摘要:

AbstractOral candidosis has become an increasingly important problem in HIV-infected individuals. At present, the small body of published literature on the characterization of theCandidastrains and species found in HIV+patients is full of confusion and contradictions. Some of these difficulties are the result of the methodological shortcomings of a number of the techniques that have been used. Examples of the problems that may be encountered on primary isolation and subculture are described and the drawbacks associated with the systems used to date for phenotypingCandidaare quoted. While molecular characterization techniques would appear to offer a reliable and objective alternative, they too have their strengths and weaknesses. An attempt is made to summarize the progress that has been made recently in the detection and identification ofCandida albicansand also thenon-albicansspecies from HIV-infected individuals. What emerges is that the commensalCandidaspecies that inhabit the oral cavities of HIV+patients are subjected to a number of significant pressures that probably promote the selection of organisms with unusual phenotypes and genotypes. TheseCandidaare more difficult to characterize and behave differently compared to their counterparts in HIV-individuals. It is clear that uncovering the factors that are important for the selection of treatment regimens and will be predictive of outcome will not be easy.Candidaorganisms are neither as benign nor as simple as once thought.

ISSN:1040-841X    

DOI:10.3109/10408419309113523

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractThis review followed from experiments suggesting that some fungi do not require calcium. It was found that many studies of a calcium requirement in microorganisms had assumed specificity for chelation agents such as EGTA and A23187, which the reagents did not possess. Early studies still cited today often preceded the recognition that microorganisms required manganese and zinc. As a result of both of these misunderstandings, there was rarely any attempt to replace calcium by other important trace elements. In some studies that seem to have been overlooked, the apparent requirement for calcium depended on the growth conditions used.Escherichia coli, Neurospora crassa, andSaccharomyces cerevisiaewere then selected for detailed consideration and it is concluded that further experiments are needed before the involvement of calcium is proved.

ISSN:1040-841X    

DOI:10.3109/10408419309113524

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractAnaerobic zoospore-producing fungi that inhabit the gastrointestinal tract of herbivores, especially ruminants, have recently been discovered. These fungi have been isolated from the rumen, hind gut, and the feces of ruminants. Thirteen species, belonging to five genera, of these fungi have been assigned to the class Chytridiomycetes. These species arc classified according to the number of flagella on the zoospores and the types of thalli that develop from the zoospores. Their life cycle consists of a zoospore that encysts and develops into a vegetative thallus with zoosporangia, which at times become resting sporangia. These fungi produce a wide range of active hydrolytic enzymes, notably cellulases and xylanases, that provide them with the potential to degrade the major structural polysaccharides in plant cell walls. Their cellulases are among the most active reported to date and solubilize both amorphous and highly ordered cellulose. Their esterases are active against both feruloyl and p-coumaroyl arabinoxylans, which provides an advantage in degrading poorly biodegradable cell walls. They degrade lignin-containing cell walls, but do not metabolize the lignin moiety. Rhizoids of vegetative thalli penetrate cell walls, and they are better able than bacteria or protozoa to attack recalcitrant tissues and weaken the textural strength of plant material.

ISSN:1040-841X    

DOI:10.3109/10408419309113525

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor

摘要:

AbstractMany species of bacteria have been found to form fractal colonies. Environmental (physico-chemical) and biological factors for this fractal morphogenesis have been examined for their roles in the genesis of fractal and pattern diversity. Morphology of a bacterial colony on a solid agar medium depends on the nutrient diffusion field (two-dimensional). When concentrations of nutrients are low, point-inoculated bacteria (e.g.,Bacillus subtilis)exert diffusion-limited growth. A self-similar fractal colony formed slowly under such a condition has the same morphology as one made by the diffusion-limited aggregation (DLA) model. The value of fractal dimensions (ca. 1.72) and the appearance of specific phenomena (screening and repulsion effects) are consistent with computer simulations of the DLA fractal model. On the other hand, a round colony recognized on an agar-rich medium was considered to be the product of reaction-limited growth and was simulated by the Eden model. When motile bacteria are point inoculated onto semi-solid agar media, bacterial spreading behavior also is morphogenic. Branching patterns with various morphologies (e.g., dense-branching morphology) have been recognized and examined for factors responsible for pattern changes. By microscopic inspection of the extending branch, multicellular behavior of bacteria has been observed in the structured cell distribution. Besides cell division and translocation activities, wetting agents produced by some species of bacteria (e.g., serrawettins produced bySerratia marcescens)are considered to be important microbial factors for efficient space occupation and specific cell transpositions in various surface environments.

ISSN:1040-841X    

DOI:10.3109/10408419309113526

出版商:Taylor&Francis    

年代:1993

数据来源: Taylor