Escherichia coli. Coloured Transmission Electron Micrograph (negative stain) of Escherichia coli bacteria. E. coli are Gram-negative rod-shaped bacilli. Those seen here possess long hair-like flagella, enabling motility and a capsule (brown). E. coli occur normally in the gut flora of humans and warm-blooded animals. Some strains are pathogenic. These bacteria were isolated from a newborn baby with meningitis (infection of the membranes enclosing the brain and spinal cord). They possess an acidic polysaccharide in the capsule which is a known virulence factor found in E. coli strains causing purulent meningitis. Magnification: x9, 300 at 6x7cm size.