Streptococcus bovis and colorectal cancer

Abstract

The most salient feature of Streptococcus bovis (SB) is its clinical association with malignancy of the colon and rectum. The relationship between SB and colorectal cancer (CRC) was already recognized in the 1950s and many case reports and retrospective studies on this association have been published since then. SB is an opportunistic pathogen that normally resides asymptomatically in the human intestinal tract. In compromised individuals, however, this bacterium can cause systemic infections most often presenting as bacterial endocarditis. Investigators reported the presence of colorectal tumours in up to 60% of the cases in which a patient was diagnosed with SB endocarditis or bacteremia. Therefore, these infections are nowadays often regarded as indication for full bowel examination in clinical practice. Importantly, recent studies have indicated that the association between S. gallolyticus subsp gallolyticus (previously called SB biotype I) with CRC seems much more pronounced than that of other known SB biotypes. Nevertheless, the question whether SB has a causal or predominantly incidental involvement with cancer of the colon remains to be answered. Furthermore, still little is known about the precise molecular mechanisms that determine this specific relationship. This chapter aims to summarize the literature on this subject and to illustrate possible mechanisms behind the association of SB with CRC.