The ability to produce a capsule is an inherited property of the organism, but the capsule is not an absolutely essential cellular component. Capsules are often produced only under specific growth conditions. Even though not essential for life, capsules p robably help bacteria to survive in nature. Capsules help many pathogenic and normal flora bacteria to initially resist phagocytosis by the host's phagocytic cells. In soil and water, capsules help prevent bacteria from being engulfed by protozoans.
Capsules also help many bacteria to adhere to surfaces and thus resist flushing.
The skim milk supplies essential nutrients for capsule production and also provides a slightly stainable background. Stir up the Skim Milk broth culture with your loop and place 2-3 loops of Enterobacter aerogenes on a slide. Using your loop, spread it out over the entire slide to form a thin film. Let it completely air dry. Do not heat fix .