Ruthenium red and the bacterial glycocalyx.

Ruthenium red, a promising cationic reagent for electron microscopy (EM), has long been an important tool in histology. The reagent was initially used by botanists as a semispecific stain for pectic substances, but it has gradually been embraced by investigators in microbiology and the animal sciences as a stain for anionic glycosylated polymeric substances. Luft developed a reliable method and demonstrated that ruthenium red was a useful reagent for visualizing ultrastructural detail. Many investigators, using modifications of Luft's approach, have identified numerous applications for this important reagent. Ruthenium red has been used to show the ultrastructural detail of bacterial glycocalyces. Strong, sharp and consistent observations of this ultrastructural component of the bacterial cell have given a better understanding its fibrous anionic matrix. Any variations in staining owing to artifactual alteration of the fine delicate ultrastructural features have been overcome by incorporation of diamine lysine into ruthenium red methods, thus providing flexible processing times under less than ideal laboratory sampling conditions. Ruthenium red has broad utility in the biological sciences, and in combination with lysine, it is an excellent EM stain for enhanced visualization of bacterial glycocalyx from culture or from clinical specimens.

Analysis of fluconazole effect on Candida albicans viability during extended incubations.

Fluconazole is an azole agent with primarily fungistatic activity in standard in vitro susceptibility tests. However, recent work has demonstrated that this drug can reduce Candida albicans viability during prolonged incubations under non-growing conditions. The present study was undertaken to examine more closely some of the parameters of this killing activity. Fungicidal effects of 1.0 microg ml-1 of fluconazole were found during 7-14-day exposures in each of two media that prevented proliferation, distilled water and metal-depleted RPMI 1640 tissue-culture medium. Fluconazole appeared to be stable after being incubated at 37 degreesC for either 7 or 14 days. Strains of C. albicans resistant to fluconazole in standard short-term growth-inhibition assays were also found to be resistant to fluconazole's effect on viability in prolonged culture, suggesting similar mechanisms of action for these effects. C. albicans yeast cells pre-incubated for 7 days in distilled water were not more sensitive to the drug in short-term susceptibility assays. Although all proliferation of the organisms in distilled water cultures appeared to cease after 3 days, fluconazole added at 7 days still reduced C. albicans viability. Therefore, the drug appeared to kill the non-proliferating organisms directly rather than preventing growth and thereby the emergence of younger organisms that would live longer. Transmission electron microscopy demonstrated damage to the cell wall-cell membrane complex and interior contents of yeast cells incubated in distilled water alone; fluconazole appeared to increase the percentages of cells so affected. In summary, extended-incubation susceptibility tests demonstrated that fluconazole has direct fungicidal activity of non-proliferating C. albicans yeast cells. These results may be relevant to the manner in which this drug promotes clearance of chronic fungal infections.

Ruthenium red preserves glycoprotein peplomers of C-type retroviruses for transmission electron microscopy.

Peplomers, the glycoprotein projections of the outer viral envelope, are distinctive for many viruses. Peplomers of retroviral C-type particles are fragile and are not preserved in standard preparations for transmission electron microscopy of thin sections, whereas the peplomers of B- and D- type retroviruses are usually preserved. Ruthenium red, extensively used in transmission electron microscopy to enhance the preservation of glycosylated proteins, was used in the preparation of three retrovirus-producing lymphoblastoid cell lines: murine SC-1 cells producing the C-type murine leukemia retrovirus LP-BM5 that causes immunodeficiency, human DG-75 cells producing a murine leukemia retrovirus, and human C5/MJ cells producing human T-cell lymphotropic virus type I (HTLV-I). Fixation of cells was carried out with ruthenium red present in the glutaraldehyde, osmium tetroxide, and the ethanol dehydration through the 70% ethanol step. The detailed structure of peplomers of these three different viruses was well preserved.

Superior preservation of the staphylococcal glycocalyx with aldehyde-ruthenium red and select lysine salts using extended fixation times.

The utility of lysine-based aldehyde-ruthenium red fixatives for the preservation and/or staining of the fibrous staphylococcal glycocalyx was improved by substitution of alternative forms of lysine for the free amino form. Paraformaldehyde-glutaraldehyde fixatives containing alternative lysines, with or without ruthenium red, were compared at short 20-minute prefixation times and at extended overnight fixation times. Although inclusion of paraformaldehyde made longer fixation times possible, the length of time for "safe" fixation varied per sample and could not be predicted. All alternative lysine forms permitted fixation of at least 24 hours without sample loss. The L-lysine monohydrochloride or L-lysine acetate forms permitted longer fixation times than the L-lysine free amino form, and they had comparable or better preservation of the staphylococcal glycocalyx. Thus, the usefulness of aldehyde-lysine-based fixatives with minor changes has been enhanced.

The use of dimethylsulfoxide for fixation of yeasts for electron microscopy.

Conventional methods of chemical fixation are often inadequate for preserving yeast ultrastructure. The thick cell wall severely limits penetration of fixatives rendering poor detail of the cell wall, membranes, and overall anatomy. Dimethylsulfoxide (DMSO) enhances penetration of chemicals and has been added to fixatives to improve cell preservation. At high concentrations (5 to 50%), however, it affects ultrastructure unpredictably. We found that adding 0.1% DMSO to fixatives greatly improved retention of yeast ultrastructure. Candida albicans, C. glabrata and Aspergillus fumigatus were fixed for 3 hr in 3% paraformaldehyde, 1% glutaraldehyde, 1 mM MgCl2, 1 mM CaCl2, 0.1% DMSO in 0.1 M sodium cacodylate buffer followed by 1% OsO4, 1% K2Cr2O7, 0.85% NaCl, 0.1% DMSO in the same buffer. Thin epoxy sections were post-stained in uranyl acetate and lead citrate. The multilayered character of the cell wall was distinct and well structured. Addition of ruthenium red or alcian blue to the fixatives further enhanced the outer fibrillar layer. The plasma membrane was contiguous and tightly adjacent to the inner mannoprotein layer of the cell wall. The cytoplasm was well preserved and the overall preservation of the yeast ultrastructure was significantly improved.

Paraformaldehyde effect on ruthenium red and lysine preservation and staining of the staphylococcal glycocalyx.

The utility of lysine in glutaraldehyde-ruthenium red fixatives for the preservation and/or staining of the fibrous staphylococci glycocalyx was improved by inclusion of paraformaldehyde. Short, 20 min prefixation times for paraformaldehyde-glutaraldehyde fixatives containing lysine, with or without ruthenium red, were compared to an extended overnight fixation. Samples were often lost in fixatives that did not contain paraformaldehyde at extended fixation times hampering the effective use of these fixatives for clinical or environmental applications. Inclusion of paraformaldehyde in the fixation with lysine permitted longer fixation times as well as stabilized the staphylococcal glycocalyx. Thus, the technical usefulness of fixatives employing lysine was significantly improved.

A double fluorescence staining protocol to determine the cross-sectional area of myofibers using image analysis.

A double fluorescence staining protocol was developed to facilitate computer based image analysis. Myofibers from experimentally treated (irradiated) and control growing turkey skeletal muscle were labeled with the anti-myosin antibody MF-20 and detected using fluorescein-5-isothiocyanate (FITC). Extracellular material was stained with concanavalin A (ConA)-Texas red. The cross-sectional area of the myofibers was determined by calculating the number of pixels (0.83 mu m(2)) overlying each myofiber after subtracting the ConA-Texas red image from the MF-20-FITC image for each region of interest. As expected, myofibers in the irradiated muscle were smaller (P < 0.05) than those in the non-irradiated muscle. This double fluorescence staining protocol combined with image analysis is accurate and less labor-intensive than classical procedures for determining the cross-sectional area of myofibers.

Localization of methanol dehydrogenase in two strains of methylotrophic bacteria detected by immunogold labeling.

Antibodies to methanol dehydrogenase purified from Methylobacterium sp. strain AM1 and Methylomonas sp. strain A4 were raised. The antibody preparations were used in indirect immunogold labeling studies. With this approach, methanol dehydrogenase was found to be preferentially localized to the periplasmic region of the methylotroph Methylobacterium sp. strain AM1 and to the intracytoplasmic membrane of the methanotroph Methylomonas sp. strain A4. Antibody cross-reactivity to other methylotrophic bacteria was detected.

Comparison of alcian blue and ruthenium red effects on preservation of outer envelope ultrastructure in methanotrophic bacteria.

Alcian blue (AB) and ruthenium red (RR) effects on ultrastructural preservation of the bacterial cell envelope of methanotrophs are compared. A previous successful method with RR that enhanced preservation of outer envelope layers in two representative methanotroph species is applied to other genera and species of methanotropic bacteria. Alcian blue is substituted for RR in this en bloc protocol. The effect of AB on preservation of these layers is assessed at the ultrastructural level and compared to RR for all species examined. Further, comparison with freeze etch and a fixation in the absence of either RR or AB is made. Both RR and AB are found to aid preservation and help visualize additional components of the cell envelope which are lost or minimized in a standard fixation not employing these cationic reagents. For some species, images obtained are similar between RR and AB procedures and agree with images seen by freeze etch. For other species, AB preserves extended filamentous material that is partially condensed even with the use of RR. Thus, use of AB improves the preservation of outer envelope structure in these organisms equally or more effectively than use of RR.

Effects of retinyl acetate on surface morphology and intramembrane particle distribution in the plasma membrane of 10T1/2 cells.

Scanning electron microscopy and freeze fracture electron microscopy were used to characterize membrane ultrastructural differences between parental, C3H/10T1/2, and carcinogen-initiated, INIT C3H/10T1/2, cells and treatments with retinyl acetate. The intramembranous particle distribution on the E-face was detected and quantitated by the methods of automated image analysis to obtain statistically meaningful numerical characteristics of intramembranous particle size and density. Subtle differences were found when no differences were apparent by light microscopy or by scanning electron microscopy. Initial retinyl acetate treatment caused a significant increase of the intramembranous particle size in parental cells. Intramembranous particle density increased for retinyl acetate treatment in parental and INIT cells and in INIT cells previously maintained but withheld from retinyl acetate. Intramembranous particle distribution analysis includes the interparticle distance of nearest neighbors and the randomness of the distribution by the differential density distribution function, which compares the observed sample to Poisson modified for particle size. These measures show that the three cell groups that have been treated with retinyl acetate have a more even distribution of intramembranous particles than was found for untreated parental cells. The relationship between the freeze fracture morphology and the biological responses to retinyl acetate treatment is discussed.

Effect of fixation-resin combinations and ruthenium red on elucidating outer envelope structure and surface morphology of two methanotrophic bacteria.

We examined the ultrastructure of the cell envelope in Type I, Methylomonas albus (BG8), and Type II, Methylosinus trichosporium (OB3b), methane-oxidizing bacteria by using different fixatives, ruthenium red (RR) combinations and resins. We compared LR White and Spurr embedments with the following fixations: glutaraldehyde/OsO4, two glutaraldehyde-paraformaldehyde, and two different en bloc ruthenium red procedures, one utilizing OsO4 and the other with glutaraldehyde/OsO4 in sequential fixation. These fixations were also studied by scanning electron microscopy (SEM). Unfixed cells prepared by freeze etch were used for comparison. Transmission electron microscopy of BG8 embedded in LR White resin (with or without red0 preserved a layer of cup-like structures that were not seen in Spurr resin-embedded cells unless ruthenium red was used. For OB3b, the second RR method preserved beads and filaments where only "spike-like" structures were seen in all other fixations in both resins. By SEM, all fixations preserved a capsular slime layer of BG8 that was removed from some cells by both RR methods. In all SEM fixations, a bead layer was preserved in OB3b that was enhanced by RR. Filaments seen by freeze-etch and thin-section techniques were not seen in SEM. Presence or absence of particular envelope structures in these methanotrophs is dependent on the combination of fixatives and/or resins employed and is species-specific. The chemical preparation methods used resulted in enhanced understanding of the structure and composition of the cell envelope.

Electron microscopic study of the calcium phosphate-induced aggregation and membrane destabilization of cytoskeleton-free erythrocyte vesicles.

Cytoskeleton-free vesicles derived from human erythrocytes were treated with trypsin, chymotrypsin, or neuraminidase followed by calcium, phosphate, or combined calcium/phosphate treatments in order to study the roles of cell surface proteins and glycoproteins in calcium/phosphate-induced cell aggregation and fusion. Vesicle aggregation (a necessary pre-cursor to membrane fusion) and subsequent membrane destabilization (an essential component of fusion) were examined by freeze-fracture electron microscopy. Enzymatic treatment alone had no effect on the morphology of the cytoskeleton-free vesicles. Neither did separate calcium nor phosphate treatments, although the treatment of the cytoskeleton-free vesicles with calcium did reduce their size slightly. Enzymatic pretreatment had no effect on the calcium-induced size changes. In contrast, the combination of calcium and phosphate drastically disrupted the membrane integrity of aggregated cytoskeleton-free vesicles at pH 7.8, although the effect was reduced at lower pH values. The extent of this membrane destabilization was independent of enzyme treatment. Our results indicate: (1) that the cell surface proteins and glycoproteins have only secondary effects on calcium/phosphate-induced cell aggregation and membrane destabilization, (2) that these processes primarily depend on the reaction between calcium and phosphate ions at the membrane surface, and (3) that cytoskeletal elements probably play no active (positive) role in the Ca2+/PO4(3-) induced erythrocyte membrane fusion process, apart from maintaining cell shape.

Quantitative analysis of intramembranous particles in rapidly frozen 10T1/2 cell monolayers.

A simple method for ultrarapid freezing of cell cultures in monolayers was developed. Unfixed and unglycerinated cells were grown on glass substrates. No special treatments of the glass or cells were necessary to facilitate freeze-fracture along the upper plasma membranes. A reliable nonbiased method was developed to detect intramembranous particles (IMP) from the background by totally automatic means using the Cambridge Instruments Quantimet 920 Image Analysis system. Size and density data of IMP from a large number of electron micrographs can be rapidly and objectively quantitated. The automatic determination of locational coordinates for each IMP enables subtle determination of spatial distributional differences by the nearest neighbour function and the differential density distribution function, which are measurements of randomness. Quantitative analysis of the IMP distribution on the fracture face of C3H/10T1/2 mouse embryo fibroblasts upon various drug treatments was demonstrated.