The theory behind probiotics is to use lots of beneficial microorganisms to out-compete pathogenic microbes for food sources, thereby starving the pathogens.
The objective of antibiotic use is to quickly kill the pathogenic microbes in the body to prevent further illness or death. The problem with this approach is that all the microbes are killed, leaving the body susceptible to bacterial infection. Extended use of antibiotics also leads to severe digestive problems including chronic constipation, diverticulosis, and a host of other problems. Antibiotics are helpful when there are severe cases of microbial infection. However, their use should always be followed up with the use of a probiotic to recolonize the gut.