Scientists may now be able to explain why antibiotic-resistant bacteria is able to thrive in a hospital setting.

According to a new study, tiny circles of DNA called plasmids appear to be the culprit.  

Researchers say plasmids can easily enter bacteria and then move from one bacteria to another. 

Some plasmids even carry a gene that makes the bacteria drug-resistant.

The instance of drug-resistant bacteria has quadrupled in the last decade here in the U.S.