Bacterial infection of bladder (cystitis). Colour Scanning Electron Micrograph (SEM) of the human bladder showing bacterial infection. Rod-shaped Escherichia coli bacteria (yellow) are seen on swollen epithelial cells (blue) of the bladder. The infection has progressed to a haemorrhagic state causing bleeding, with red blood cells seen at left. The epithelial surface has secreted thick mucus filaments (orange). Bladder infection or cystitis is commonly due to E.coli, causing pain in passing urine and inflammation. It affects more women because the urethra is short and easily infected. Magnification: x810 at 6x7cm size. Magnification: x1,200 at 4x5 inch size.