Coccidioides posadasii de origem clínica e ambiental : um estudo da diversidade genética

Abstract

Coccidiodomycosis is a systemic infection, predominantly pulmonary, caused by the geophilic and dimorphic fungi, Coccidioides immitis and Coccidioides posadasii. In Brazil, coccidioidomycosis is associated with semi-arid areas in the Northeastern region of this country, which is considered one of the endemic areas of this disease in South America. These pathogens are morphologically indistinguishable species, but they exhibit molecular differences. Different molecular techniques have been described for the characterization of these species. The nuclear ribosomal DNA (rDNA) from Coccidioides spp. has been described as an important molecular marker for the identification, taxonomy and phylogeny. Currently, there are still shortages of maps for epidemiological approaches in order to direct the correlation between populations of Coccidioides spp. and the outbreaks of coccidiomycosis. Given the above, this study aimed at performing the molecular identification of 18 clinical and environmental isolates of C. posadasii, from Northeastern Brazil, maintained in the fungal collection of the Specialized Medical Mycology Center (CEMM), through PCR, as well as, to analyze the genetic diversity of these isolates by sequencing of 18S-28S regions of nuclear rDNA. The identification of the isolates was performed through PCR, using specific primers Coi9-1F and Coi9-R. The sequencing of the 18S-28S rDNA regions was performed through the method of chain termination by dideoxynucleotides, using the kit DYEnamicTM ET terminators cycle sequencing (GE Healthcare). The results confirmed the identification of all strains included in this study as belonging to the species C. posadasii. The phylogenetic tree based on 18S-28S rDNA region of C. posadasii from CEMM and Coccidioides spp. from Genbank. reveals the formation of a unique cluster encompassing the following strains CEMM 05-2-063, CEMM 05-2-064, CEMM 05-2-066 and CEMM 05-2-065, in a properly sustained branch, which apparently seems to group these isolates according to their geographical origin. The strains of C. posadasii showed lower genetic divergence in the ITS1 and ITS2 regions, when compared to strains of C. immitis. Analyses did not detect differences between strains of clinical origin and those of environmental origin. Further studies involving the analysis of fast evolving markers, such as microsatellites, can provide evidences to determine whether the groups found in this study are derived from a lineage of clonal reproduction.