At a very high magnification of 90,000X, this transmission electron microscopic (TEM) image revealed some of the ultrastructural morphology exhibited by numbers of Legionella pneumophila bacteria, which had been grown on a bacteriologic medium. This specimen was prepared using the osmium fixation method. Of importance, is that these organisms are encased in a double envelope consisting of inner and outer, triple layered, unit membranes. Also, note that there are vacuoles present within some of the bacteria. L. pneumophila is responsible for causing the pneumonic disease known as Legionnaires’ disease.