Discussion
This is the first study performed to characterize the vaginal microbiome
in women with POI. The study revealed that, for women with POI using
systemic HT, and by means of analysis by DNA extraction, the vaginal
flora is predominantly
Lactobacillus sp., which is the flora considered healthy and suitable
for estrogenized women. There was a predominance of L. cripatusin the same proportion of L. iners , followed at a smaller
proportion by L. gasseri and L. jensenii . It should also
be considered that Ravel group IV bacteria were present in 15.2% of the
cases, even though these women were adequately estrogenized by systemic
HT ( 15-19).
Studies with evaluation of the vaginal flora, through different methods,
reveal that to maintain a healthy vaginal ecosystem, it is necessary to
have superior counting of Lactobacillus sp colonies in order to maintain
adequate pH through the production of acids, especially lactic acid, to
prevent pathogenic bacterial proliferation (20-22). A study in which the
authors compared the vaginal flora (but not the microbiome) of women
with POI using HT, with women of the same age with preserved gonadal
function by means of bacterioscopy and culture for fungi, showed similar
floras, with no difference between groups. Thus, it can be assumed that
systemic HT was able to provide sufficient estrogenic levels to restore
the vaginal flora, despite loss of ovarian function (23).
Considering that common
evaluation methods of the vaginal ecosystem have no specificity for
which species of lactobacilli are present and that different species of
lactobacilli produces different types of acids and concentrations, the
present study used up-to-date techniques (DNA study of the vaginal
flora). The specific phylogenetic
classification of women with POI may provide evidence of HT action on
the vaginal flora restoration (24).
Molecular biology has become a great ally in the search for vaginal
flora identification. Efforts to characterize vaginal microbial
communities using culture methods undoubtedly led to significant
improvements in understanding the role of microorganisms in vaginal
health, but they were limited because of the biases inherent in
culturing methods. It is now known that most environmental
microorganisms associated with the host are not identified in the
laboratory using traditional cultivation techniques (25).
Culture of microorganisms is fundamental for the understanding of their
physiological and phenotypic characteristics, and it continues being a
very useful tool in studies of microbial ecology. Promising developments
in the cultivation of fastidious bacteria using state-of-the-art
techniques are likely to enable the cultivation of many previously
inaccessible microorganisms (26-29). However, studies aimed at
evaluating fine-scale variation in host-associated microbial communities
within and between individuals or exploring ecological relationships
within those communities require methods that provide detailed
information on microbial diversity and, at the same time, be scalable
for processing samples and also cost-effective. In response to this
need, independent culture methods have become, in recent years, the
standard approach to characterize the diversity of microorganisms
residing in the human body (30-34).
Ravel et al. found that the group I communities in healthy women of
reproductive age, which occurred in 26.2% of the women that they have
studied, were dominated by L. crispatus, while groups II (6.3%), III
(34, 1%) and V (5.3%) were dominated by L. gasseri, L iners and
L. jensenii, respectively. Curiously, communities dominated by
Lactobacillus species other than L. crispatus have slightly
higher pH, ranging from 4.4 (group III) to 5.0 (group II), indicating
that these communities as a whole may not produce as much acid as group
I (4). These results are in agreement with the findings in the present
study, where there was also a predominance of groups I (L.
crispatus ) and III (L. iners ), indicating a healthy vaginal
flora and a percentage expected for estrogenized women. Thus, it is
possible to infer that HT in women with POI may be able to maintain
adequate vaginal flora.
Two important points will have to be clarified in the future.
Intriguingly, we found 15.2% of bacteria associated with bacterial
vaginosis in adequately estrogenized women. Second, there is no
predominance of L. crispatius on L. iners. These two points may point
out that the use of systemic estrogens is not sufficient to determine
vaginal colonization with L crispatus, producers of lactic acid.
Probably, other factors such as frequency of sexual intercourse, type of
sexual practices, feeding, individual immune response, among others, may
interfere with vaginal colonization.
Although this study is one of the first in literature to evaluate the
vaginal flora of young women, with POI undergoing systemic hormone
therapy, by using advanced and reliable technique such as the evaluation
of vaginal microbiology through molecular biology with the 16S rRNA
pyrosequencing, we understand that the fact of having been a descriptive
study only limits our conclusions or future inferences, as is already
known in the descriptive studies. The small sample size also makes us
understand that the findings are limited to this group studied and that
further studies are needed with larger cases where there is comparison
with women using topical replacement therapy and/or with women at
menacme with preserved ovarian function. On the other hand, we have to
consider that the studies with POI, do not have large case-by-case
studies due to the difficulties inherent in this nosological entity.
Work with large case-by-case studies about POI often come from databases
involving several institutions.