September 16, 2026, 11:52 am | Read time: 4 minutes
Antibiotic resistance is one of the greatest challenges in modern medicine. A new study now shows that the vaginal flora might play a larger role than previously thought. Researchers found genes in more than half of the samples from pregnant women that can make bacteria resistant to certain antibiotics. Notably, differences were observed depending on the composition of the vaginal microbiome.
The Role of Vaginal Bacteria
During pregnancy, a healthy vaginal flora protects against pathogens and helps maintain the balance of microorganisms living there. At the same time, antibiotics are used to treat or prevent infections in both mother and child.
However, antibiotic-resistant bacteria are spreading worldwide. These are pathogens against which certain medications are no longer effective. The role of the vaginal flora in this development has been scarcely researched.
Researchers from France wanted to investigate more closely whether certain bacterial communities in the vagina more frequently carry so-called resistance genes. These genes can enable bacteria to protect themselves against antibiotics. Additionally, the scientists wanted to find out if there are differences between women with uncomplicated and problematic pregnancies.1
Study Design and Methods
For the study, researchers analyzed a total of 1,957 vaginal swabs from 1,547 pregnant women. The participants were cared for at three French maternity clinics. Using modern genetic analysis methods, the scientists identified which bacterial species were present in the samples and which resistance genes were detectable. They then compared different types of vaginal microbiomes. The main interest was whether certain bacterial communities contained resistance genes more frequently than others.
Additionally, the samples were associated with different pregnancy outcomes. These included uncomplicated pregnancies, preterm labor, and premature rupture of membranes–both before and at the due date.
More Than Half of the Samples Contained Resistance Genes
In 1,097 of the 1,957 samples examined, researchers found clinically relevant resistance genes. This corresponds to 56 percent of all samples. The differences between the various microbiome types were particularly pronounced. Women whose vaginal flora was predominantly characterized by the bacterium Lactobacillus crispatus had relatively few resistance genes. Three out of four samples in this group were even completely free of them.
The situation was different for women whose microbiome was dominated by Lactobacillus iners or various anaerobic bacteria. Resistance genes were significantly more common there. The most frequently detected resistance genes included lsa(C), tet(M), and erm(B). These are associated with resistance to various antibiotic groups.
Furthermore, researchers observed differences between different pregnancy outcomes. Women with a premature rupture of membranes before the expected due date more frequently had bacterial communities associated with a greater variety of resistance genes.
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Vaginal Flora as a Reservoir for Resistance Genes
The results suggest that the vaginal microbiome could be an overlooked reservoir for resistance genes. Particularly interesting is that not all bacterial communities were equally affected. Some microbiome types, especially those dominated by Lactobacillus crispatus, were associated with a significantly lower burden of resistance genes. Other communities, however, showed a much greater diversity of such genes.
According to the researchers, the composition of the vaginal flora could therefore be an important factor in better understanding the development and spread of antibiotic resistance. The results also provide new insights into how the vaginal microbiome is composed during pregnancy and what role individual bacterial species might play.
Study Context and Possible Limitations
The study is among the largest investigations to date on the relationship between the vaginal microbiome and antibiotic resistance during pregnancy. The large number of participants and the detailed genetic analyses are considered important strengths.
However, the researchers only examined resistance genes and not whether the respective bacteria were actually resistant to antibiotics. The results thus provide indications of potential resistance but do not allow conclusions about how effective antibiotics would be for individual women.
Moreover, this is an observational study. Therefore, it cannot be determined whether certain bacterial communities cause the resistance genes or if other factors are involved. The authors emphasize that further research is necessary to better understand the connections.