Application of periodic acid-Schiff type stains to bacteria in milk.

The use of periodic acid oxidation followed by treatment with Schiff's reagent as a method for staining polysaccharides was first reported briefly by McManus (1946) and later in some detail by Hotchkiss (1948). Hotchkiss did not find the procedure particularly satisfactory for bacteria, but considered that it worked very well with many other polysaccharide materials. Despite the poor results reported with bacteria by Hotchkiss, this procedure appeared to be of possible use in staining bacteria in milk since it would stain only the bacterial polysaccharides and not the milk film itself. In some preliminary experiments using reagents prepared in a manner different from that Hotchkiss reported, the periodic acid-Schiff procedure worked fairly well as a bacterial stain but also stained the milk film rather heavily, resulting in poor contrast. Ostergren (1948), DeLamater (1951), and Kasten (1958) have reported that basic fuchsin can be replaced by other dyes in Schiff's reagent. Kasten found that any dye with a free amino group was capable of forming a Schiff-type reagent. Some of these were investigated in the present study and of the ones tested toluidine blue 0 and azure A gave the best results. These two gave excellent staining of bacteria with little staining of the milk. The staining techniques described in this paper will be of particular interest to dairy bacteriologists, but should also be of general value in bacteriology and cytology.