Enumerative fluorescent vital staining of live and dead pathogenic yeast cells

Kinetics of biofilm formation by drinking water isolated Penicillium expansum

Current knowledge on drinking water (DW) biofilms has been obtained mainly from studies on bacterial biofilms. Very few reports on filamentous fungi (ff) biofilms are available, although they can contribute to the reduction in DW quality. This study aimed to assess the dynamics of biofilm formation by Penicillium expansum using microtiter plates under static conditions, mimicking water flow behaviour in stagnant regions of drinking water distribution systems. Biofilms were analysed in terms of biomass (crystal violet staining), metabolic activity (resazurin, fluorescein diacetate and 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide [MTT]) and morphology (epifluorescence [calcofluor white M2R, FUN-1, FDA and acridine orange] and bright-field microscopies). Biofilm development over time showed the typical sigmoidal curve with noticeable different phases in biofilm formation (induction, exponential, stationary, and sloughing off). The methods used to assess metabolic activity provided similar results. The microscope analysis allowed identification of the involvement of conidia in initial adhesion (4 h), germlings (8 h), initial monolayers (12 h), a monolayer of intertwined hyphae (24 h), mycelial development, hyphal layering and bundling, and development of the mature biofilms (≥48 h). P. expansum grows as a complex, multicellular biofilm in 48 h. The metabolic activity and biomass of the fungal biofilms were shown to increase over time and a correlation between metabolism, biofilm mass and hyphal development was found.

Development of the FUN-1 family of fluorescent probes for vacuole labeling and viability testing of yeasts

A new family of fluorescent probes has been developed for assessing the viability and metabolic activity of yeasts. This class of halogenated unsymmetric cyanine dyes is exemplified by the FUN-1 [2-chloro-4-(2,3-dihydro-3-methyl-(benzo-1,3-thiazol-2-yl)- methylidene)-1-phenylquinolinium iodide] stain, a membrane-permeant nucleic acid-binding dye that has been found to give rise to cylindrical intravacuolar structures (CIVS) in Saccharomyces cerevisiae. Biochemical processing of the dye by active yeasts yielded CIVS that were markedly red shifted in fluorescence emission and therefore spectrally distinct from the nucleic acid-bound form of the dye. The formation of CIVS occurred under both aerobic and anaerobic conditions and was highly temperature dependent. Treatment of yeasts with the nonmetabolizable glucose analog 2-deoxy-D-glucose reduced cellular ATP levels approximately 6-fold and completely inhibited CIVS formation. Under aerobic conditions, the formation of CIVS was abrogated by the cytochrome oxidase inhibitors azide and cyanide; however, the H+ transport uncoupler carbonyl cyanide m-chlorophenylhydrazone inhibited CIVS formation under both aerobic and anaerobic conditions. Depletion of cellular thiols, including glutathione, with millimolar concentrations of N-ethylmaleimide, iodoacetamide, or allyl alcohol completely inhibited CIVS production. Marked reduction in the formation of CIVS by ethacrynic acid and sulfobromophthalein, inhibitors of glutathione S-transferase, suggested that dye processing can involve enzyme-mediated formation of glutathione conjugates. The conversion of FUN-1 by S. cerevisiae was studied quantitatively by using several techniques, including fluorometry, flow cytometry, and wide-field and confocal laser scanning fluorescence microscopy.

Evidence that the insulin resistance of pregnancy may not involve a post-receptor defect in human adipocytes

Insulin binding and the capacity of insulin to stimulate the conversion of glucose to carbon dioxide and lipid, and to activate the protein tyrosine kinase associated with the insulin receptor have been investigated in adipocytes isolated from pregnant and non-pregnant women. Insulin binding and the conversion of glucose to lipid were the same for both groups. However, conversion of glucose to CO2 was higher in the non-pregnant group due to an elevated basal activity, and the increase produced by insulin was similar in both groups. The tyrosine kinase activity of the isolated receptor preparations was higher in the pregnant group due to an increase in the basal non-insulin dependent activity, and the increase produced by insulin was similar in both groups. These findings show the in vitro insulin responsiveness of isolated adipocytes is similar for both groups, and suggests that the in vivo insulin resistance of late pregnancy, as far as adipose tissue is concerned, is not due to any inherent defect in insulin action at the receptor or post-receptor level. In vivo insulin resistance may result from an increased level of circulating insulin antagonists.

Use of the direct epifluorescent filter technique for the enumeration of yeasts

The ability of the direct epifluorescent filter technique (DEFT) to enumerate the viable numbers of various species of yeasts was evaluated. A DEFT count could be made in less than 10 min and the DEFT counts of non-heat-treated samples agreed well with plate counts. The DEFT was unsuitable for the enumeration of yeasts in heat-treated samples because non-viable cells fluoresced orange. A double staining technique using Janus Green B and acridine orange was developed to overcome this problem. The modified DEFT enabled viable and non-viable yeasts to be differentiated in heat-treated samples of pure cultures and improved the relationship between the DEFT count and plate count. The method proved to be of little value, however, for use with beverage products because of unreliable staining patterns.

Studies on plating efficiency and estimation of viability of suspensions of Paracoccidioides brasiliensis yeast cells

Mild sonication was used to obtain single cell suspensions of Paracoccidioides brasiliensis. These cells were intact by microscopic criteria. Direct cell counts in a given inoculum and colony formation on various media were used to determine plating efficiency. Sonicated and nonsonicated cell suspensions were used to study plating efficiency and to estimated viability by means of vital dyes. Methylene blue Erythrosin B, and Janus green were unreliable when used with P. brasiliensis, but vital dyes were accurate when tested with Candida albicans. Acridine orange gave more meaningful results of viability. Estimates of viability, however, changed significantly as a result of relatively minor alterations in the composition of the suspending medium. In initial experiments, the plating efficiency of P. brasiliensis was dismally low. It descended abruptly with increasing dilution of inoculum. Efficiency was much improved if horse serum was added to brain heart infusion plates or if glucose glycine yeast extract (GGY) plates were incubated at room temperature and mycelial colonies were counted. With the technique we report, current plating efficiency of sonicated suspensions is of the order of 25%. Our results and procedures have an important bearing upon those studies concerned with in vitro killing of P. brasiliensis in suspensions or with isolating this fungus from clinical or environmental specimens.

An effective medium for the selective growth of yeast or mycelial forms of Candida albicans: biochemical aspects of the two forms

A new synthetic medium, based on a modification of a commercially available tissue culture medium, allows Candida albicans to be grown in the yeast or mycelial form. Salient features of the system are described and comparisons with previous physiological investigations are discussed. A concise biochemical profile of these two forms of C. albicans is also presented. The results indicate vast metabolic differences between the two forms.