Inhibitory effects of heat-killed lactic acid bacterium Enterococcus faecalis on the growth of Porphyromonas gingivalis

OBJECTIVES

The effects of heat-killed Enterococcus faecalis (HkEf), a lactic acid bacterium, on the growth of Porphyromonas gingivalis were evaluated in vitro by measuring the viable cell count of P. gingivalis and gingipain activity.

METHODS

HkEf solution (1.63 or 163 mg/mL) was added to 1 mL P. gingivalis culture to generate a final HkEf concentration of 0.64 or 64 mg/mL. The cultures were incubated anaerobically. The number of viable P. gingivalis cells and gingipain activity were measured after incubation for 0, 12, 24, 48, and 72 h. The number of viable P. gingivalis cells was calculated by counting the number of colonies after culture. Gingipain activity was quantified by adding a chromogenic substrate to P. gingivalis culture medium and measuring the absorbance of the reaction solution with a plate reader. Mean ± SE was calculated for viable cell counts and gingipain activity, and Wilcoxon rank sum test was used to test for significant differences.

RESULTS

The counts of viable P. gingivalis cells in the control group increased as incubation time progressed for 12, 24, 48, and 72 h; similar results were observed in the low-concentration HkEf group. In the high-concentration HkEf group, the increase in the viable cell count was significantly inhibited compared to that of the control group. Furthermore, gingipain activity in the low- and high-concentration HkEf groups was significantly inhibited over time compared to that of the control group. Although the pH of the culture solution tended to decrease in the high-concentration HkEf group, it was not considered to have affected the growth of P. gingivalis.

CONCLUSIONS

HkEf exhibits inhibitory effects on the growth of P. gingivalis and gingipain activity.