Some bacteria can actually help you fight other bacteria. Intestinal flora (beneficial bacteria in the gut) are an important part of your immune system. If you don't ever get the beneficial bacteria, then you have a compromised immune system.
During WWI, there was an outbreak of shigellosis among the German soldiers. There was one soldier that was unaffected. A strain of E. coli was isolated from that soldier's stool sample, and it was found that it would out-compete harmful bacteria and protect against intestinal bacterial infections. It is called E. coli Nissel after the German scientist that discovered it, Alfred Nissel. They made a pill out of it, which became the first commercial probiotic, Mutaflor.
http://www.probiotics-help.com/mutaflor.html
Mutaflor is still sold today, and you can order it on Amazon (it's pretty expensive though)
https://www.amazon.com/Mutaflor-Caps-Days-Supply-Brand/dp/B00V3MY654/ref=pd_sbs_14_1/133-5722829-2998835
During WWI, there was an outbreak of shigellosis among the German soldiers. There was one soldier that was unaffected. A strain of E. coli was isolated from that soldier's stool sample, and it was found that it would out-compete harmful bacteria and protect against intestinal bacterial infections. It is called E. coli Nissel after the German scientist that discovered it, Alfred Nissel. They made a pill out of it, which became the first commercial probiotic, Mutaflor.
http://www.probiotics-help.com/mutaflor.html
Mutaflor is still sold today, and you can order it on Amazon (it's pretty expensive though)
https://www.amazon.com/Mutaflor-Caps-Days-Supply-Brand/dp/B00V3MY654/ref=pd_sbs_14_1/133-5722829-2998835