A set of samples was investigated under the light microscope (Primo Star, Zeiss, equipped with Axio Cam 105 color) without prior sample treatment. For fluorescence microscopy of living and dead cells, samples were washed twice with PBS containing 10 wt% NaCl. Three milliliters of each sample was stained with 3 μL of a 1:2 mixture of component A (SYTO 9 dye, 3.34 mM) and component B (propidium iodide, 20 mM) from the Invitrogen Live/Dead BacLight Bacterial Viability Kit, where component A causes green fluorescence of intact cells and component B causes red or orange fluorescence of dead cells with damaged cell walls. The stained samples were imaged with a fluorescence microscope (Polyvar 2, Reichert-Jung) equipped with a Xenon lamp (XBO 150 W/1).
Samples for scanning electron microscopy (SEM) were washed twice with PBS containing 10 wt% NaCl followed by fixation in 2.5% glutaraldehyde solution (in 0.1 M phosphate buffer [PB], pH = 7.3). The fixed samples were washed twice with 0.1 M PB, dehydrated through a graded acetone series (50%, 70%, 90%, 95%, 100%), critical point dried in a Leica CPD300, coated with carbon, and imaged with a Hitachi S-2700 microscope.
Samples for scanning electron microscopy (SEM) were washed twice with PBS containing 10 wt% NaCl followed by fixation in 2.5% glutaraldehyde solution (in 0.1 M phosphate buffer [PB], pH = 7.3). The fixed samples were washed twice with 0.1 M PB, dehydrated through a graded acetone series (50%, 70%, 90%, 95%, 100%), critical point dried in a Leica CPD300, coated with carbon, and imaged with a Hitachi S-2700 microscope.