Step 1 Create a new document, press D for default colors. Click on the Channels window and create a new channel with the create new channel button at the bottom of the screen. Then go to filter>render>clouds.
Step 2 Go to filter>stylize>glowing edges and use settings in the neighborhood of 12/17/14. Just make sure it's not too bright.
Step 3 ctrl-click the channel so that it makes a selection, click back on the layers window, and create a new layer. Press ctrl-backspace to fill the selection with white. This is the bacteria layer. Go ahead and make a new layer underneath the bacteria layer and fill it with black so we have a background.
Step 4 Go into the blending mode of the bacteria layer and choose color overlay. Choose whatever color you like and set the opacity around 70%.
Step 5 Now in the blending mode set a pattern overlay and choose Metal Landscape (it's a default Photoshop pattern). Set the opacity to around 50%. It should look something like bacteria now.
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