Antibacterial Mechanism of Long-Chain Polyphosphates in Staphylococcus aureus

Abstract

The results of previous studies indicated that the antibacterial effects of long-chain polyphosphates (sodium polyphosphate glassy [SPG] and sodium ultraphosphate [UP]) to Staphylococcus aureus ISP40 8325 could be attributed to damage to the cell envelope (cell wall or cell membrane). Also, Ca2+ (0.01 M) or Mg2+ (0.01 M) reversed the bactericidal and bacteriolytic effects of polyphosphates in S. aureus. In the present study, 0.4 M sodium chloride (NaCl) protected the cells from leakage caused by SPG and 0.6 M NaCl protected the cells from leakage by UP. Polymyxin, a peptide antibiotic that causes cell membrane damage, induced leakage even in the presence of 0.6 M NaCl. In the presence of 0.4 M NaCl, bacterial leakage was significantly reduced by disodium ethylenediamine tetraacetate (EDTA), a metal chelator that causes cell wall damage. Bacterial leakage by polyphosphates was significantly greater at pH 8 than at pH 6, which suggested that metal-ion chelation was involved in the antibacterial mechanism. A dialysis membrane (MWCO 100) was used to separate free metal and polyphosphate-bound metal. Levels of free Ca2+ and Mg2+ in polyphosphate-treated cells were significantly lower than those of the cells without polyphosphate. This free-metal dialysis study provided Chemical evidence to show that long-chain polyphosphates interacted with S. aureus cell walls by a metal-ion chelation mechanism. In addition, long-chain polyphosphates were shown to bind to the cell wall, chelate metals, and remain bound without releasing metal ions from the cell wall into the suspending medium. A hypothesis is proposed in which the antibacterial mechanism of long-chain polyphosphates is caused by binding of long-chain polyphosphates to the cell wall of early-exponential phase cells of S. aureus ISP40 8325. The polyphosphates chelate structurally essential metals (Ca2+ and Mg2+) of the cell wall, resulting in bactericidal and bacteriolytic effects. The structurally essential metals probably form cross bridges between the teichoic acid chains in the cell walls of gram-positive bacteria.

Inorganic polyphosphate: toward making a forgotten polymer unforgettable

“…Poly P is a safe additive to meats, enhancing water binding, emulsification, and color retention while retarding oxidative rancidity. In its use in virtually all processed meat, poultry, and fish products, poly P also serves as an antibacterial agent (31).…”

Effects of Polyphosphate Additives on Campylobacter Survival in Processed Chicken Exudates

“…However, these results are surprising given previous research that had shown that polyphosphates exhibited antimicrobial action against many food pathogens (1,8,10,12). Previous research also suggested that a possible mode of action for polyphosphate-mediated bacterial inhibition was the ability of polyphosphates to chelate divalent cations needed for bacterial cell wall formation (17). The nature of the proposed antimicrobial effect of polyphosphates would make them decidedly less effective against slow-growing or nondividing cells (18).…”

Sodium polyphosphate and polyethylenimine enhance the antimicrobial activities of plant essential oils

“…With S. aureus, 0.1% polyP caused leakage of intracellular contents and cell lysis [31]. These effects have been largely attributed to the ability of polyP to sequester structurally important divalent cations from gram-positive bacteria, a notion supported by the fact that the inhibitory effects of polyP can be avoided or reversed through the addition of divalent metal cations, such as Mg 2+ and Ca 2+ [15,[31][32][33]. It is important to note that in this work, we used CAMHB, a medium that is supplemented with both calcium and magnesium at levels of 20-25 mg/L and 10-12.5 mg/L, respectively (per manufacturer's product data sheet).…”

“…Likewise, although the OMpermeabilizing effects of polyP are well known [15,16], its potential for use as an enhancer of compounds other than antibiotics and against organisms other than gram-negative bacteria was not clear prior to our study. The physiological responses of gram-positive bacteria to challenge with polyP alone have been well characterized [31,32]. For Bacillus cereus, effects of lower levels of polyP (0.05%) included inhibition of growth, and morphological changes, including filamentation and interference with septum formation [32].…”

“…At higher concentrations, polyP caused lysis of vegetative cells and was also sporicidal [32]. With S. aureus, 0.1% polyP caused leakage of intracellular contents and cell lysis [31]. These effects have been largely attributed to the ability of polyP to sequester structurally important divalent cations from gram-positive bacteria, a notion supported by the fact that the inhibitory effects of polyP can be avoided or reversed through the addition of divalent metal cations, such as Mg 2+ and Ca 2+ [15,[31][32][33].…”