NASHVILLE (AP) - Hospital operator Vanguard Health Systems Inc. said Thursday former Tennessee Gov. Philip N. Bredesen has joined its board of directors.

Bredesen served as governor from 2003 to 2011 and also served as Democratic co-chair of the National Governor's Association task force on health reform, according to Nashville, Tenn.-based Vanguard. Bredesen also has served as mayor of Nashville and has helped start several health care ventures, including a health care management company from his home.

Vanguard owns and operates 28 acute care and specialty hospitals in Chicago, Phoenix and Detroit, among other cities. The company's shares debuted in June on the New York Stock Exchange after Vanguard raised $450 million in an initial public offering of 25 million shares priced at $18.

The stock has fallen steadily since its debut and closed at $9.78 on Wednesday after closing at $18.05 on June 22, its first day of trading.