Fimbriae (also called pili), polar filaments radiating from the surface of the bacterium to a length of 0.5-1.5 micrometers and numbering 100-300 per cell, enable bacteria to colonize the epithelium of specific host organs. K88 fimbria, 0.1-1 micrometer in length and 7 nanometers in diameter, is composed of about 100 identical subunits. Predominantly located at the tip of the fimbriae.