Abstract
The inhabitants of the vaginal ecosystem can harbor genetic determinants conferring antimicrobial resistance. However, detailed data about the distribution of resistance genes in the vaginal microbiome of pregnant women are still lacking. Therefore, we assessed the presence of macrolide (i.e., erm genes) and tetracycline (i.e., tet genes) resistance markers in the vaginal environment of Caucasian women at different gestational ages. Furthermore, the detection of resistance genes was related to the composition of the vaginal microbiota. A total of 228 vaginal samples, collected at different trimesters of pregnancy or during the puerperium, were tested for the presence of ermB, ermF, tet(W), and tet(M) by in-house end-point PCR assays. The composition of the vaginal microbiota was assessed through a microscopic evaluation (i.e., Nugent score) and by means of sequencing V3–V4 hypervariable regions of the bacterial 16 rRNA gene. Overall, the most detected resistance gene was tet(M) (76.7%), followed by ermB (55.2%). In 17% of women, mainly with a ‘normal’ vaginal microbiota, no resistance genes were found. Except for tet(W), a significant correlation between the positivity of resistance genes and a dysbiotic vaginal status (i.e., bacterial vaginosis (BV)) was noticed. Indeed, samples positive for at least one resistance determinant were characterized by a decrease in Lactobacillus spp. and an increase of BV-related genera (Prevotella, Gardnerella, Atopobium, Sneathia). A high predominance of vaginal Lactobacillus spp. (>85%) was associated with a lower risk of tet(W) gene detection, whereas the presence of Megasphaera (>1%) increased the risk of positivity for all analyzed genes. Different types of vaginal microbiota are associated with peculiar resistance profiles, being a lactobacilli-dominated ecosystem poor in or free of resistance genes. These data could open new perspectives for promoting maternal and neonatal health.
Highlights
In healthy reproductive-aged women, the vaginal microbiome is generally dominated by members of the Lactobacillus genus, able to promote the maintenance of the vaginal eubiosis, preventing the colonization and growth of adverse microorganisms [1,2,3,4].The depletion of lactobacilli, combined with the increase in different species of anaerobic bacteria, can result in the switch from a normal vaginal consortium to a polymicrobial dysbiosis known as bacterial vaginosis (BV) [5,6]
Cases of BV were mainly found during the first trimester of pregnancy (13/35; 37.1%) or during the puerperium (12/35; 34.3%) (Table S1)
In this study we assessed the distribution of selected tetracycline and macrolide resistance genes in the vaginal microbiota of pregnant women at different gestational ages
Summary
The depletion of lactobacilli, combined with the increase in different species of anaerobic bacteria, can result in the switch from a normal vaginal consortium to a polymicrobial dysbiosis known as bacterial vaginosis (BV) [5,6]. This condition is characterized by higher levels of different anaerobes, including Gardnerella vaginalis, Atopobium, Prevotella, Mobiluncus, and Veillonella spp. During pregnancy, the vaginal microbiome undergoes significant changes, with a marked decrease in overall diversity and enrichment in Lactobacillus spp. The ribosome protection type of tetracycline (i.e., tet genes) and the methylase type erythromycin resistance genes (i.e., erm genes) are the most common [15,16,17]
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