Tools: Zbrush, 3ds max, Vray, Photoshop.

1- I fast-sculpted the microbe mesh inside Zbrush.

microbes-view-grab-1
2- Then, inside 3ds max, I scattered it using PFlow.

microbes_view_grab_2
3- One simple shader (Leagacy Fallof)

microscopic-shader
4- … And one Vray Light source (on the right of the camera).
After rendering the image, I made some tweakings using Photoshop.

cg-microbes-2
microbes_view_grab_2