APPLICATION OF PERIODIC ACID-SCHIFF TYPE STAINS TO BACTERIA IN MILK

Abstract

The periodic acid-Schiff staining procedure was successfully applied to the staining of bacteria in milk. Azure A and toluidine blue O were found to be markedly superior to other dyes in the Schiff-type reagents used to stain milk smears. A more convenient variation of the usual Schiff procedure was developed in which the smear, after periodic acid oxidation, is treated successively with sulfurous acid solution and dye solution. The latter has the advantage that the reagents are stable indefinitely. Both procedures effectively stain bacteria in milk while leaving the background almost colorless. Direct microscopic clump counts of smears stained by the new methods and by North''s aniline oil methylene blue stain were compared and generally agreed well. One experiment showed better recovery of psychrophilic rods in heated whole milk. Smears stained by these new methods are considered to be easier to count because they provide much better contrast between bacteria and background than is found in smears stained with standard milk stains. Other uses of the new stains are being investigated.