Selenium-Enriched B. longum Inhibits Tumor Growth in Mice

Bifidobacterium longum (B. longum) is a lactic acidproducing bacterium that grows naturally in the human gastrointestinal tract and defends the host against viral infection (Otles et al., 2003; Picard et al., 2005). As an anaerobe, B. longum can selectively germinate and proliferate in the hypoxic regions of solid tumors (Yazawa et al., 2000). Previous studies showed that B. longum had anticancer effects on many types of tumors, such as colon, breast and liver cancers (Singh et al., 1997; Hamaji et al., 2007). Selenium (Se), an essential micronutrient for the health of both humans and animals, exhibits its biological effect in many ways. Epidemiological data suggest that there is an inverse relationship between Se status and the risk of tumorigenesis (Karimi et al., 2012; Yadav et al., 2012), and recent studies indicated that Se compounds inhibited the proliferation and invasion of tumor cells in a variety of tumor models (Menter et al., 2000; Zeng et al., 2008; Sanmartin et al., 2012). Some groups used mouse models to study the role of Se in cancer cells and their results showed that Se exhibited antitumor activity in several tumor-bearing mouse models (Chen et al.,