How did improving treatment of patients with antibiotics lead to a new problem?
antibiotics began to cause habitat destruction.
some food sources were contaminated by antibiotics.
some pathogens became resistant to antibiotics.
antibiotics began to interfere with the treatment of inherited diseases.

Some pathogens became resistant to the antibiotics.

Explanation:

The main problem that developed because of the use of antibiotics is development of  antibiotic resistant organism.

The frequent use of antibiotic on the pathogens caused mutation in their genetic material and they became resistant to it.

As a result of this there was no effect of using antibiotics on such pathogens. Due to this reason the  disease remained in the body for a longer period of time and it is not cured.