You may have noticed more articles about the microbiome lately. Microbiome is the population of bacteria and viruses that live in our bodies. The reason you are seeing all this coverage is because we have a new way of studying these bugs. We used to put a piece of tissue or fluid on a petri dish and incubate it at a certain temperature and a certain time to see if it would grow. If we didn’t get the nutrients, temperature, or incubation time just right, a particular bug would not grow. Now we have the technology to map all the DNA and RNA in a piece of tissue or fluid. Then we subtract the human DNA and RNA, compare the remaining genetic material to databases of bacteria and viruses, and see what is left. This has demonstrated to us that there are many more bacteria and viruses normally in the body than we originally thought. In fact, scientists launched the human microbiome study and mapped the bacteria and viruses throughout the main organs but did not include the breast in their study.
It is quite remarkable since the nipple gets sucked on by babies and lovers and, since it is clearly exposed to viruses and bacteria, it may well have its own biome. There has now been a scattering of studies showing that indeed there are bacteria and viruses in breast tissue. The first body of work examined breast milk which, not surprisingly, showed bacteria. An interesting finding was the samples from obese women were different than those of normal weight women. There were also differences between women who breast fed versus bottle fed. Another study looked at breast tissue in women from Ireland and Canada and found that a diverse population of bacteria was detected within tissue collected from sites all around the breast in women aged 18-90, not all of whom had lactated. None of the women studied had signs of infection suggesting that breasts normally have bacteria and viruses.
Most interestingly, our collaborators at the John Wayne Cancer Institute in Santa Monica, California, compared the microbiome of breast cancer tissue to that of nearby benign breast tissue and found one bacterium, Sphingomonas, was more common in normal tissue than in the cancer tissue, which had much less bacteria. One suggestion from this early data is that bacteria could be protective rather than bad, keeping the immune system on its toes. The data is still early but very provocative.
Based on these studies we have decided to investigate the biome without surgery. We took samples from the milk ducts of women who had breast cancer as well as women who did not. While we are still in the process of analyzing the data, we encountered an interesting problem which shows, yet again, that things are not always what you expect. The analysis showed that the iodine solution that we had used to sterilize the breast seemed to be contaminated with bacteria. We were shocked because iodine is supposed to be sterile. But then we realized that this method of analyzing DNA counts both dead and living bacteria. While our current definition of sterile for surgery is only that no living bacteria that could cause infection are present, we don’t care about dead ones! The iodine met that definition, but must have had dead bugs in it. Science is so much fun!
Could bacteria in the normal breast be protective? It seems possible. If the bacteria originate in a mouth and are transferred by a lover or baby to the nipple then you would expect nuns to have less bacteria and more breast cancer than the normal population, which is in fact true! Wouldn’t it be amazing if breast cancer could be prevented with a probiotic?
At DSLRF, we are exploring how best to study the biome of the normal breast. Are all the ducts the same or are they different? Can we use ductal fluid or do we need a biopsy? We are excited to see what new technology brings us and what we can learn by using it.