Adsorption of Staphylococcal Bacteriophage by Milk Proteins

Abstract

Propagation of homologous bacteriophage in a culture of Staphylococcus aureus (1:1 ratio of phage to bacteria) in Trypticase Soy Broth (TSB) and in skim milk indicated more activity of phage in TSB. Early lysis of bacteria in skim milk followed by a pronounced rise in bacterial population suggested that staphylococcal phages were being inactivated by milk. Titration of phages from skim milk, whey, and TSB indicated about 90% adsorption of phages by acid- and heat-precipitable proteins of skim milk, whereas numbers recovered from whey were quite comparable to those recovered from TSB. Reducing the p H from 6.5 to 4.0 increased the percentage of phages recoverable from skim milk from 10 to 56%. Apparently, the changes in electrical charges on the casein micelles at this low p H were responsible for release of many phages from their complex with casein.