Bacterial capsules. Light micrograph of unidentified bacteria (blue) encased in capsules (pink). Each capsule or slime layer (glycocalyx) is a thick layer of slimy material secreted by the bacteria onto their surfaces. They can help the bacteria to attach onto the host cells they are infecting. They may also serve to protect the bacteria from immune cells such as phagocytes. Phase contrast. Magnification: x1000 at 35 mm size.