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The link between health and disease, and the human microbiome is a fast-moving area of research, and an appreciation of the variation in microbiome structures amongst individuals is expanding our understanding of the pathophysiology underlying a variety of diseases. Lactobacillus spp. was first described by Döderlein 1892 and has since been appreciated as a fundamental for maintaining vaginal health. Whilst the vagina remains one of the simplest bacterial communities, yet over a century later we are still only beginning to realise the intricacies and complexities of this ecosystem. Ravel et al. were the first to classify the vaginal microbiota (VMB) according to structure, using high-throughput sequencing of 16S rRNA gene on next generation sequencing (NGS) platforms and assigned 5 different community state types (CSTs); CST I, II, III and V are dominated by Lactobacillus crispatus, L. gasseri, L. iners and L. jensenii respectively, and CST IV conversely, is a heterogeneous group typified by depletion of Lactobacillus spp. with presence of strictly anaerobic species such as Gardnerella, Megasphera, Sneathia and Prevotella.
There is evidence that women with HPV are more likely to have decreased prevalence of vaginal Lactobacillus spp. with CST III and IV most commonly associated with HPV acquisition and persistence. CST II has also been suggested to result in the fastest clearance of an acute HPV infection.
We recently published the first study to describe the VMB in women with CIN in 169 women showing that increasing severity of CIN is associated with higher VMB diversity, and decreasing abundance of Lactobacillus spp. The frequency of CST IV was 2-fold greater in women with LSIL, 3-fold greater in HSIL and 4-fold greater in women with ICC, compared to controls, with a reciprocal decrease in frequency of CST I with increasing disease severity. In addition, women with high-grade CIN had significantly greater levels of Sneathia sanguinegens, Anaerococcus tetradius and Peptostreptococcus anaerobius and lower levels of Lactobacillus jensenii compared to those with low-grade CIN. The changes in the VMB after local cervical treatment and the impact that this may have on reproduction and the risk of preterm birth has also been a focus.