Adsorption of Lactic Streptococcal Bacteriophage by Milk Proteins

Abstract

An examination was made of the effect of varying the pH of broth, whey, and skimmilk media on the titration of lactic streptococcal bacteriophage suspended therein. For skimmilk only, a shift of pH from 9.0 to 4.0 was associated with a 78% decrease in titratable phage from pH 6.5 to 4.7, followed by a sharp increase of 85% below pH 4.7. It was concluded that at pH values above 4.7, the isoelectric point of casein, the electric charge on the casein micelles was such that phage particles were adsorbed by and formed a complex with the casein. The data suggested that when homologous host bacteria were introduced into phage-containing skimmilk at pH levels above 4.7, only a proportion of the total phage would be available for adsorption on the bacteria. As the pH was reduced below 4.7, phage particles were released by the casein and could be adsorbed by susceptible bacteria. © 1970, American Dairy Science Association. All rights reserved.