Fundamental study of a newly developed medium on detection of Lactobacillus.

Objective: To investigate the specificity of a newly developed Lactobacillus medium (LB medium) and its usefulness for the detection of Lactobacillus.

Method: Chlorophenol red was added to Rogosa SL Broth to make the LB medium whose pH was adjusted to 5.90. After incubation of Lactobacillus in LB medium for 24 hours, the correlation between the number of bacteria and the medium pH was examined. The change of pH was also examined when other microbes coexisted with Lactobacillus.

Results: Six species of Lactobacillus were tested. The medium pH decreased to 4 approximately 5 after incubation of any of these species for 24 hours. Though there were some differences in the acid-producing ability among species, a significant negative correlation (r = -0.93 approximately -0.99) was found between the initial number of bacteria and the medium pH with all species tested. The color of the medium did not change after incubation of other bacteria that might also be found in the normal vagina. The performance of the medium was not affected by the presence of large numbers of other microbes. In L. gasseri JCM 1131, the test microbe for color sample, the number of microbes whose color changed (red-->orange-->yellow) were approximately consistent with that of microbes reported in bacterial vaginosis (BV).

Conclusion: This method can be easily applied to detect Lactobacillus species as the number of Lactobacillus can be estimated based on the change in color of the medium for less than 24 hours after incubation.