Background Smoking has been identified in observational studies as a risk factor for bacterial vaginosis (BV). The anti-estrogenic effect of smoking and trace amounts of benzo[a]pyrene diol epoxide (BPDE) may predispose women to BV. BPDE increases bacteriophage induction in Lactobacillus spp. and is found in the vaginal secretions of smokers.

Methods Vaginal microbiota of smokers versus non-smokers were compared in a cross-sectional study (Phase A, n = 40). In Phase B (n = 9) participants underwent behavioural counselling for 12-weeks and were offered nicotine patches to encourage cessation. In both Phases, participants self-collected mid-vaginal swabs (daily, Phase B) and completed behavioural diaries. Vaginal bacterial composition was characterised by pyrosequencing of barcoded 16S rRNA genes (27F-mixture and 534R, V1-V3). Vaginal smears were Nugent Gram stained. Smoking status was evaluated (weekly, Phase B) using the semi-quantitative NicAlert^® saliva cotinine test and carbon monoxide (CO) exhalation.

Results Vaginal microbiota clustered into 3 community state types (CSTs); 2 dominated by Lactobacillus (L. iners, L. crispatus),and1 lacking significant numbers of Lactobacillus spp. and characterised by anaerobes (termed CST-IV). There were statistically significant trends for increasing cotinine concentration and CO with increasing Nugent score. Smokers were 7-fold more likely to be assigned CST-IV than the L. crispatus-dominated CST (OR:7.22, 95% CI: 1.44–36.22). 4 women completed Phase B. 1 of 3 women who entered the smoking cessation with high Nugent scores demonstrated a switch from CST-IV-dominated communities to a L.iners-dominated profile with a concomitant drop in Nugent scores, coinciding with lower dose nicotine patches. The other 2 women fluctuated between CST-IV and L. iners-dominated CSTs. The fourth woman had low Nugent scores with L. crispatus-dominated CSTs throughout.

Conclusion Smokers have a lower proportion of Lactobacillus spp. Smoking cessation may shift some women to a Lactobacillus-dominated state and decrease the risk of BV. Larger studies are needed to confirm these findings.