Ultrastructural changes in Paracoccidioides brasiliensis yeast cells attenuated by gamma irradiation

Abstract

Paracoccidioides brasiliensis is a thermally dimorphic fungus agent of paracoccidioidomycosis, a deep-seated systemic infection of humans with high prevalence in Latin America. Until now no vaccine has been reported. Ionizing radiation can be used to attenuate pathogens for vaccine development and we have successfully attenuated yeast cells of P. brasiliensis by gamma irradiation. The aim of the present study was to examine at ultrastructural level the effects of gamma irradiation attenuation on the morphology of P. brasiliensis yeast cells. Paracoccidioides brasiliensis (strain Pb-18) cultures were irradiated with a dose of 6.5 kGy. The irradiated cells were examined by scanning and also transmission electron microscopy. When examined 2 h after the irradiation by scanning electron microscopy, the 6.5 kGy irradiated cells presented deep folds or were collapsed. These lesions were reversible since when examined 48 h after irradiation the yeast had recovered the usual morphology. The transmission electron microscopy showed that the irradiated cells plasma membrane and cell wall were intact and preserved. Remarkable changes were found in the nucleus that was frequently in a very electrondense form. An extensive DNA fragmentation was produced by the gamma irradiation treatment.

Immunogenicity of an Electron Beam Inactivated Rhodococcus equi Vaccine in Neonatal Foals

“…Although variation in severity of changes involving the ultrastructural components of the cell wall was found between the irradiated and heat-inactivated groups, morphologic changes in internal structures only were detected in the heat-inactivated bacteria. Preservation of the cell wall integrity after eBeam irradiation has also been shown for Paracoccidioides brasiliensis [47], and membrane damage of Bacillus spp. spores was observed only at high doses of eBeam irradiation [45].…”

New advances in the development of a vaccine against paracoccidioidomycosis

“…When examined 2 h after irradiation the cells showed deep folds or collapsed. The plasma membrane and cell wall were intact, but an extensive DNA fragmentation was found (Demicheli et al, 2007). The use of attenuated yeast cells by gamma-irradiation induced a long lasting protection in BALB/c mice (Demicheli et al, 2006; do Nascimento Martins et al, 2007).…”

Changes in Ralstonia solanacearum Cells and its Pathogenicity Due to Exposure to Extremely Low Frequency Electromagnetic Field

“…The morphological changes of control group and group exposed to 1 Hz QAMW for 1 h Hz QAMW have been determined using TEM. In order to prepare the bacterial sample to be examined by TEM, the sample should undergo some processing (Demicheli et al, 2007). The processing of bacterial cells (control and exposed) began after 1h of exposure, where the bacterial cells were collected and washed three times in PBS.…”