Aug 30, 2020
Commander Rory: Here we have a capsule stain, it is useful in trying to identify organisms through virulence factors, things that aid in causing a disease. The capsule is the white halo you see around those pink dots, which are the bacterial organisms. Capsules are a polysaccharide layer used to help protect the bacteria from harm such as preventing phagocytosis, or digestion of the bacteria, by white blood cells like macrophages.
You can tell there is a good chance the organism has a capsule if it looks and feels like it has a mucous-y texture on media plates such as blood agar or trypticase soy agar. A common organism identified with a capsule is Klebsiella pneumoniae which is one organism that can cause pneumonia.