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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 pH 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 pH were responsible for release of many phages from their complex with casein.
Insights
Staphylococcal phages are inactivated by skim milk proteins, but lowering pH releases them. This study investigates phage-bacteria interactions in milk and broth, finding milk proteins impede phage activity.
Area of Science:
- Microbiology
- Food Science
- Biotechnology
Background:
- Bacteriophages are viruses that infect bacteria.
- Staphylococcus aureus is a common bacterium that can cause infections.
- Bacteriophages are being explored as therapeutic agents against bacterial infections.
Purpose of the Study:
- To investigate the propagation of bacteriophage in Staphylococcus aureus cultures.
- To determine the effect of skim milk on bacteriophage activity and survival.
- To understand the mechanism of bacteriophage inactivation in milk.
Main Methods:
- Propagation of homologous bacteriophage in Staphylococcus aureus cultures in Trypticase Soy Broth (TSB) and skim milk.
- Titration of phages recovered from skim milk, whey, and TSB.
- Experimentation with pH adjustments (from 6.5 to 4.0) to assess phage recovery from skim milk.
Main Results:
- Phage activity was higher in TSB compared to skim milk.
- Early bacterial lysis in skim milk was followed by a bacterial population rebound, suggesting phage inactivation.
- Approximately 90% of phages were adsorbed by acid- and heat-precipitable milk proteins.
- Lowering skim milk pH to 4.0 increased phage recovery from 10% to 56%.
Conclusions:
- Skim milk proteins, particularly casein, inactivate staphylococcal phages.
- Changes in electrical charges on casein micelles at low pH facilitate phage release.
- Understanding these interactions is crucial for developing phage-based therapies in dairy or food applications.