Can antibiotics cause secondary bacterial infections?

Complex answer: Antibiotics have a range of bacteria that they can kill; others outside that range are not so affected; some can become resistant to the antibiotic. If inappropriate ab is used, or taken wrong, e.g. Not as long as rx'd, can lead to more infection, with resistant germ. Bigger problem is overgrowth of a bacteria in gut (c. Difficile) during or after ab use-causes toxin and diarrhea; can be serious.

Secondary infection: Not all bacterial respond to the same antibiotics. By taking an antibiotic, there is a risk that a non-susceptible bacteria species can thrive and cause a secondary infection. As antibiotics become more powerful, this is an increasing risk. One example of this is the overgrowth of clostridium difficile in the intestine in response to antibiotics used to treat another bacterial infection.