2004 Volume 46 Issue 2 Pages 118-126
We identifeid the bactericidal substance, generated by Lactobacillus salivarius TI 2711 (LS 1), that kills Porphyromonas gingivalis (Pg). In an LS 1/Pg coculture system, LS 1 completely killed Pg even when added to Pg at a bacterial ratio of 1 to 1 million. Measurement of the culture supernatant of these cocultures showed an accumulation of lactic acid with 40 to 50 mmol/l at pH 6.0 or less. Incubating Pg in a culture medium containing this amount of lactic acid at a pH of 6.0 also killed a significant number of this bacterium. This suggests that the killing effect in the coculture system was exerted by either the amount of lactic acid or the pH. In the treatment of Pg with sodium hydrochloride or sodium lactate instead of lactic acid, we found that nondissociated lactic acid but not lactate anions or lower pH, is directly involved in killing Pg by LS 1 in the coculture system.
