Stability of Tandemly Repetitive Subelement PCR Patterns in Trichophyton rubrum over Serial Passaging and with Respect to Drug Pressure

Abstract

Trichophyton rubrum is the most significant agent of dermatomycoses worldwide, primarily causing tinea pedis and tinea unguium. PCR analysis of tandemly repetitive subelements (TRS) within the rDNA nontranscribed spacer region is a major tool for molecular typing of T. rubrum. The aim of this study was to investigate the stability of TRS PCR patterns by analyzing isogenic strains of T. rubrum. Twenty-seven groups of isogenic T. rubrum strains were examined, each composed of an original clinical isolate and its 3 subcultures, maintained on a drug-free medium, a medium containing fluconazole and itraconazole. TRS typing was performed for the original strains and their subcultures grown after 12 passages, at 4-week intervals, on respective media. To add more objectivity to the results, TRS typing for each of the isogenic strain was performed three times, using DNA isolated from three different colonies. Among 27 groups of isogenic strains, all but one were exclusively composed of strains with identical TRS-1 and TRS-2 PCR patterns. In one group, 3 isolates from the last, twelfth passage had identical TRS-1 PCR profiles (type 1), yet different TRS-2 PCR profiles, as compared with the original strain (type I vs. type II). The mechanism underlying the genotype switch was a deletion of a single repeat unit in the TRS-2 locus, as evidenced by sequence analysis. In the interpretation of TRS typing results, microevolutionary events need to be taken into account, urging drawing epidemiological conclusions with caution and in conjunction with other genotyping data and traditional contact tracing information.

Trichophyton rubrumDNA strain switching increases in patients with onychomycosis failing antifungal treatments

“…Although culture has traditionally supported T. rubrum genotype stability (i.e. lack of microevolution), and the DNA strain types in this study remained genetically stable over 18 months in culture, a recent report has detected a deletion of an rDNA tandemly repetitive subelement (TRS) upon repeated in vitro exposure to terbinafine. However, it is more likely that coinfecting T. rubrum DNA strains may be present in onychomycosis, undetected in culture and subsequently isolated in a serial culture .…”

“…1 Genetic strain typing methods have revolutionized epidemiological studies of dermatophyte infections as they are sensitive enough to distinguish a high number of DNA strain types left uncharacterized by morphological identification, which is limited by the cultural stability and differentiation of strains. 2 T. rubrum DNA strain types have been characterized using a number of methods, [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] but no correlation between DNA strain type and culture morphology has been detected, 10,14,19 even after multiple passages over the course of a year. 20 Geographical trends have been found where isolates from Europe have been distinguished from Japanese isolates, 16 African isolates distinguished from non-African isolates, 10,12 and Japanese isolates distinguished from Chinese isolates.…”

High Genetic Diversity among Stenotrophomonas maltophilia Isolates from Single Hospital: Nosocomial Outbreaks or Genotypic Profile Changes during Subcultures

“…For this reason, the genomic properties of the bacteria to be analysed by molecular epidemiological methods must be thoroughly known. Genotypic changes related to mutations, some of which were evidenced by sequence analysis, were demonstrated for several microorganisms with serial passages including S. aureus , Trichophyton rubrum , satellite tobacco mosaic virus ( 20 – 21 ).…”

Highly Discriminatory Variable-Number Tandem-Repeat Markers for Genotyping of Trichophyton interdigitale Strains

“…Recently, microsatellite markers have proven their utility for the detection of variability among dermatophytes (13). In other human-pathogenic dermatophytes, multilocus microsatellite typing has proved to be a promising tool for uncovering intraspecific diversity due to the high mutation rate of those markers (14).…”