Mesosome

Mesosomes or chondrioids are folded invaginations in the plasma membrane of bacteria that are produced by the chemical fixation techniques used to prepare samples for electron microscopy.

These structures are invaginations of the plasma membrane observed in gram-positive bacteria that have been chemically fixed to prepare them for electron microscopy.

[2][7][8] By the mid to late 1980s, with advances in cryofixation and freeze substitution methods for electron microscopy, it was generally concluded that mesosomes do not exist in living cells.

[12][13] Recently, similar folds in the membrane have been observed in bacteria that have been exposed to some classes of antibiotics,[14] and antibacterial peptides (defensins).

[15] The appearance of these mesosome-like structures may be the result of these chemicals damaging the plasma membrane and/or cell wall.