Panera Bread is buying the cafe restaurant chain that its CEO Ron Shaich co-founded more than three and half decades ago.

Both chains are fast-casual chains known for their sandwiches, salads, soups and pastries. Au Bon Pain currently has 304 locations worldwide, including many in hospitals, universities, transportation hubs and urban office buildings.

The acquisition will enable Panera, a chain that promotes its healthy offerings, to catapult into new types of retail environments, it announced Wednesday.

“With the acquisition we are announcing today, we are bringing Au Bon Pain and Panera together again," Shaich said in a statement.

St. Louis-based Panera didn't disclose the terms of the deal. which is expected to close during the fourth quarter. Au Bon Pain officials could not immediately be reached for comment.

The Au Bon Pain news came half an hour before Shaich announced that he's stepping down step down as CEO effective Jan. 1, but will remain chairman of Panera’s board of directors.

He said he'll continue to work on strategy, communications and acquisitions for Panera, plus focus on his personal investments and initiatives for JAB, which acquired Panera in July.

Replacing Shaich as CEO is Blaine Hurst, Panera’s president who joined the company in January 2011 after a stint as president at Papa John’s.

More:Panera to print calories, added sugar info on its fountain-drink cups

More:Which quick-serve chains have the most loyal customers?

More:No, you're not at Panera: McDonald's goes "artisanal" with fancy sandwiches

"This is the right time for me to step down as CEO while still staying involved in the business as chairman," Shaich said. "I’ve now completed 36 years as a leader of our company and I’m particularly pleased to be able to say that Panera has been the best-performing restaurant stock of the last 20 years."

His denouement is very much like that of Howard Schultz, who stepped down as CEO of Starbucks in April to become executive chairman. Both men are known for their outspokenness on social issues and for spending more than 30 years building small cafe companies into global brands that have become one with their own identities.

Shaich prides himself on Panera's push into digital, 100% clean menu and loyalty program.

Shaich and Louis Kane created Au Bon Pain in 1981 and the company went public a decade later. In 1993, Au Bon Pain acquired the Saint Louis Bread, which was renamed Panera. Six years later, Au Bon Pain was sold off.

Luxembourg-based investment firm JAB, which also controls the Krispy Kreme chain and coffee brands Keurig and Caribou, acquired Panera out $7.5 billion this summer and took the company private.

Last month, Wall Street speculated that JAB wanted to buy Dunkin' Brands, which includes another mighty coffee chain Dunkin' Donuts.

As of late September, Panera had 2,050 locations in 46 states and Ontario, operating under the Panera Bread, Saint Louis Bread Co. or Paradise Bakery & Cafe names.

Follow USA TODAY reporter Zlati Meyer on Twitter: @ZlatiMeyer