cultivation medium and pH on the pigmentation of Trichophyton rubrum

Date Published: September 10, 2019

Publisher: Public Library of Science

Author(s): Oliver Blechert, Hailin Zheng, Xiaohui Zang, Qiong Wang, Weida Liu, Joy Sturtevant.

http://doi.org/10.1371/journal.pone.0222333

Abstract

Trichophyton rubrum is a human pathogenic fungus. As a dermatophyte it causes athlete’s foot, fungal infection of nails, jock itch and ringworm. The pigmentation of T. rubrum is variable and can range from white or yellow to wine-red. We demonstrate that the pigmentation is strongly influenced by pH. Under alkaline conditions, T. rubrum has a red pigmentation, whereas at acid conditions, T. rubrum has a yellow pigmentation. Moreover, the color change immediately from yellow to red by adding NaOH and reverse immediately from red to yellow by adding HCl. We suggest that the chemical compound Xanthomegnin is responsible for red as well for yellow pigmentation in T. rubrum. To figure out, why T. rubrum has red pigmentation on Trichophyton medium, adjust to alkaline, but not on Synthetic-Complete medium, also adjusted to alkaline, we measure the pH of liquid media, adjusted to pH 3.5, 6 and 8, over a period of four weeks. The pH of both cultivation media changes significantly, with a maximum of five pH levels. Whereas the Trichophyton medium, initially adjusted to pH 8, stays alkaline, the pH of the Synthetic-Complete medium drops to acid conditions. The acidification of the SC medium and the alkalization of the Trichophyton medium explains the different pigment color of the T. rubrum colonies.

Partial Text

Trichophyton rubrum (Castellani) Sabouraud 1911 is a human pathogenic fungus. As a dermatophyte it causes athlete’s foot, fungal infection of nails, jock itch and ringworm. To find an appropriate treatment for the disease, an accurate diagnosis is mandatory. Therefore the diagnosis of the fungal infections involves in many cases microscopic examination and fungal cultivation. According to a survey among dermatologists, direct microscopy was the most important diagnostic tools followed by cultivation of the pathogen [1]. Whereas direct microscopy is often sufficient to detect a fungal infection, the identification of the pathogen requires in most cases fungal cultivation. And a correct identification is important, since the treatment approach is dependent on the pathogen [2]. The appearance of T. rubrum is to a certain degree inconsistent and the discrimination from related species is sometimes intricate. Variations in the colony surface, culture pigmentation and conidia production are known [3]. Three factors account principal for variations: the genome, the epigenetics and the environment. Since all of these factors are complex, it is challenging to determine which of the factors are responsible for an observed variation. Moreover, a phenotype can be influenced by all three factors.

The pigmentation of T. rubrum is variable and is influenced by many factors. We demonstrate, that the pigmentation is strongly influenced by the pH. Since the phenotype is quite constant among the fungal strains at constant conditions, but variable among the different conditions, we conclude that the environment is the determining factor in our experiments. At alkaline conditions, T. rubrum has a red pigmentation, whereas at acid condition T. rubrum has a yellow pigmentation.

 

Source:

http://doi.org/10.1371/journal.pone.0222333