Cyclomodulins and Hemolysis in E. coli as Potential Low-Cost Non-Invasive Biomarkers for Colorectal Cancer Screening

Abstract

The frequent occurrence of E. coli positive for cyclomodulins such as colibactin (CLB), the cytotoxic necrotizing factor (CNF), and the cytolethal distending factor (CDT) in colorectal cancer (CRC) patients published so far provides the opportunity to use them as CRC screening markers. We examined the practicability and performance of a low-cost detection approach that relied on culture followed by simplified DNA extraction and PCR in E. coli isolates recovered from 130 CRC patients and 111 controls. Our results showed a statistically significant association between CRC and the presence of colibactin genes clbB and clbN, the cnf gene, and newly, the hemolytic phenotype of E. coli isolates. We also observed a significant increase in the mean number of morphologically distinct E. coli isolates per patient in the CRC cohort compared to controls, indicating that the cyclomodulin-producing E. coli strains may represent potentially preventable harmful newcomers in CRC patients. A colibactin gene assay showed the highest detection rate (45.4%), and males would benefit from the screening more than females. However, because of the high number of false positives, practical use of this marker must be explored. In our opinion, it may serve as an auxiliary marker to increase the specificity and/or sensitivity of the well-established fecal immunochemical test (FIT) in CRC screening.

Keywords: colibactin; colorectal cancer; cytotoxic necrotizing factor; genotoxin; screening.

Figure 1

Distribution of CRC patients by age according to the Czech National Cancer Registry compared to CRC patients included in our study.

Figure 2

Distribution of CRC location in the Czech population aged 50+ in 2014–2018 according to the Czech National Cancer Registry compared to CRC patients included in our study 2015–2019. C18—malignant neoplasm of colon, C19—malignant neoplasm of rectosigmoid junction, C20—malignant neoplasm of rectum and C21—malignant neoplasm of anus and anal canal.

Figure 3

Sex distribution in CRC patients aged 50+. Bars show relative distribution among males (blue bars) and females (red bars). For the Czech population, relative percentages are based on cumulative incidence by sex in 2014–2018 according to the Czech National Cancer Registry. For this study, relative percentages are based on absolute numbers of patients included.

Figure 4

Different burdens of distinct E. coli isolates with respect to CRC status and colibactin status. X axis represents number of distinct E. coli isolates; Y axis represents number of participants; (a) burden of all E. coli isolates irrespective of their colibactin status; (b) burden of colibactin-negative, and (c) colibactin-positive isolates.