Bacteria stick, tenaciously and often with exquisite specificity, to sur faces ranging from the human tooth or lung and the intestine of a cow to a rock submerged in a fast-moving stream. They do so by means of a mass of tangled fibers of polysaccharides, or branching sugar molecules, that extend from the bacterial surface and form a feltlike" glycocalyx" surrounding an in dividual cell or a colony of cells. The adhesion mediated by the glycocalyx determines particular locations of bac teria in most natural environments; more specifically, it is a major determi nant in the initiation and progression of bacterial diseases ranging from dental caries to pneumonia. These major-and. with the benefit of hindsight, rather obvious-facts about the bacterial cell surface have become known only within the past decade. Ironically the main reason for the late discovery of the bacterial glycocalyx and its functions was the long reliance by microbiologists on an otherwise emi nently effective investigative system: the pure laboratory culture of an individual

NAKED BACTERIA (left) are from a typical pure laboratory culture of Escherichia coli; the glycocalyx· coated bacteria (right) are Pseudomollas cells from an iufected human bladder. In both preparations tbe cells were stained witb ruthenium red, which is taken up by any polysac. charide glycocalyx fibers that are present. The bacterial glycocalyx was ignored until recently because the familiar pure laboratory strains do not need it and therefore do not fabricate it.