An Electron Microscope Study of the Mesosomes of a Penicillinase-producing Staphylococcus

SUMMARY Thin sections of Staphylococcus aureus were examined in the electron microscope, before and after treatments which released part of their cell-bound penicillinase. In all cases, such treatment resulted in alteration of the mesosome structure: the mesosome was replaced by a series of pockets or invaginations in the cytoplasmic membrane. The converse situation was not always true; cocci treated in such a way as to alter the mesosome structure did not necessarily release penicillinase. This leads to the conclusion that structural alteration of the mesosome is only one of a number of steps in the release of penicillinase.