Streptococcus bovis and CRC: What's the Connection?
The gastrointestinal tract is home to an extensive collection of bacterial species that provide crucial digestive and immunologic functions. When the ongoing balance between the different species within the gut becomes disrupted, it can serve as a nidus for infection and provide warning signs for potentially serious conditions such as colorectal cancer (CRC). One such example is in the case of patients who develop bacteremia with Streptococcus bovis (S. bovis).
S. bovis is normally found within the GI tract and is categorized as a group D streptococcus. Translocation of these bacteria from the GI tract into the bloodstream requires an entrance portal through the bowel wall. A portal can potentially occur through manipulation of the GI tract when procedures such as colonoscopies are performed, or if the GI tract becomes more permeable secondary to inflammation, as in the case of inflammatory bowel disease or cancer. Once in the bloodstream, the patient would be at increased risk of endocarditis as well as other significant infections.
S. bovis bacteremia may be an incidental and unexpected finding when doing a work-up of presentations other than endocarditis. In a retrospective study of 46 patients, Alazmi et al showed an association between S. bovis bacteremia and human immunodeficiency virus infection, chronic liver disease, and CRC.1 Other studies have reported a link between S. bovis bacteremia and other forms of GI cancers such as those of the esophagus, pancreas, and stomach.1 Therefore, when S. bovis bacteremia is identified in a patient, a more thorough investigation of potential GI conditions is warranted.
The association between S. bovis bacteremia and CRC is not a new one, and has been previously reported in several case reports and series since the 1950s, with many of the cases reported in patients with endocarditis.2 The new aspect is the reclassification of the S. bovis biotypes I and II, based on their molecular composition. S. bovis biotype I was given the new name Streptococcus gallolyticus Subspecies gallolyticus (SGG). This is relevant to CRC because some research has suggested that only certain subspecies of S. bovis, such as SGG, may be implicated in CRC. Boleij et al performed a meta-analysis of studies analyzing S. bovis bacteremia and CRC risk and showed that approximately 60% of patients with S. bovis bacteremia had concurrent CRC.2 More specifically, those patients with S. bovis biotype I (SGG) infection had the highest risk of CRC compared with biotype II.2 In addition, Corredoira-Sanchez et al performed a case control study that showed patients with SGG bacteremia had more advanced adenomas and invasive carcinomas.3
Although S. bovis bacteremia is not a CRC diagnostic, its presence should lead to a heightened suspicion of malignancy and the appropriate work-up should be initiated. Once S. bovis bacteremia is identified, a more detailed analysis to clarify its subtype may also help to provide answers to its true malignant potential.
- Alazmi W, Bustamante M, O'Loughlin C, et al. The association of Streptococcus bovis bacteremia and gastrointestinal diseases: a retrospective analysis. Dig Dis Sci. 2006;51(4):732-736.
- Boleij A, van Gelder MM, Swinkles DW, et al. Clinical importance of Streptococcus gallolyticus infection among colorectal cancer patients: systematic review and meta-analysis. Clin Infect Dis. 2011;53(9):870-878.
- Corredoira-Sanchez J, Garcia-Garrote F, Rabunal R, et al. Association between bacteremia due to Streptococcus gallolyticus subsp. gallolyticus (Streptococcus bovis I) and colorectal neoplasia: a case-control study. Clin Infect Dis. 2012;55(4):491-496.