Leo Brideau, the president/CEO of Columbia St. Mary's Health System since 2001, has accepted a senior position at Ascension Health, the country's largest Catholic health system and the parent of Columbia St. Mary's. He will be replaced by Mark Taylor, the president/CEO of Genesys Health System, based in Grand Blanc, MI and also part of Ascension Health, on Feb. 15. Taylor, 59, will be the third new CEO of a healthcare system in the Milwaukee area in the past two years. Peggy Troy became CEO of Children's Hospital and Health System two years ago and Susan Edwards became CEO of ProHealth Care last fall. The Medical College of Wisconsin, which employs about 1,200 doctors, also has had a new president since last summer and has begun a search for a new dean.