Antibacterial Mechanism of Long-Chain Polyphosphates in Staphylococcus aureus

Area of Science:

• Microbiology
• Biochemistry
• Materials Science

Background:

• Previous studies suggested long-chain polyphosphates (LCPPs) damage the cell envelope of Staphylococcus aureus.
• The antibacterial effects of LCPPs were previously shown to be reversed by divalent cations like Ca²⁺ and Mg²⁺.
• The precise mechanism of LCPP interaction with bacterial cell walls remained unclear.

Purpose of the Study:

• To elucidate the antibacterial mechanism of LCPPs against Staphylococcus aureus ISP40 8325.
• To investigate the role of metal ion chelation in the antibacterial activity of LCPPs.
• To determine how LCPPs interact with the bacterial cell wall structure.

Main Methods:

• Protective effects of sodium chloride (NaCl) against LCPP-induced leakage were assessed.
• Leakage induced by polymyxin and disodium ethylenediamine tetraacetate (EDTA) was compared.
• Dialysis studies using a membrane (MWCO 100) were performed to quantify free and bound metal ions.

Main Results:

• NaCl protected S. aureus cells from leakage induced by sodium polyphosphate glassy (SPG) and sodium ultraphosphate (UP).
• LCPP-induced leakage was pH-dependent, suggesting metal-ion chelation involvement.
• Dialysis studies confirmed lower levels of free Ca²⁺ and Mg²⁺ in polyphosphate-treated cells, indicating LCPPs chelate these metals within the cell wall.

Conclusions:

• Long-chain polyphosphates bind to the S. aureus cell wall and chelate essential structural metals (Ca²⁺ and Mg²⁺).
• This metal chelation disrupts the cell wall integrity, leading to bactericidal and bacteriolytic effects.
• The findings provide chemical evidence for a metal-ion chelation mechanism underlying the antibacterial action of LCPPs.