Lactobacillus species isolated from vaginal secretions of healthy and bacterial vaginosis-intermediate Mexican women: a prospective study

Abstract

Background: Lactobacillus jensenii, L. iners, L. crispatus and L. gasseri are the most frequently occurring lactobacilli in the vagina. However, the native species vary widely according to the studied population. The present study was performed to genetically determine the identity of Lactobacillus strains present in the vaginal discharge of healthy and bacterial vaginosis (BV) intermediate Mexican women.

Methods: In a prospective study, 31 strains preliminarily identified as Lactobacillus species were isolated from 21 samples collected from 105 non-pregnant Mexican women. The samples were classified into groups according to the Nugent score criteria proposed for detection of BV: normal (N), intermediate (I) and bacterial vaginosis (BV). We examined the isolates using culture-based methods as well as molecular analysis of the V1-V3 regions of the 16S rRNA gene. Enterobacterial repetitive intergenic consensus (ERIC) sequence analysis was performed to reject clones.

Results: Clinical isolates (25/31) were classified into four groups based on sequencing and analysis of the 16S rRNA gene: L. acidophilus (14/25), L. reuteri (6/25), L. casei (4/25) and L. buchneri (1/25). The remaining six isolates were presumptively identified as Enterococcus species. Within the L. acidophilus group, L. gasseri was the most frequently isolated species, followed by L. jensenii and L. crispatus. L. fermentum, L. rhamnosus and L. brevis were also isolated, and were placed in the L. reuteri, L. casei and L. buchneri groups, respectively. ERIC profile analysis showed intraspecific variability amongst the L. gasseri and L. fermentum species.

Conclusions: These findings agree with previous studies showing that L. crispatus, L. gasseri and L. jensenii are consistently present in the healthy vaginal ecosystem. Additional species or phylotypes were detected in the vaginal microbiota of the non-pregnant Mexican (Hispanic-mestizo) population, and thus, these results further our understanding of vaginal lactobacilli colonisation and richness in this particular population.

Figure 1

Dendrogram based on the 16S rRNA sequences of Lactobacillus strains identified in this study. The tree was generated using the neighbour-joining method. The branch lengths are proportional to the genetic distance, and the numbers shown at the branch points indicate the bootstrap values. The data set was subjected to 1,000 bootstrap replicates. The reference sequences were obtained from the GenBank database. Sequences from the clinical samples are indicated by an asterisk, and the sequence accession numbers are in parentheses (GenBank JX520600–JX520632).

Figure 2

Flow chart of Lactobacillus spp. isolation in the different participant groups. Classification was performed using Nugent’s score (normal (N), score 0–3, intermediate (I), score 4–6; bacterial vaginosis (BV), score ≥7) and hormonal status of the participants (menarche, M, and postmenopausal, P).