Antibacterial Effect of Polyphosphates on Porphyromonas gingivalis

ABSTRACT

Porphyromonas gingivalis is strongly implicated in the pathogenesis of adult periodontitis, the major cause of tooth loss in adults. Use of an antibacterial agent controlling P. gingivalis as a periodontal therapeutic agent has been rationalized. The present study was performed to observe the antibacterial effect of inorganic polyphosphates (polyP) on P. gingivalis. P. gingivalis 2561 was grown in half-strength brain-heart infusion broth containing hemin and vitamin K with or without polyP. Minimal inhibitory concentration (MIC) of polyP with various chain lengths was determined by measuring the absorbance of the grown cells at 540 nm. MIC of polyP for the bacterium was determined to be 0.05%. The effect of polyP with a chain length of 75 (polyP 75) was further examined. PolyP 75 added to the growing culture of P. gingivalis at its exponential phase was as effective in inhibiting the growth of P. gingivalis as polyP 75 added at the very beginning of the culture. More than 99% of the cells lost their viability determined by viable cell count when polyP 75 was added to the culture of growing P. gingivalis at the concentration of 0.06%, suggesting that polyP 75 has a bactericidal effect on the bacterium. Intracellular nucleotide release from the cells was increased by approx. 20% in the presence of polyP 75 but was not reversed by the addition of divalent cations like Ca++ and Mg++. Under the transmission electron microscope, only a small number of the growing P. gingivalis cells were actually lysed. However, the majority of the cells appeared to be atypical in their shape, demonstrating accumulation of highly electron-dense granules and bodies of condensed nucleic acid-like material in the cytoplasm. In the presence of polyP 75, the protein profile of P. gingivalis was changed as determined by SDS-polyacrylamide gel electrophoresis and immunoblot, and the proteolytic activity of the bacterium demostrated on the zymograms was decreased. The overall results suggest that polyP have a strong bactericidal activity against P. gingivalis in which lysis in relation to chelation may not play the major role but unknown mechanism that possibly affects the viability of the bacterium may be involved. PolyP may be used as an agent for prevention and treatment of periodontitis.