FIG. 1.

Transmission electron microscopy of M. tuberculosis stained with ruthenium red to demonstrate the capsule. The bacteria had been syringed (A and B) or sonicated in three 30-s bursts (C) prior to processing. (A) The cell wall envelope is shown and consists of the plasma membrane and peptidoglycan layers (thin white arrow), an electron-transparent region (large white arrowhead) representing the mycolic acids, glycolipids, and other lipid polymers, and a thick capsule-like outer layer stained strongly by the ruthenium red (blackarrowheads). (B) Syringed bacteria exhibit a capsule of uniform thickness and distribution among the population. (C) Following sonication, the capsule appears to have extended and is unevenly distributed, both around each individual bacteria and between individuals in the population. However, the integrity of the bacterial cells otherwise appears to be comparable to that of the syringed bacteria in B. Bars: 100 nm (A) and 500 nm (B and C).