There is growing evidence that alteration in the intestinal microbiome correlate with colorectal neoplasms(12, 22, 23). However, LST, as a principal precursor lesion of CRC, was never reported about the intestinal microbiota signature. Moreover, early detection and predicting the risk of adenoma recurrence after LST resection were essential to prevent CRC. Herein, the gut microbiota structure of microbiome in LST cohort by means of 16S rRNA gene sequencing was delineated in this study. The results demonstrate that LST microbial dysbiosis was characterized by relative high abundance of the genus Bacteroides-Streptococcus and the species ETBF-P. stomatis-P. micra. Based on the microbial signature, fecal microbiobial biomarkers ETBF-P. stomatis-P. micra were defined as early detection of LST. It shows that disease-associated bacteria may form a synergistic network which result in diseases. Moreover, P. stomatis behaved high accuracy on predicting adenoma recurrence after LST resections.
ETBF has been known as a contributor to chronic colonic diseases, including oncogenic transformation, intestinal inflammation, chronic colonic dysfunctions and colorectal precancerous and cancerous lesions(24-28). Combined action of the ETBF and IL-17 on colonic epithelial cells promoted the differentiation of monocytic-myeloid-derived suppressor cells(MO-MDSCs) and suppressed T-cell proliferation(27). Bacteroides fragilis-associated lncRNA1 (BFAL1) is a mediator of ETBF-induced carcinogenesis and may be a potential therapeutic target for ETBF-induced CRC(28). The recent observation of ETBF-bearing biofilms in colon biopsies from humans with colon cancer susceptibility loci strongly suggests that ETBF plays one key role in colorectal cancer(29). P. stomatis and P.micra are gram-positive anaerobic bacterium and part of the oral and gut commensal flora(30, 31). The organisms have been implicated as a causative agent of several diseases(12, 13, 30, 32-34), including oral squamous cell carcinoma(32) and apical abscess(33). A meta-analysis of 526 fecal shotgun metagenome datasets identified a microbial core of seven enriched bacteria in CRC(22). This core set included: ETBF; four oral bacteria of Fusobacterium nucleatum(35, 36), P.micra, Prevotella intermedia(37) and Porphyromonas asaccharolytica(38); and two other bacteria, Thermanaerovibrio acidaminovorans(22) and Alistipes finegoldii(39). Yachida et al(23) collected stool samples from 616 participants and found these bacteria were apparent in cases of multiple colorectal adenomas and intramucosal carcinomas. Stage-specific analyses showed two patterns of significant species elevation: the first increased across early to later stages, whereas the second was elevated only in the early stages. The former was characterized by F. nucleatum, Solobacterium moorei(37), P.stomatis, Peptostreptococcus anaerobius(40, 41), Lactobacillus sanfranciscensis, P.micra and Gemella morbillorum(42). ETBF, P.stomatis and P.micra were crucial to colorectal carcinogenesis while they were rarely reported to be biomarkers to detect precancerous lesions.
Several studies have utilized the abundance of multiple bacterial species to distinguish patients with CRC from healthy individuals. Among several bacterial candidates, F. nucleatum emerged as a key marker either when being quantified alone(16, 21) or combined with other bacteria(13, 17, 43), specifically Clostridium symbiosum(17). These findings provide support for an accurate stool-based diagnostic test using markers targeting a limited number of microbial species. In this study, the fecal abundance of the three bacteria ETBF-P. stomatis-P. micra displayed considerably high sensitivity and specialty in detecting LST, especially P. stomatis. While combinations of P.stomatis-P.micra-ETBF revealed higher diagnostic potential compared with the single biomarker P.stomatis and combined biomarkers of P.stomatis-P.micra, P.stomatis-ETBF, P.micra-ETBF. The wide application of the above bacterial markers in LST detection could be rather feasible since qPCR detection of fecal bacterial DNA in stool is technically more reliable and cost-effective than endoscopic screening.
Adenoma recurrence after endoscopic resection of LSTs is frequent(7, 8, 44, 45). Despite the widespread use of endoscopic resection, few examined the risk factors for recurrence. LSTs with cancerous histology were reported associated with the adenoma recurrence after endoscopic therapy(46). Some studies showed that independent risk factors recurrent adenoma were piecemeal resection, adjunctive argon plasma coagulation, lesion occupying 75% of the luminal circumference, lesion size >60 mm, and high grade dysplasia of LSTs(8, 46, 47). Furthermore, adenoma recurrence surveillance requests regular endoscopy screening. Many patients not developing adenoma recurrence have to subjected to frequently and ultimately unnecessary surveillance procedures. Carefully installed devices, well-trained technician and inconvenient bowel preparation before endoscopy are resource-consuming and may limit the use for population-wide screening. Based on this study, it is worth noting that the relative high abundance of P.stomatis positively correlated with adenoma recurrence after LST resection. Application of the biomarker P.stomatis to predict adenoma recurrence was therefore promising and feasible.
Furthermore, ETBF-P. stomatis-P. micra modulation, especially P. stomatis may be important for LST development, adenoma recurrence after LST resection and even colorectal carcinogenesis. Efforts need to find the best interventional approaches to manipulate the microbiota. It will necessitate concerted efforts from researchers and industrial partners to translate it into a clinical product.
However, there is no clear answer about the role of ETBF-P. stomatis-P. micra in LST or in CRC. The process is intricate and influenced by genetic and environmental factors. Mechanisms include immune regulation, metabolism of dietary components, genotoxin production and inflammation(48-50). There remained a question what are the driver and passenger bacteria in LST development? As described above, the three bacteria increased IL-6 secretion in LST group. It can be hypothesized that the three bacteria induce inflammatory environment to accelerate the development of LSTs. While it deserves in-depth studies about carcinogenesis as well as cancer therapy responses.
The strengths of the present study were as follows.First, we reported for the first time that the bacteria signature of LST. Second, we found fecal microbiome signature (ETBF-P. stomatis -P. micra) can effectively predict the occurence of LSTs. Moreover, ETBF, P. stomatis and P. micra were related to the S0 stage LST. Third, our study provided new evidence that P.stomatis exhibited the high accuracy on predicting the adenoma recurrence after endoscopic resection of LSTs.
Although clinical data for endoscopic resections was collected prospectively and all consecutive patients were included, this study was limited by its retrospective design, as all these results were from a single tertiary center and may not be generalizable. In future, studies in large cohorts enrolling more patients need to be carried out, which can derive the best diagnostic algorithm across populations.