False colour transmission electron micrograph (shadow technique) of Klebsiella pneumoniae, a rodlike bacterium associated with pneumonia & other respiratory infections in humans. Most Klebsiella species live harmlessly in the human respiratory, intestinal & urinogenital tracts. Other species are pathogenic. The hairlike structures fringing certain bacteria at certain times are called pili. There are several types of pili serving different functions; the best studied are the sex pili involved in the transfer of DNA from donor to receipent cells during conjugation. This cell is undergoing division (binary fission). Mag: X 17,650 (at 35mm size).