Free-living amoebae promote Candida auris survival and proliferation in water

Candida auris is an emerging species responsible for life-threatening infections. Its ability to be resistant to most systemic antifungal classes and its capacity to persist in a hospital environment have led to health concerns. Currently, data about environmental reservoirs are limited but remain essential in control of C. auris spread. The aim of our study was to explore the interactions between C. auris and two free-living amoeba (FLA) species, Vermamoeba vermiformis and Acanthamoeba castellanii, potentially found in the same water environment. Candida auris was incubated with FLA trophozoites or their culture supernatants. The number of FLA and yeasts was determined at different times and transmission electron microscopy (TEM) was performed. Supernatants of FLAs promoted yeast survival and proliferation. Internalization of viable C. auris within both FLA species was also evidenced by TEM. A water environmental reservoir of C. auris can therefore be considered through FLAs and contamination of the hospital water networks would consequently be possible.     

Biotyping of pathogenic fungi by the killer system and with monoclonal antibodies

Biotyping of pathogenic yeasts and hyphomycetes based on their suceptibility to selected killer yeasts and their reactivity with monoclonal antibodies are described. Both methods were used to differentiate fungi isolated from patients providing valuable epidemiological information on mycotic infections. The functional biotyping obtained with the two systems and the conventional auxenographic biocoding approaches commercially available for opportunistic yeasts are comparatively evaluated. The potential for biotyping of industrial fungal isolates is also discussed.     

Enumeration and presumptive identification of some functional groups of bacteria in the rumen of dairy cows fed grass silage-based diets

Abstract Samples of rumen ingesta from two rumen-fistulated dairy cows fed grass silage-based diets were examined for numbers and types of bacteria that developed colonies on rumen fluid-agar media designated to support the growth of (a) a wide range of species, (b) cellulolytic bacteria, (c) lactate-fermenting bacteria, (d) non-fermentative bacteria. The most numerous species was Bacteroides ruminicola followed by Butyrivibrio fibrisolvens . The most abundant cellulolytic species were Eubacterium cellulosolvens and Ruminococcus flavefaciens. Megasphaera elsdenii and Selenomonas ruminantium were important lactate fermenters but an unidentified bacterium that grew poorly on maintenance medium was by far the most numerous among bacteria isolated from lactate-containing medium. One strain remained sufficiently viable to show that it fermented lactate to propionate and acetate.     

Formation and physiological role of biosurfactants produced by hydrocarbon-utilizing microorganisms

Microbial growth on water-insoluble carbon sources such as hydrocarbons is accompanied by metabolic and structural alterations of the cell. The appearance of surface-active compounds (biosurfactants) in the culture medium or attached to the cell boundaries is often regarded as a prerequisite for initial interactions of hydrocarbons with the microbial cell. Under this point of view, biosurfactants produced by hydrocarbon-utilizing microorganisms, their structures and physico-chemical properties are reviewed. The production of such compounds is mostly connected with growth limitation in the late logarithmic and the stationary growth phase, in which specific enzymes are induced or derepressed. Addition of purified biosurfactants to microbial cultures resulted in inhibitory as well as in stimulatory effects on growth. Therefore, a more differentiated view of microbial production of surface-active compounds is proposed. Biosurfactants should not only be regarded as prerequisites of hydrocarbon uptake, but also as secondary metabolic products.     

Constitutive appearance of peroxisomes in a regulatory mutant of the methylotrophic yeast Hansenula polymorpha

Summary A selection by glucosamine for mutants of Hansenula polymorpha insensitive to glucose repression of methanol assimilation is described. Constitutive synthesis of enzymes is established in standard batch cultures of glucosegrown cells. Upon prolonged glucose metabolism the phenotype is masked by catabolite inactivation and degradation of enzymes. Addition of the substrate methanol remarkably improves constitutive synthesis by preventing catabolite inactivation and delaying degradation. Regular peroxisomes of reduced number are formed in mutant cells under repressed conditions. No constitutive synthesis is detectable using ethanol as a carbon source. In addition, this alcohol is detrimental to growth of the mutants, indicating that H. polymorpha is constrained to repress synthesis of enzymes involved in the C₁-metabolism when ethanol is present as a substrate.     

The vectoring of cactophilic yeasts by Drosophila

Summary At two locations in the Sonoran Desert, yeasts were sampled from species of Drosophila, the flies' cactus hosts, and other neighboring sources of cactophilic yeasts to determine the relation between the yeasts vectored by the fly and the yeasts found in their breeding sites. D. mojavensis, D. nigrospiracula, and D. mettleri vectored yeast assemblages significantly more similar to the yeast species found on the rot from which the flies were collected than to the yeasts found on other rots from the flies host cactus or other rotting cactus at the same site. Rots with Drosophila had fewer yeast species than those without flies, suggesting that flies were associated with younger rots. Rots with flies and the Drosophila also had more yeast species with the capability to produce ethyl acetate than rots without flies. The results support the contention that cactophilic Drosophila feed on a subset of the yeasts available in an area, and may act to maintain differences among the yeast communities found on different species of cactus.     

Neotypification of the genusTrichosporon

The currently accepted type species of the genusTrichosporon Behrend isT. beigelii. This species has formerly been regarded as identical toT. cutaneum. However, these fungi are now known to represent separate species with different ecology. The first species described inTrichosporon wasT. ovoides, an agent of human white piedra. A neotype strain is designated for this species, while a lectotype strain is indicated forT. cutaneum. The nameT. beigelii is considered as doubtful and consequently cannot be maintained.     

CUG codons inCandida spp.

Codon CUG is used for serine instead of for leucine, its usual assignment, in several yeasts of the genusCandida. We propose a series of steps for the reassignment, including disappearance of leucine CUG and its anticodon CAG, formation of a new serine tRNA, with anticodon CAG, from a duplication of the gene for serine tRNA (IGA), and then production of CUG codons by mutation at sites that are mostly nonessential.     

Ecology of Microbial Saprophytes and Pathogens in Tissue Culture and Field-Grown Plants: Reasons for Contamination Problems In Vitro

This review compares published surveys of microbial populations in plant tissue and cell cultures with the microbial saprophytes and pathogens found on field grown plants and microbial populations in the laboratory environment. From this comparison and the measured reduction in contamination after improvements in working practices in the laboratory, conclusions can be drawn about the importance of the explant and the laboratory as sources of contamination.

Mechanisms of pathogenicity in vitro are described to explain why bacteria, fungi, and yeasts that are not pathogenic to plants in the field become pathogens in plant tissue cultures. Conversely, plant metabolism and its effect on the tissue culture environment are described to explain why prokaryotes, viruses, and viroids that cause disease in the field can stay latent in vitro.

Detection methods for latent contaminants in plant tissue cultures are summarized, and the strategies and methods for prevention or treatment of contamination are discussed.