Population Characteristics
Samples were collected from November 2020 to April 17, 2021, from a total of 624 enrolled participants. According to the exclusion criteria (see Methods section), 201 participants were excluded. A total of 423 samples were finally included in this experiment (Table 1). Detailed information was available in the Supplementary material S1, Database 1, Table 1.
According to the recommendations of the American Cancer Society (ACS), women with a cervix should undergo routine cervical cancer screening at least every five years starting at age 25 years until 65 years. We selected women between the age of 25 and 65 years as our participants. There was no significant correlation between HPV infection and postmenopausal status, number of gestations and pregnancies, or use of condoms, but there were significant correlations between age, regular use of contraception, presence of an intrauterine device, and number of sexual partners. Of the 423 samples obtained, 160 out of 423 (37.8%) of the women had BV infections. The HPV-negative group had significantly lower rates of BV infection than the HPV-positive group (P < .001). A total of 230 out of the 423 samples (54.4%) had HR-HPV and 86 out of the 230 samples (37.4%) had more than one type of HPV. Women with HR-HPV who progressed to CIN were 94 out of 230 (40.9%).
Population Characteristics by HPV Status
Table 1
Population Characteristics by HPV Status (total n=423). Age was displayed as years and IQR (interquartile range), continuous variables were presented as mean ± standard deviation (SD), and others were showed as frequencies and proportions. * HR-HPV-positive group compared with HPV-negative group ** Among women of the “contraception” group
Variables
|
HPV-negative
(n=193)
|
HR-HPV–positive
(n=230)
|
P value *
|
Demographics
|
|
|
|
Age (y; [IQR])
|
35 (30~41)
|
36.5 (31~44)
|
0.041***
|
Postmenopausal (n [%])
|
13 (6.7)
|
18 (7.8)
|
0.668
|
Pregnancy, mean (±SD)
|
1.46 (±1.01)
|
1.57 (±1.02)
|
0.288
|
Gestation, mean (±SD)
|
1.03 (±0.67)
|
1.07 (±0.73)
|
0.676
|
Sex behavior characteristics
|
Contraception (n [%])
|
190 (98.4)
|
209 (90.9)
|
0.001***
|
Condom use (n [%]) **
|
159 (83.7)
|
188 (90.0)
|
0.063
|
IUD implant (n [%]) **
|
29 (15.3)
|
18 (8.6)
|
0.04***
|
Number of sexual partners, mean (±SD)
|
1.01 (±0.12)
|
1.12 (±0.35)
|
0.001***
|
Clinical status
|
|
|
|
BV infection (n [%])
|
54 (28.0)
|
106 (46.1)
|
0.001***
|
Multiple HPV infection
(n [%])
|
0 (0)
|
86 (37.4)
|
0.001***
|
CIN (n [%])
|
0 (0)
|
94 (40.9)
|
0.001***
|
*** statistically significant, P < .05 vs. the HPV-negative group
Next, we conducted logistic regression analysis on possible risk factors for CIN including age, postmenopausal period, number of gestations and pregnancies, methods of contraception, number of sexual partners, BV, senile vaginitis, HPV infection, and multitype HPV infection, which were collected in the questionnaire. We found that condom use (OR=3.480; 95% CI=1.069-11.325; P < .05) was a protective factor for CIN, whereas BV (OR=0.358; 95% CI=0.195-0.656; P < .05) and HR-HPV infection (OR=0.016; 95% CI=0.004-0.072; P < .001) were risk factors for CIN.
The Difference in Composition of Vaginal Microbiota in the HPV-negative and HPV-positive Groups
To identify the difference in composition of vaginal microbiota between women with and without HPV infection, we sequenced the V3-V4 hypervariable region of the 16S rDNA gene utilizing 16S rRNA sequencing. We acquired 15 137 OTUs in our experiment, the sequence result was available in Supplementary material S2, Database 2 and the taxonomy profile was in supplementary S2, Table 1.
In the HPV-negative group, 8 out of 193 samples and 1 out of 230 samples in the HPV-positive group were excluded because of low DNA copy numbers. The relative abundance of the top 19 prevalent vaginal microbiota in HPV-negative and HPV-positive women samples with Lactobacillus spp. predominant in both groups are displayed in Figures 2A and 2B. As shown in Figure 2C, the abundance of Lactobacillus spp. in the HPV-negative group was much higher than that in the HPV-positive group. Meanwhile, microbiota composition in the HPV-positive group was more complicated. Bacteria such as Gardnerella vaginalis, Ralstonia pickettii, Streptococcus anginosus, Prevotella bivia, Prevotella timonensis, Bifidobacterium dentium, and Sneathia sanguinegens presented more frequently in the HPV-positive group. We analyzed the OTUs numbers in each group and displayed them in a Venn graph in Figure 2D. The unique OTUs in the HPV-positive group were significantly higher than in the HPV-negative group. These data suggest that HPV infection could lead to an increase in vaginal microbiota complexity.
The Relative Abundance of Vaginal Microbiota of Different BV, HPV and CIN Statuses
To further estimate the impact of BV and HPV infection on vaginal microbiota changes during CIN progression, we divided all the samples into 6 groups according to the following BV, HPV or CIN statuses: Normal, BV (BV infection), HPV (HR-HPV infection), B.H (BV and HR-HPV co-infection), H.C (HR-HPV infection combined with CIN), and B.H.C (BV and HR-HPV co-infection combined with CIN). To better distinguish the differences between groups, we conducted random screening of the grouped data to balance the sample size of each group. A total of 342 samples were collected and the numbers of final samples of each group were 65, 52, 71, 60, 48, and 46, respectively (Supplementary material S1, Database 1, Table 2, 3, 4, 5, 6 and 7 for detailed information). In Figure 3A, we displayed the top 19 vaginal microbiota at the species level. Lactobacillus spp. had the highest percentage relative abundance of up to 82.6% in the normal group. Women with HPV infection only showed little change in the Lactobacillus spp. genera in their vaginal microbiota, but the percentage of L.crispatus, which presented most in a healthy vaginal environment was partly replaced by L.iners. Lactobacillus spp. and lost its dominance (with less than 60% in composition) in the remaining three groups of women, who were all diagnosed with BV infection with a more complex bacterial composition.
We defined the community state types (CSTs) according to the dominant (> 60% of relative abundance in one sample) Lactobacillus species type. CST I, II, III, V were dominated by L. crispatus, L. gasseri, L. iners, and L. jensenii, respectively, whereas CST IV was defined as the depletion of Lactobacillus spp. Surprisingly, the CST II cluster was only shown in the normal group and CST V in the BV group. The transformation of CST I to CST III was most apparent in the HPV-positive group, which indicated that L.iners may be a key species during HPV infection. Women diagnosed with BV infection were more likely to be defined as being in the CST IV cluster. Interestingly, the percentages of CST IV cluster among BV and HPV co-infected women with CIN were significantly lower than those in the B.H group, and CST III cluster percentage was increased, which also indicates the importance of L.iners.
Higher Microbial Diversity in Women with BV and HPV Co-infection
The observed species, Shannon diversity, and Chao1indexes were used to measure the alpha diversity of microbiomes in 6 groups. High variability was observed among the samples; thus outliers were not shown in the boxplot (Figures. 4A, 4B, and 4C). Three indexes of microbial diversity in the BV, HPV, B.H, and B.H.C groups were all significantly higher than those in the normal group, which indicated that either BV or HPV infection could disturb the balance of vaginal flora (P < .001). Besides, the observed species and the Chao1 index of the H.C group were lower than those of the BV, HPV B.H, and B.H.C groups (P < .001). The Shannon indexes for the HPV and H.C groups were significantly lower than that of the B.H.C group (P < .001). The P values above were all calculated by the Wilcoxon rank-sum test.
The beta diversity was measured with the PCoA based on the Bray–Curtis dissimilarity. All the samples were mainly separated into three groups related to CST clusters [P < .001 (Figure 4D)]. P values were calculated by the ANOSIM test. Biodiversity was not dependent on BV, HPV, or CIN status (supplementary Figure 1).
Important Phylotype in CIN Progression
To find out which bacteria are responsible for the community differences between groups, we used LEfSe to analyze the bacterial diversity and find biomarkers. It combines statistical difference analysis and the impact score of the species on the grouping results while emphasizing statistical significance and biological relevance. Figure 5A and 5B mainly show the species with significant differences in linear discriminant analysis (LDA) score greater than 3.5, which is the marker with a statistical difference. Like a previous study, we found a significant enrichment of Lactobacillus genera in the normal group compared with the group with BV or HPV-infected women. Anaerobic bacteria associated with BV infection such as the Prevotellaceae family, Streptococcaceae family, Atopobiaceae family, and Enterobacteriaceae family were significantly different among BV and HPV co-infected women compared with those in the normal group. These data suggest that CIN development could not be attributed to a single species but the result of multiple species interaction.
Gene Functional Pathways of Bacterial Taxa Associated with BV, HPV or CIN
To better understand the bacterial function during disease progression, we also explored microbiota function using PICRUSt (Phylogenetic Investigation of Communities by Reconstruction of Unobserved States). [12] Gene we detected were matched with the KEGG (Kyoto Encyclopedia of Genes and Genomes) database, predicted raw data was available in Supplementary S4, Database 3. [13,14] The KEGG pathway we tested was presented in supplementary Figure 2. There were many non-human gene pathways in different groups including pathways related to metabolism, genetic information processing, environmental information processing, cellular processes, and organismal systems. There were 33 pathways changes in the B.H.C group compared with the ones with healthy women (P < .05). Pathways related to amino acid, energy, cofactors, vitamin metabolism, biosynthesis of other secondary metabolites, folding, sorting and degradation, and endocrine systems were enriched in the B.H.C group women, whereas carbohydrate metabolism (glycolysis/gluconeogenesis, galactose, and glycerol-lipid metabolism) pathways were depleted in the B.H.C group (Fig 6). Depletion of membrane transporters and carbohydrate metabolism pathways was more frequent in the diseased versus normal groups, which may indicate that bacterial functions were mainly associated with these two pathways.