Method for the Recognition of Dextrans and Levans

Dextrans and levans (which are respectively polymers of glucose anhydride and of fructose anhydride units) have long been recognized as products synthesized through action upon sucrose by a variety of bacteria from plant and soil sources. The literature on the general subject begins with the studies on "viscous fermentation" by early chemists (1) at a time when no one realized microorganisms were connected with fermentative processes, and, after passing through the period in which the dextrans (2) and levans (3) were identified chemically and in which the microbial agency was established (4), extends to the modern period in which the detailed chemical (5, 6) and serological (7-9) properties of both classes of the polysaccharides have been investigated and the enzymatic syntheses of both dextran (10) and of levan (11) have been experimentally accomplished in the absence of cells. Although the literature is abundant and is from a variety of fields, little of it deals with streptococci of human source. I-llava (12) in 1902, Oerskov and Poulsen (13) in 1931, and Koch (14) in 1933, reported the production by streptococci from throats of gum which, from the substrate spedfidty involved in its formation, can be assumed to have been either levan or dextran, although the product was not differentiated chemically. More definite evidence was presented in 1941 by the report of Niven, Smiley, and Sherman (15, 16) on the production of a chemically identified levan by strains of S. salivarius and by our (17, 18) report of the production of a dextro-rotatory polysaccharide (later chemically identified as dextran) by some strains of group H (19) streptococci. The sucrose-derived products of the group H streptococci (17, 18) and of the S. salivarius (9) were shown by us to have serological properties, which introduced the possibility of applying serological methods for the study of dextran and levan formation by streptococci.