Intraepithelial bacteria were isolated by the gentamicin protection assay (GPA) from biopsy samples obtained at colonoscopy (colon cancer, n = 10 patients; colonic adenoma, n = 20; control group, n = 20; cancer patients without gastrointestinal tract GIT malignancy, n = 10). After a three-month administration of E. faecium M-74 to patients with positive GPA biopsies, 172 biopsy specimens from 60 patients were examined with the GPA. The number of biopsies with intracellular bacteria was significantly higher in adenoma and carcinoma group than in control group (26 vs. 10%; p = 0.004); in cancer patients without GIT malignancy the difference was nonsignificant. E. faecium M-74 was also administered to 5 patients with colonic adenoma; according to a control colonoscopy the number of biopsies with intracellular bacteria was significantly lower after probiotic administration (48 vs. 16%; p = 0.03). A striking prevalence of intraepithelial bacteria was also showed in patients with large bowel adenoma and carcinoma. The administration of probiotic strain M-74 can thus be considered to be an effective and promising method for elimination of pathogenic bacteria in the case of inflammatory bowel disease and colon cancer.

The development of colorectal cancer is affected by many factors, especially the intestinal microbiota. However, precise knowledge of bacterial communities associated with the mucosa in various parts of the colon is limited. Herein, we applied the gentamicin protection assay and detected the presence of intracellular bacteria in colorectal biopsies from Slovak patients with colorectal adenoma and carcinoma, and we compared this with healthy controls. The ENTEROtest 24 and MALDI-TOF mass spectrometry identified the cultivated bacteria and results revealed the presence of intracellularly localized Escherichia coli, Proteus mirabilis and Proteus vulgaris in patients with colorectal adenomas and carcinomas. In addition to these species, Klebsiella pneumoniae, Pseudomonas aeruginosa, Enterococcus faecalis and Bacillus cereus were identified in colorectal biopsies, but these were extracellular. The marked increase in relative abundance of intracellular E. coli in patients with colorectal adenomas and carcinomas was statistically significant compared to controls, and our preliminary data supports E. coli's role as a pro-oncogenic pathogen.