Abstract
BackgroundThe association between specific bacteria and colorectal cancer (CRC) has been proposed. Only a few studies have, however, investigated this relationship directly in colorectal tissue with conflicting results. So, we aimed to quantitate Streptococcus gallolyticus, Fusobacterium spp, Enterococcus faecalis and enterotoxigenic Bacteroides fragilis (ETBF) in formalin-fixed and paraffin-embedded (FFPE) colorectal tissue samples of Iranian CRC patients and healthy controls.MethodsA total of 80 FFPE colorectal tissue samples of CRC patients (n = 40) and healthy controls (n = 40) were investigated for the presence and copy number of above bacterial species using quantitative PCR. Relative quantification was determined using ΔΔCT method and expressed as relative fold difference compared to reference gene.ResultsRelative abundance and copy number of E. faecalis and ETBF were significantly higher in CRC samples compared to control group. E. faecalis was more prevalent than ETBF in tumor samples. Frequency of ETBF and E. faecalis in late stages (III/IV) of cancer was significantly higher than early stages (I/II). We did not detect a significant difference in abundance of S. gallolyticus and Fusobacterium spp between two groups.ConclusionOur study revealed the higher concentration of E. faecalis and ETBF in FFPE samples of CRC patients than controls. However, additional investigations on fecal and fresh colorectal cancer tissue samples are required to substantiate this correlation.
Highlights
The association between specific bacteria and colorectal cancer (CRC) has been proposed
A total of 80 formalin-fixed, paraffin-embedded (FFPE) colorectal tissue samples from patients diagnosed with colorectal cancer (n = 40) and healthy controls (n = 40) were collected from archives of Pathology Department of Ayatollah Mousavi hospital in Zanjan Province, Iran
In CRC patients, 62.5% of tumors were located in distal colon and 37.5% were in proximal
Summary
The association between specific bacteria and colorectal cancer (CRC) has been proposed. We aimed to quantitate Streptococcus gallolyticus, Fusobacterium spp, Enterococcus faecalis and enterotoxigenic Bacteroides fragilis (ETBF) in formalin-fixed and paraffin-embedded (FFPE) colorectal tissue samples of Iranian CRC patients and healthy controls. Numerous studies have shown the enrichment of fecal or tissue samples of CRC patients with bacterial species such as enterotoxigenic Bacteroides fragilis (ETBF), Fusobacterium nucleatum, Clostridium septicum, Enterococcus faecalis, Streptococcus gallolyticus, Enteropathogenic Escherichia coli and pks+ E. coli [1, 4,5,6]. Several bacterial-induced carcinogenic mechanisms in CRC have been proposed including Wnt signaling activation, proinflammatory signaling and genotoxicity [5, 6]. It is proposed that long-term colonization of colonic epithelial cells with ETBF may increase the risk of CRC [4, 10]
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