Cytochemical observations on the extracellular carbohydrate produced byStreptococcus cremoris

Abstract

SummaryElectron microscopy showed that a varying proportion of cells ofStreptococcus cremorisNCDO 924 grown in autoclaved skim-milk possessed a layer of extracellular material attached to the cell wall. Occasional filamentous extensions of this layer made contact with neighbouring casein micelles. The same surfacestaining material persisted during the production of cheese-curd, but after maximum scald it was predominantly filamentous in appearance. These filaments made frequent contact with the adjacent curd matrix and with milk-fat globules.Str. cremorisNCDO 1986 produced similar surface material when in curd, but not when grown in skim-milk. In all situations, the extracellular material stained with colloidal iron hydroxide, ruthenium red and periodic acid–thiosemicarbazide–silver proteinate, indicating that it was largely composed of an acidic carbohydrate. It is suggested that this carbohydrate facilitates the adhesion of starter bacteria to the cheese-curd matrix and that during the initial stages of syneresis this serves to prevent their expulsion from the curd with the whey.