PubMed Health⌕ Search

Biomedical subjects

K R Joshi

Publications and source records attributed to K R Joshi.

At least 55 records · Page 3Linked to original sources
PubMed1975

The ultrastructure of Candida krusei.

Various methods of chemical fixation and freeze-drying of Candida krusei were compared to determine the most appropriate method for the ultrastructural investigation of the thick walled organisms of this genus. Freeze-drying without chemical fixation was of little value because of insufficient variation in electron density. Potassium permanganate was able to penetrate the intact cell but failed to show cytoplasmic glycogen and lipid and some details of the cell wall. While normal glutaraldehyde, formaldehyde and osmium tetroxide treatment failed to permeate and preserve intracellular structures, several cycles of rapid freezing (- 155 degrees C) and thawing followed by glutaraldehyde fixation and osmium tetroxide post-fixation demonstrated the intracellular details of the majority of cells so treated.

Candida↗
PubMed1975

The ultrastructure of Prototheca wickerhamii.

Two clinical isolates from Prototheca wickerhamii were freeze-dried, fixed and studied by electron microscopy and were also examined growing in culture medium by phase contrast light microscopy. Resting spores placed on fresh medium developed cytoplasmic extensions which sequestrated before proliferation occurred. In the presence of adequate nutrients vegetative spores grew and subdivided to form up to 12 endospores within large sporangia which ruptured to release free spores every 5--6 hours. These proliferating or vegetative spores contained much more endoplasmic reticulum and mitochondria than the resting spores which contained more lipid, and often starch granules as well, but relatively few membranous organelles.

Cell Membrane↗
PubMed1975

The morphology of colony variants of three species of Candida.

The colonies of 12 isolates of 3 Candida spp. with variant colony forms were studied by scanning and transmission electron microscopy. Small colonies were formed by 4 isolates each of C. albicans and C. parapsilosis and by 1 of C. tropicalis. These had an abnormally high proportion of degenerate yeast cells with an associated increase in granular cytoplasmic material intercellularly. The increased matrix in these small colonies formed a thick superficial coat over the organisms. Rough colonies were formed by 1 isolate each of C. albicans, C. tropicalis and C. parapsilosis. The convoluted regions of these colonies contained many pseudohyphal cells but few degenerate cells and little granular or fibrillar material in their intercellular matrices. The shape of colonies of Candida spp. may be altered by variations in the viability or the morphology of the organisms.

Candida↗
PubMed1975

Intercellular matrix in colonies of Candida.

The histochemistry and fine structure of typical colonies of six species of Candida were studied, using a total of 31 clinical isolates. The colonies consisted of viable and degenerate cells which lay in an intercellular matrix. This matrix was made up of amorphous, granular, and fibrillar components, the relative proportions and total amount of which varied from species to species. The cells of all species were surrounded by a zone of homogeneous amorphus material, which may be a highly cross-linked carbohydrate. This separated intact cells from irregularly distributed granular debris derived from the cytoplasm of degenerate cells. Focal cellular degeneration and associated granular debris were present within the colonies of all species and were most common in the surface layers of cells of colonies of C. albicans and C. tropicalis. The large amounts of intercellular matrix in this region formed a surface coat on colonies of these two species. Intercellular strands of cell wall material, and to a lesser extent other membranous elements from degenerate cells, formed a prominent fibrillar meshwork in the colonies of C. albicans and C. tropicalis, but were less common in those of C. pseudotropicalis and C. guilliermondii and seldom seen in those of C. parapsilosis and C. krusei.

Candida↗
PubMed1975

The morphological identification of pathogenic yeasts using carbohydrate media.

Eight isolates of C. albicans were used to determine the frequency with which germ tube formation occurred: on rice extract -Tween 80 agar, on its components, and on 1% bactopeptone agar after three hr at 37 degrees C; in 0.5% aqueous solution of various carbohydrates; in various concentrations of glucose; on 0.5 and 0.1% glucose agar and on various types of agar alone. Subsequently 250 isolates of yeast of the genera Candida, Torulopsis, Trichosporon, Cryptococcus, and Saccharomyces, which were obtained from a clinical laboratory, were spread on rice extract -Tween 80 agar and on 0.1% glucose agar and covered with coverslips. Direct microscopic examination after incubation for three hours at 37 degrees C demonstrated germ tube formation by all 140 isolates of C. albicans, but by none of the other yeasts. The characteristic features of the pseudomycelia of isolates of Candida and Trichosporon were evident on reexamination after a further 45 to 69 hours at room temperature (22 degrees C). These morphological observations suggested the identity of the isolates of Torulopsis, Cryptococcus, and Saccharomyces but identified virtually all (98.2%) of those of the genera which formed pseudomycelia. Of the latter group only four isolates required fermentation and assimilation tests to determine whether they were C. parapsilosis (1) or C. guilliermondii (3).

Agar↗
PubMed1973

Scanning electron microscopy of colonies of six species of Candida.

Thirty strains of six species of Candida isolated from patients were cultured for 60 h on Sabouraud agar, freeze-dried, and examined with a scanning electron microscope. The colonies were circular (Candida albicans, C. guilliermondii) or oval (C. tropicalis, C. pseudotropicalis, C. krusei, C. parakrusei) in outline, and those of C. pseudotropicalis and C. krusei had an irregular outline due to a peripheral pseudomycelium. The morphology of individual microorganisms was examined at the margins and apex of those species which lacked a surface coat (C. pseudotropicalis, C. krusei, C. parakrusei, C. guilliermondii), and through cracks in the surface coating of those which showed a surface coat (C. albicans, C. tropicalis). All species showed buds, bud scars, and interconnecting intercellular processes, but were generally spherical (C. albicans, C. tropicalis) or ovoid (C. pseudotropicalis, C. krusei, C. parakrusei, C. guilliermondii) in fixed preparations. In unfixed material, individual organisms were almost invariably indented. Fixation with 3% glutaraldehyde and washing before freeze-drying caused partial removal of the surface coating of colonies of C. albicans and C. tropicalis, which persisted only as irregular sheets or as a filamentous meshwork. This filamentous meshwork was also present among the organisms of colonies of C. albicans, C. tropicalis, and C. pseudotropicalis. It is concluded that these filaments represent the precipitation or unmasking of some component of the intercellular matrix of these organisms.

Candida↗