Evaluation of newly isolated human vaginal lactobacilli and selection of probiotic candidates

Abstract

The probiotic relevant characteristics of 45 strains of vaginal Lactobacillus isolated from healthy women were analyzed. 21 of them were classified as L. crispatus, 17 as L. jensenii, 6 as L. gasseri and one as L. plantarum. The rate of acidification varied significantly between the strains as did the ability to form biofilms. None used glycogen as a fermentable carbohydrate. Generation of H2O2 was common, being especially frequent among L. jensenii isolates (88%). No bacteriocinogenic strains were detected. Most strains harboured plasmids (between 1 and 7) of various sizes, those in excess of 50 kb being frequent. One of these plasmids was found to be promiscuous since it hybridized with extrachromosomal bands of 15 isolates. All strains were resistant to metronidazole, ciprofloxacin, gentamicin, clindamycin, trimethoprim and sulfametoxazole and susceptible to a series of β-lactams, erythromycin, tetracycline and benzalkonium chloride. Furthermore, no amplification was found with primers that matched a series of tetracycline and erythromycin resistance genes. Almost half of the strains were highly resistant to nonoxinol 9, which is commonly used as a spermicide. Based on these analysis strains of all three common species are proposed as new probiotic candidates.