Alteration of the abundance ofParvimonas micrain the gut along the adenoma-carcinoma sequence

Parvimonas micra(P. micra) is reported to be associated with colorectal cancer (CRC). However, its association with colorectal adenoma (CRA) and its role in the initiation of colorectal tumors remain unknown. The present study aimed to clarify the relationship betweenP. micraand CRA and CRC by exploring the changes ofP. micraabundance in an adenoma-carcinoma sequence in a new cohort and 4 public sequencing datasets. To investigate the alterations ofP. micraabundance in the gut along the adenoma-carcinoma sequence, quantitative PCR (qPCR) was conducted to measure the relative abundance ofP. micrain fecal samples from 277 subjects (128 patients with CRA, 66 patients with CRC and 83 healthy individuals, as controls) who underwent colonoscopy as outpatients. Then, the relative abundance ofP. micrawas analyzed in fecal samples from 596 subjects (185 healthy controls, 158 CRC, 253 CRA) in four public 16S rRNA sequencing datasets. The qPCR results demonstrated that the CRA group had an abundance ofP. micra(P=0.2) similar to that of the healthy control group, while the CRC group had a significantly increased abundance (P=8.2x10(-11)). The level ofP. micraeffectively discriminated patients with CRC from healthy controls, while it poorly discriminated patients with CRA from healthy controls; with an area under the receiver operating characteristic curve of 0.867 for patients with CRC and 0.554 for patients with CRA. The same pattern of the alteration ofP. micraabundance, which was low in healthy controls and patients with CRA but elevated in patients with CRC, was found in all four public sequencing datasets. These results suggested thatP. micrawas closely associated with, and may serve as a diagnostic marker for, CRC but not CRA. Moreover, it was indicated thatP. micramay be an opportunistic pathogen of CRC, which may promote CRC development but serve a limited role in tumorigenesis.