Metal Ions Reverse the Inhibitory Effects of Selected Food-Grade Phosphates in Staphylococcus aureus

Area of Science:

• Microbiology
• Biochemistry
• Environmental Science

Background:

• Sodium ultraphosphate (UP), sodium polyphosphate glassy (SPG), and tetrasodium pyrophosphate (TSPP) exhibit bactericidal and bacteriolytic properties against Staphylococcus aureus.
• Low concentrations (0.1% UP, 0.1% SPG, 0.5% TSPP) are effective against early-exponential phase S. aureus cells.

Purpose of the Study:

• To investigate the influence of divalent cations (Ca2+ and Mg2+) on the antibacterial activity of UP, SPG, and TSPP against S. aureus.
• To determine if metal ions can reverse or mitigate the growth inhibition and bacteriolytic effects of these phosphates.

Main Methods:

• Metal-rescue experiments were conducted using Ca2+ and Mg2+ (0.01 M) to reverse the effects of UP and SPG on S. aureus.
• Cells were exposed to phosphates with or without pre-added metal ions, and metal ions were also added post-incubation.
• The effect of Fe3+ on TSPP-induced growth inhibition was also tested.

Main Results:

• Ca2+ and Mg2+ reversed the bacteriolytic effects of UP (0.1%) and SPG (0.1%) on S. aureus.
• Pre-incubation with Ca2+ or Mg2+ protected S. aureus from growth inhibition by UP and SPG.
• Metal-rescue experiments confirmed that Ca2+ or Mg2+ reversed the bactericidal effects of UP and SPG.
• No additive effect was observed between Mg2+ and Ca2+.
• TSPP-induced growth inhibition was not reversed by Ca2+ or Mg2+ but was reversed by Fe3+.

Conclusions:

• The antibacterial efficacy of phosphates like UP and SPG against S. aureus is significantly modulated by the presence of environmental divalent cations (Ca2+, Mg2+).
• Fe3+ can counteract the inhibitory effects of TSPP, indicating specific ion-phosphate interactions.
• Environmental metal ion concentrations are critical factors to consider when evaluating or utilizing phosphates for antimicrobial applications.