Chipotle Mexican Grill Inc.'s founder Steve Ells will step down as chief executive of the burrito chain once it finds a replacement with "demonstrated turnaround expertise," the company said on Wednesday.

The company is struggling to recover from a string of food safety lapses that have damaged its sales and reputation and led to a slide in its stock price as well.

Chipotle's shares were up 4.4 percent at $298.40 in premarket trading on Wednesday, coming off a trading halt.

Ells will stay on as executive chairman. He was Chipotle's CEO from 1993 until 2009, when he started sharing the role with Monty Moran.

Seven years later, Ells became sole CEO after the board fired Moran amid intense pressure to turn around the burrito chain after a string of food safety lapses.

It had also named new board members following pressure from activist investor Bill Ackman.

"Bringing in a new CEO is the right thing to do for all our stakeholders," Ells said in a statement.

He said the move will help him focus on bringing innovation to Chipotle's sourcing and food preparation and that Chipotle could capitalize on opportunities, including in menu innovation, delivery, catering, and domestic and international expansion.

Chipotle said it had formed a search committee comprised of directors Robin Hickenlooper and Ali Namvar, as well as Ells, to identify a new CEO.