High Intraspecific Genetic Diversity ofNocardia brasiliensis, a Pathogen Responsible for Cutaneous Nocardiosis Found in France: Phylogenetic Relationships by Usingsodandhsp65Genes

Abstract

This study aims at genetic characterization and phylogenetic relationships ofNocardia brasiliensisfocusing by using housekeepingrrs,hsp65,andsodAgenes.N. brasiliensisis the species responsible for 80% of cases of actinomycetoma, one form of cutaneous nocardiosis which occurs mainly in tropical regions reaching immunocompetent patients in which the disease can lead to amputation. We analyze 36 indigenous cases ofN. brasiliensisthat happened in France. Phylogenetic analysis targetingrrsgene showed no robustness at phylogenetic nodes level. However, the use of a concatenation ofhsp65andsodAgenes showed that the tested strains surprisingly ranked in 3 well-defined genotypes. Genotypes 2 and 3 were phylogenetically closer to each other and both diverged from genotype 1 sustained by a high bootstrap of 81%. This last genotype hosts all the cases of pulmonary forms (3), the sole cerebral form, and almost all the cases of immunocompromised patients (3 out of 4). Moreover, excepting one of them, all the strains belonging to this group present a susceptibility to imipenem which is not the case in the other genotypes that rarely count among them strains being susceptible to this drug. The haplotype diversity (Hd) ofhsp65(0.927) andsodA(0.885) genes was higher than that ofrrs(0.824). For this gene, we obtained 16 polymorphic sites whereas, forhsp65andsodAgenes, up to 27 and 29 were identified, respectively. This study reveals that these two genes have an important genetic discriminatory power for the evaluation of the intraspecies genetic variability ofN. brasiliensisand they may be useful for identification purposes at species level. This study also reveals the possible existence of a new species harbored by genotype 1.