Intestinal bacteria

Segmented filamentous bacteria (SFBs) embedded in the epithelium of a rat Peyer's patch. Peyer's patches are regions of lymphoid tissue in the intestine of all mammals. These bacteria attach firmly to the brush border of the epithelial cells using a specialised structure that forms an indentation within, but does not penetrate, the plasma membrane. Similar unclassified microorganisms are present in all mammals examined.