Tolerance in Staphylococcus aureaus: evidence for bacteriophage role

Area of Science:

• Microbiology
• Bacteriology
• Molecular Biology

Background:

• Staphylococcus aureus can transition from a nontolerant to a tolerant state.
• This tolerance can be conferred to nontolerant strains via cell-free filtrates from tolerant strains.
• The acquired tolerance is heritable through serial subculturing.

Purpose of the Study:

• To investigate the nature of the converting agent responsible for inducing tolerance in Staphylococcus aureus.
• To identify the molecular components within the filtrate responsible for this conversion.
• To explore the potential role of bacteriophages in Staphylococcus aureus tolerance.

Main Methods:

• Ultracentrifugation of bacterial filtrates to isolate active components.
• Enzymatic treatment (DNase I, RNase A, Proteinase K) to identify the nature of the active agent.
• Equilibrium density gradient centrifugation in cesium chloride.
• Electron microscopy for visualization of sedimented fractions.

Main Results:

• The converting activity was fully sedimented by ultracentrifugation, indicating a particulate nature.
• Proteinase K treatment abolished the activity, suggesting a protein component.
• Equilibrium centrifugation localized the activity to a density of ~1.445 g/ml.
• Electron microscopy revealed hexagonal bacteriophages at this density.

Conclusions:

• Bacteriophages are strongly implicated as the causative agent in the conversion of nontolerant Staphylococcus aureus to a tolerant phenotype.
• The conversion involves a proteinaceous component associated with bacteriophages.
• This finding provides a novel mechanism for the development of bacterial tolerance.