Association of oncogenic bacteria with colorectal cancer in South China

Abstract

To quantify Fusobacterium spp., Enterococcus faecalis (E.faecalis), Enterotoxigenic Bacteroides fragilis (ETBF), and Enteropathogenic Escherichia coli in colorectal cancer (CRC) patients and their possible association with CRC clinicopathogical features, we collected the resected tumors and adjacent normal tissues (N) from 97 CRC patients. 48 age- and sex-matched healthy controls (HC) were also recruited. Real-time PCR was used for bacterial quantification. The median abundance ofFusobacterium spp.(p < 0.001, vs. N; p < 0.01,vs. HC), E.faecalis (p < 0.05, vs. N; p < 0.01, vs. HC) and ETBF (p < 0.001, vs. N; p < 0.05,vs. HC) in tumor tissues was significantly higher than that detected in normal tissue and HC. E.faecalis was detected in 95.88% of tumors and 93.81% of adjacent tissues. Fusobacterium spp. was detected in 72.16% of tumors and 67.01% of adjacent tissues. The combined E.faecalis and Fusobacterium spp. were detected in 70.10% of tumors and 36.08% of adjacent normal tissues. All four bacteria were detected in 33.72% and 22.09% of paired tumor and adjacent normal tissues, respectively. E.faecalis and Fusobacterium spp. are enriched in both tumor and adjacent tissue of CRC patients when compared to HC, suggesting that it is possible to be previously undetected changes in the pathohistologically normal colon tissue in the proximity of the tumor.

Keywords: colorectal cancer; enterococcus faecalis; enteropathogenic escherichia coli; enterotoxigenic bacteroidesfragilis; fusobacterium spp..

Figure 1. Quantitative real-time PCR analysis of bacteria in CRC tumor and corresponding normal mucous samples, presented as log10 copies/g mucosa of 50 ng DNA

The median abundance of Fusobacterium spp. (N = 97, p < 0.001, Wilcoxon signed rank test), E.faecalis (N = 97, p < 0.05, Wilcoxon signed rank test) and ETBF (N = 87, p < 0.001, Wilcoxon signed rank test) in CRC tissues was significantly higher than that in adjacent normal mucous tissues (10 cm beyond cancer margins), while there was no significance in E.coli (N = 96, p > 0.05, Wilcoxon signed rank test) between CRC tissue and adjacent normal mucous tissue.

Figure 2. Quantification of bacteria in tumor tissues, adjacent normal mucous tissues of CRC patients and control tissues from age- and gender-matched healthy volunteers

Fusobacterium spp. (N_CRC = 97, N_HC = 48; p < 0.05, Kruskal-Wallis test followed by multiple comparisons) and E.faecalis (N_CRC =97, N_HC =48; p < 0.05, Kruskal-Wallis test followed by multiple comparisons) were markedly enriched in the matched adjacent normal mucous tissues compared to the healthy controls. No difference in E.coli (N_CRC = 96, N_HC = 48; p > 0.05) and Bacteroides fragilis (N_CRC =87, N_HC =48; p > 0.05) was observed between tumor tissues, corresponding adjacent normal mucous tissues and healthy controls. **p < 0.05; ns, no significance. N_CRC, the number of CRC patients; N_HC, the number of healthy controls.