Colitis. Light micrograph (LM) of a section of bacterial invasion of human gut wall. Colitis is a life-threatening complication of aplastic anaemia which occurs during periods of profound neutropenia (a low neutrophil white blood cell count) which causes variable submucosal necrosis with invasion of the colonic wall by bacteria. (blue stained rods). Magnification: x350 when printed at 10 centimetres wide. Human tissue.