In vitro characteristics of intravaginal Lactobacilli; why is L. iners detected in abnormal vaginal microbial flora?

PURPOSE Our purpose is to investigate the reasons why Lactobacillus iners is detected in abnormal vaginal microbial flora. METHODS In this study, in vitro characteristics of four type strains (L. crispatus, L. iners, L. gasseri, and L. jensenii) were examined by measuring the growth speed by OD660, and acid resistance, with gram stain and Live/Dead stain. RESULTS The growth speed was L. gasseri > L. jensenii > L. crispatus > L. iners. Bacterial counts of all Lactobacilli in MRS medium began to decrease at the middle of the log-phase of the growth curve. In addition, L. iners grew to 106 CFU/mL and the others grew to 108 CFU/mL. L. iners was mostly Gram-negative with very short rod, while the others were mostly Gram-positive rods. L. iners was completely killed in the pH 3 medium, however, the others grew (in pH 3 medium) in 1/100 order compared with those in the pH 6 medium. CONCLUSION L. iners was not a typical gram-positive long rod Lactobacilli and presented weak acid-resistance. The reasons why L. iners is detected in abnormal vaginal microbial flora were presumed to be due to the unique morphologic and microbiologic characteristics.