The genes contained in plasmids can confer to the bacteria unusual metabolic capacities, the ability to make a sex pilus or - -

the ability to provide the bacteria with antibiotic resistance

Plasmids are small, double-stranded DNA molecules, usually in the shape of a circle, and naturally exist in cells of bacteria. They are separate from the cells chromosomal DNA and are present to carry out special functions.

The sex pili, for example, permits conjugation, which is an exchange of genetic material between bacteria.

Another alarming capability of some plasmid genes is to allow the bacteria to develop resistance to antibiotics. This is especially becoming a problem nowadays, wherein harmful bacteria infecting a host (i. e. human body) are becoming stronger, and less responsive to antibiotics.