A comparative study of phenotypic and genotypic characters of environmental and clinical isolates of cryptococcus Spp.

Abstract

With the onset of the HIV epidemic, human infections resulting from environmental exposure to the basidiomycetous yeast Cryptococcus increased significantly. Medical importance of Cryptococcus increased as a consequence of the AIDS epidemic. Cryptococcal infection is believed to be acquired by inhalation of airborne basidiospores from environmental sources which get deposited in the alveoli of host lungs causing infections of pulmonary, visceral or central nervous system. Decaying woods, eucalyptus trees, soil contaminated with bird excreta especially with pigeon droppings provide a favourable environment niche for the growth of Cryptococcus. The present study which involves the isolation and ecology of Cryptococcus has been carried out in Solan, Himachal Pradesh (India) to determine the presence of the yeast in this region from different environmental sources i.e. debris, soil and tree bark as well as pigeon droppings. The selected isolates were preliminary analyzed by using biochemical tests to identify members of Cryptococcus species complex. Then, the identity of the isolates was confirmed using microscopical and further biochemical tests. To know the species level of the isolates, in silico analysis of the large ribosomal subunit (LSU) of 28S rDNA and internal transcribed spacer (ITS) was done. Genetic differences between the isolates were studied by phylogenetic analysis. Phenotypic switching, extracellular enzymes, viz., protease, phospholipase, DNase, hemolysins and a variety of pigments were observed for ATCC, clinical and environmental strains. Ability of Cryptococcus to produce these extracellular enzymes and phenotypic switching may be associated with its virulence. All the strains had shown a variety of color hues. Such a variety of pigmentation exhibited by different species of Cryptococcus may be a possible virulence weapon of the organismand#8223;s pathogenic nature. The detection of resistant strains of C. neoformans, C. albidus, C. terreus, C. laurentii, C. luteolus and C. terrestris to amphotericin B is a sign of emerging resistance among the strains towards the standard antifungal drugs. To the best of our knowledge; the findings present in this research correspond to the first report ever on the isolation of C. flavescens from cactus in Solan. In India, C. albidosimilis and C. terrestris are reported for the first time from this region. Also, this research corresponded to the first epidemiological study of the Cryptococcus species complex in Himachal Pradesh.