The most common virus is the common cold, which is actually caused by several different families of viruses. Even though you may experience upper-respiratory symptoms associated with a bacterial infection, most cases of the common cold are not caused by bacteria-which make antibiotics useless against them.
Colon infection is caused when harmful bacteria resides in the colon. Normally, human immune system kills the harmful bacteria but there are some strains of bacteria that grow uninterruptedly even with strong immune system. When such bacteria overgrow in the large intestine, they can cause lot of complication.
Good Flora. The good bacteria, such as Bifidobacteria and Lactobacillus, help keep these bad bacteria in check. Without the good flora, your entire colon would become over run by bad flora, which would result in symptoms like diarrhea or even illness. These protective, microscopic germs have many important functions including: