The development of mesosomes of Staphylococcus aureus during autolysis.

Mesosomes of Staphylococcus aureus were examined morphologically under the electron microscope. Three different methods of specimen preparation (thin section, freeze-fracture, and negative staining) were used to eliminate artifacts due to sample processing. Mesosomes were rarely seen in intact cells but were quite distinct in autolysed cells incubated in 1.2M sucrose -0.33M acetate buffer (pH 5.8) at 25 degrees C. The phospholipid content increased by 20% of the control as autolysis proceeded. Since the plasma membrane did not show any other significant changes, the development of mesosomes during autolysis was shown to be a real event. Most of the well-developed mesosomes were found at the septum in negatively stained specimens. Initial wall-lysis occurred at this site, suggesting a close relationship between autolysis and the development of mesosomes in S. aureus.