Genetic Characterization of Microsporum canis Clinical Isolates in the United States

Abstract

Microsporum canis is the primary agent causing dermatophytosis in cats, and also infects humans, dogs, and other species. Assessment of genetic variation among M. canis isolates in the United States has not been conducted. Further, M. canis mating type and assessment of disease severity associated with genotypic characteristics have not been rigorously evaluated. We therefore isolated M. canis from 191 domestic cats across the US and characterized genotypes by evaluation of ITS sequence, MAT locus, and microsatellite loci analysis. The genes SSU1 and SUB3, which are associated with keratin adhesion and digestion, were sequenced from a subset of isolates to evaluate potential genetic associations with virulence. Analysis of microsatellite makers revealed three M. canis genetic clusters. Both clinic location and disease severity were significant predictors of microsatellite variants. 100% of the M. canis isolates were MAT1-1 mating gene type, indicating that MAT1-2 is very rare or extinct in the US and that asexual reproduction is the dominant form of replication. No genetic variation at SSU1 and SUB3 was observed. These findings pave the way for novel testing modalities for M. canis and provide insights about transmission and ecology of this ubiquitous and relatively uncharacterized agent.

Keywords: Microsporum canis; cats; dermatophytosis; mating-type; multilocus microsatellite typing.

Figure 1

Representative images of microsatellite genotypes. MS4 peaks of unrelated isolates (CBS 113480, BC3, CA107, MA3) showing varying allele sizes at 107 bp, 159 bp, 127 bp, and 121 bp, respectively. CBS = Westerdijk Fungal Biodiversity Centre; BC = Boulder County, CO; CA = California; MA = Massachusetts.

Figure 2

Microsatellite locus allelic diversity varies among Microsporum canis isolates. Allele sizes for microsatellite loci (MS) 1–8 for each sample are plotted with Boulder County, CO (n = 6); California (n = 122); Larimer County, CO (n = 4); Massachusetts (n = 5); New Jersey (n = 1); New Mexico (n = 36); Weld County, CO (n = 9). The microsatellite loci had the following ranges: 105–117 bp (MS1), 95–101 bp (MS2), 110–116 bp (MS3), 103–161 bp (MS4), 96–106 bp (MS5), 105–115 bp (MS6), 121–127 bp (MS7), and 112–118 bp (MS8).

Figure 3

Disease severity and location associated with microsatellite genotype. Distance-based redundancy analysis showed significant association between disease severity and microsatellite variation. (A)—samples colored based on clinic location. (B)—samples colored by disease severity. Locations included in study are California (CA); New Mexico (NM); Boulder County, CO (BC); Larimer County, CO (LC); and Massachusetts (MA). Position on the plot for each sample depicts genetic differentiation. Arrow = disease severity increases direction of arrow.

Figure 4

Evidence of separation based on clinic location for Boulder, Massachusetts, and part of California. Principal component analysis (PCA) plot for microsatellite regions, with samples colored according to clinic. One sample from Massachusetts was an outlier. The portion of California samples that appear distinct were collected in the same month. Locations included in study are California; New Mexico; Boulder County, CO; Larimer County, CO; Weld County, CO; New Jersey; and Massachusetts.

Figure 5

Samples from Boulder County, CO and a portion of California clustered apart from other sampled locations. Structure plots with K values 3–5. The amount of vertical color for each sample corresponds with the percentage of belonging to that color cluster. Admixture increased for plots using K = 4 and K = 5. Locations included in study were Boulder County, CO (1); California (2); Larimer County, CO (3); Massachusetts (4); New Jersey (5); New Mexico (6); and Weld County, CO (7).