Abstract:

Objective: To find out which ones of four polyphosphates are antimicrobial molecules and to determine their critical antimicrobial concentrations. Methods: Liquid agars at different pH values (6.0, 7.2 and 8.0) were used to test the inhibitory effects of orthophosphate, tripolyphosphate, pyrophosphate and trimetaphosphate on Bacillus subtilis and Micrococcus luteus. Results: Two of the four polyphosphates were an antimicrobial, including tripolyphosphate and pyrophosphate. Their critical concentrations causing antimicrobial positivity were 0.2 g/100mL and 0.3 g/100 mL (1157.56 mg/kg and 1601.43 mg/kg, calculated as P2O5), respectively. A two-factor, three-level orthogonal array design was employed to evaluate the synergistic antimicrobial effect of tripolyphosphate and pyrophosphate, and the results revealed that as long as one of the two polyphosphates simultaneously added had a concentration in their mixed solution equalling or exceeding its own critical concentration, a positive antimicrobial result (inhibition zone equalling or exceeding 2 mm) could be observed. Conclusion: The risk of antimicrobial positivity caused by polyphosphates can be reduced by controlling the amounts of added tripolyphosphate and pyrophosphate.

Key words: polyphosphate, tripolyphosphate, pyrophosphate, antimicrobial, microbiologic method