PITTSBURGH (AP) - The Justice Department says it has ended an investigation of inmate abuse at Pittsburgh's state prison.

The DOJ says in a Wednesday release that the Pennsylvania Department of Corrections has significantly improved security policies and practices at the prison and throughout the state prison system.

The investigation began in December 2011 after seven of the prison's officers were criminally charged for allegedly assaulting and sexually abusing vulnerable prisoners. The DOJ says the reforms to the prison are intended to protect prisoners, especially gay, transgender and gender nonconforming prisoners, from harm and discrimination.

The Pittsburgh prison has about 550 employees and houses 1,850 adult male inmates.