Localization of active microorganisms in cheese by autoradiography

By using an autoradiographic technique, one can follow, during ripening of a cheese, the distribution, size, and metabolic activity of microcolonies. Fragments of cheese were labeled with [H]leucine, fixed, and mounted in epoxy resin. After exposure and development, sections were examined by optical microscopy. In Camembert cheese, bacterial microcolonies synthesized protein rapidly during the beginning of the ripening process. At the end of the ripening process, active bacterial clusters were scarcer and of two types: (i) large microcolonies with reduced labeling, and (ii) microcolonies having the same size as those observed at the beginning of the ripening process, but with slight or no labeling.