Introduction Streptococcus gallolyticus bacteraemia and endocarditis are associated with colorectal cancer in humans. The mechanism which drives this association is not fully understood. To investigate this, we established a model of S. gallolyticus infection in C57BL/6 mice, and investigated the effect that acute enteric colonisation with S. gallolyticus had on colonic cell turnover.
Method S. gallolyticus was isolated by blood culture from a patient who was subsequently found to have developed colorectal cancer. Groups of at least 5 young-adult male C57BL/6 mice were housed in an SPF facility, and pretreated with, or without enrofloxacin 187.5 mg/L for five days. Following a washout period, animals were administered S. gallolyticus or control broth by oral gavage daily for three days. Mice were killed seven days after the last administration of S. gallolyticus. Colonisation was confirmed by culture of colonic contents on selective media. MALDI-ToF mass spectrometry was used to validate S. gallolyticus colonisation. Sections of mouse colon were stained immunohistochemically for Ki67, cleaved-caspase 3 and γ-H2AX and subjected to quantitative histology.
Results S. gallolyticus was not identified in the faeces of any of the untreated mice, whilst all S. gallolyticus treated animals were confirmed to be colonised by culture and MALDI-ToF mass spectrometry. 57.4% (+/-2.6 SEM) of colonic epithelial cells expressed Ki67 in the antibiotic and S. gallolyticus naïve group. Significant differences were not observed following administration of either antibiotic or bacteria. In untreated animals, 7.6% (+/-2.32 SEM) of epithelial cells expressed cleaved caspase 3. Following colonisation with S. gallolyticus this increased 2.9-fold in mice that had not been treated with enrofloxacin, and 2.0-fold in mice that had been pre-treated with enrofloxacin (p<0.05 by 2-way ANOVA). To determine whether an altered DNA damage response was associated with the observed increase in epithelial cell apoptosis we quantified γ-H2AX positive cells in the colonic mucosa. In untreated mice, 41.6% (+/-5.2 SEM) of epithelial cells expressed γ-H2AX, this did not alter significantly amongst antibiotic treated, or S. gallolyticus colonised groups.
Conclusion Enteric colonisation of C57BL/6 mice with S. gallolyticus can be efficiently achieved without prior administration of antibiotics, or other manipulation of the microbiota. Acute S. gallolyticus colonisation is associated with a marked increase in colonic epithelial apoptosis. It remains to be determined whether this alteration in apoptosis has any impact on colorectal carcinogenesis, or other colonic pathology.
Disclosure of Interest None Declared
- S. bovis
- S gallolyticus
- Streptococcus bovis
- Streptococcus gallolyticus