Published online by Cambridge University Press: 15 September 2009
It has been estimated that more than 80% of human cancers are caused by environmental factors, and so are potentially preventable (Higginson, 1968). Bacteria are in a unique position to mediate between the host and its external environment because they naturally colonise all external surfaces. In addition, bacterial infections expose the host to further interactions with bacteria.
The role of the flora in protecting the host against infection has been well documented. The normal bacterial flora of the mouth protects against fungal infection; the normal flora of the intestine helps to protect against enteritis; the normal skin flora helps to protect against skin infection.
Furthermore, the gut bacterial flora has an overwhelmingly beneficial role in assisting digestion and in detoxifying ingested compounds of exogenous origin (Hill, 1995). However, there are situations where bacterial infection, which can be defined as bacteria being in the wrong place, can produce carcinogens and is associated with local cancers (e.g., bladder infection, nitrosamines, and bladder cancer). In addition, there are situations where the normal flora, carrying out its normal metabolic activity, can be exposed to very high levels of a substrate resulting in toxic levels of the product (e.g., colon bacteria, bile acids, and colon cancer).
In this chapter we will first discuss the types of carcinogens/mutagens that can be produced by bacterial action, and the situations in which this production might be significant. In addition, the gut bacteria release a wide range of anti-carcinogens from the diet as well, and these are discussed.
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