The vaginal microbiota, a reservoir of antibiotic resistance genes

Antibiotic resistance is a major challenge, in which the vaginal microbiota could play the role of a reservoir for resistance genes. This is the conclusion of a study that investigated the presence of 14 genes conferring resistance to macrolides, tetracyclines, beta-lactams, or quinolones in the vaginal microbiota of 105 Italian female students aged 19 to 30.

Resistance influenced by lifestyle

The vaginal microbiota of the students mainly belonged to CST (sidenote: Five community state types (CST) - CST I dominated by Lactobacillus crispatus, 
- CST II dominated by L. gasseri,
- CST III dominated by L. iners 
- CST V dominated by L. jensenii
- and the more diverse CST IV, which is not dominated by Lactobacillus but by a group of anaerobic bacteria, including Gardnerella, Atopobium, Prevotella, and Finegoldia. 
  ) I, dominated by L. crispatus (41.9%), and CST III, dominated by L. iners (30.5%). In terms of antibiotic resistance genes, the most frequently detected were linked to tetracyclines and macrolides: tet(M) (present in 74.3% of women), erm(F) (72.2%), erm (B) (68.6%), erm(A) (66.7%) and tet(W) (65.7%). 

The influence of lifestyle, health, and antibiotic consumption was largely confirmed, with the presence of resistance going hand in hand with:

• higher microbial diversity in the vaginal microbiota,
• smoking, which doubles the total number of resistance genes,
• a higher BMI (sidenote: Body Mass Index (BMI) Body Mass Index (BMI) assesses the corpulence of an individual by estimating the body fat mass calculated by a ratio between weight ((kg) and height squared (m2). https://www.nhlbi.nih.gov/health/educational/lose_wt/BMI/bmicalc.htm https://www.euro.who.int/en/health-topics/disease-prevention/nutrition/a-healthy-lifestyle/body-mass-index-bmi ) ,
• low use of oral contraceptives,
• poor diet quality,
• the presence of Candida spp.,
• antibiotic use in the previous year, while better past adherence to antibiotic treatment and greater awareness of resistance were associated with fewer resistance genes.

Links between bacterial taxa and antibiotic resistance

The Lactobacillus genus appeared to be protective: the more L. crispatus/jenesenii/gasseri were present, the fewer resistance genes were observed, particularly tet(M) and tet(Q). However, there were a few exceptions to this rule, with positive associations between L. gasseri and erm(A), or between L. iners and tet(Q).

Conversely, the more Gardnerella-Prevotella bacteria were present, the more macrolide and tetracycline resistance genes were observed. Similarly, several taxa associated with bacterial vaginosis (Prevotella, Dialister, Finegoldia, Porphyromonas, Anaerococcus) were linked to a higher number of resistance genes.

A reservoir of resistance

The vaginal microbiota therefore appears to represent a dynamic reservoir of antibiotic resistance genes, which are transferred to vaginal bacteria via mobile genetic elements such as plasmids (sidenote: Plasmide Petites molécules d’ADN mobiles qui peuvent passer d’une bactérie à une autre (au sein de la même espèce mais aussi entre espèces différentes). Source : https://www.pasteur.fr/fr/accueil/journal-recherche/actualites/mecanisme-defense-bacterie-escherichia-coli-fixe-resistance-antibiotique ) and transposons (sidenote: Transposons Séquence d'ADN qui présente la particularité de pouvoir se déplacer du chromosome bactérien vers un plasmide et d'un plasmide à un autre. Porteurs de gènes de résistance, les transposons jouent un rôle majeur dans la dissémination de gènes de résistances entre bactéries d'espèces éloignées. Source : https://www.vetofish.com/definition/transposon ) , making the vagina a critical site for the spread of antibiotic resistance. Since some vaginal bacteria are typical of the gut microbiota, bacterial translocation from the gastrointestinal tract to the vagina is considered a possibility.