The association of Streptococcus bovis/gallolyticus with colorectal tumors: The nature and the underlying mechanisms of its etiological role

One of the bacterial agents that has been found to be regularly associated with colorectal cancer is Streptococcus bovis (S. bovis). S. bovis has been shown to have important impact on health since 25 to 80% of patients with S. bovis bacteremia have colorectal tumors and the incidence of association of colonic neoplasia with S. bovis endocarditis has been shown to be 18 to 62% [1-7]. It was shown that 94% of S. bovis bacteremia associated with colorectal cancer was in fact S. bovis biotype I while only 18% was associated with biotype II [8]. Later, a new species resembling S. bovis was detected which was named S. gallolyticus [9]. Interestingly, S. bovis biotype I and II/2 isolates were then found to be S. gallolyticus [10]. Accordingly, S. bovis biotype I was renamed as S. gallolyticus subspecies gallolyticus and biotype II/2 was renamed as S. gallolyticus subspecies pasterianus and S. gallolyticus subspecies macedonicus [11] (Table 1). S. gallolyticus subspecies gallolyticus bacteria, more than other related taxa, have been found to be constantly associated with underlying colorectal cancer [10]. Therefore, the term S. bovis/gallolyticus is used in the current review.Unfortunately, the nature of the association between S. bovis/gallolyticus and colorectal cancer has long been underestimated. It has been controversial whether the association of S. bovis/gallolyticus bacteremia or endocarditis with colorectal tumors is merely a consequence of the gastrointestinal lesion or it could be of etiological nature. Furthermore, there is a growing need to highlight the possible mechanisms that S. bovis/gallolyticus might play in triggering or promoting colorectal cancer, if any. Moreover, the relationship of this bacterium with oncogenic factors, cell growth factors, and pro-inflammatory cytokines has not yet been clarified well. Therefore, the current review was done to scrutinize the nature and the underlying mechanisms of the association of S. bovis/gallolyticus with colo