Cancer is the current terror of medicine, which has grown in infamy as the likes of cholera and smallpox have been counteracted by sanitation and vaccination. Cancer is a complex range of diseases that requires different approaches for therapy when compared to many of the infamous infectious diseases that were just as prevalent in the past. We may be getting some unexpected help in cancer treatments from bacteria, even though MRSA and countless others continue to plague humanity.

There is a plethora of bacteria inside a single person - collectively called the human microbiota - and there are more than ten bacteria for every single human cell in the body. Many of these bacteria are symbiotic organisms that can help us in our daily struggle to survive in a variety of ways. One example is the production of vitamin K by the gut microbiota in the intestines, an essential vitamin that the body cannot produce itself.

Recent papers published in Science this month detail the positive effect of the microbiota on cancer therapy. The presence of the gut microbiota was found to boost the effects of three antitumor regimens in mice, whilst its absence had a detrimental effect on the treatment. Whilst this result may seem removed from cancer treatment because lacking microbiota would cause many other problems (like a lack of vitamin K), this could influence clinical practice in the treatment of cancer.

It is currently common for cancer patients to be treated with antibiotics in response to their weakened immune systems. While antibiotics will stop harmful pathogens, they will also harm the microbiota, potentially causing adverse effects not previously considered in cancer therapy. This was illustrated with another experiment in which treatment of tumors in mice faltered when they had frequent antibiotic treatment.

The microbiota may also have an effect on chemotherapy. The CTX chemotherapy drug was observed to cause digestive problems, by causing villi to shrink and letting certain species of bacteria into the spleen and lymph. Feeding these bacteria to mice led to an increase of T-cells from the immune system in the spleen.

The need remains for tests in humans before we can feed specific bacteria to patients or reduce their antibiotics, but the influence of gut bacteria on the immune system is now apparent.