Direct observation of fine structures of bacteria in ripened Cheddar cheese by electron microscopy.

Abstract

This investigation was undertaken to clarify ultrastructure of Cheddar cheese texture and morphological changes in lactic acid bacteria firmly embedded in cheese. Fine structures of Cheddar cheese ripened for 5 months, sliced into ultra-thin sections were observed with an electron microscope. Cheese bacteria were often found crowded around larger fat globules in limited regions of cheese. Shapes of living cells were short and rod-like. Cell walls, cross-wall sections and several organelles were distinctly observed in living cells. Intact cells were recognized to be clearly differentiated from dead cells by morphological changes. The occurrence of cell wall lysis characterized dead cells, and segments of cell walls were released from cells and curled nearly after lysis. Unit membranes of protoplast were also maintained without bursting. Moreover, protrusion of cell contents from protoplasts was also found in the cells from which parts of cell wall had been released.