While antibiotics have saved countless lives that would have been lost due to infection, they are a double-edged sword. Antibiotics are prescribed to kill a particular pathogen, for instance, one causing strep throat. Sometimes, these antibiotics are targeted to a particular pathogen, often called Gram negative or Gram positive, but more often broad-spectrum antibiotics are prescribed to hasten the healing process.
Antibiotic-associated diarrhea is often the result of antibiotic use and directly caused by altering the gut flora. When the gut flora is altered, as it is with a round of antibiotics, pathogens are allowed to grow out of control and biofilms develop that protect these pathogens.