By Bruce Horovitz, USA TODAY

It’s a PR nightmare scenario: A national fast-food chain has to respond to a video, spreading rapidly online, that shows one of its employees picking his nose and placing the result in the food he’s making. That’s exactly what Domino’s (DPZ), the nation’s largest pizza delivery chain, has spent the past several days doing.

Two employees — fired and facing charges — posted a video on YouTube on Monday that shows one of them doing gross things to a Domino’s sub sandwich he is making. Among them: sticking cheese pieces up his nose and passing gas on the salami.

The video had been viewed more than 550,000 times by Wednesday.

For Domino’s, the PR response hasn’t been easy. The video reflects some of the worst fears consumers have about food purchased from restaurants. The video and discussion of it has moved on to Facebook, Twitter and dozens of other social-networking sites.

But Domino’s is getting fairly high marks from social-networking and crisis-management gurus about its response.

And marketers are getting an instant lesson in the dangers of an online world where just about anyone with a video camera and a grudge can bring a company to its knees with lightning speed.

“Nothing is local anymore,” Domino’s spokesman Tim McIntyre says. “That’s the challenge of the Web world. Any two idiots with a video camera and a dumb idea can damage the reputation of a 50-year-old brand.”

An arrest warrant was issued Wednesday for Michael Anthony Setzer, 32, of Conover, N.C., and Kristy Lynn Hammonds, 31, of Taylorsville, N.C., for food tampering, a felony in North Carolina, police say. McIntyre says Domino’s is mulling a lawsuit.

Here are key things experts say marketers can do to quickly catch and respond effectively to similar social-networking attacks:

• Monitor social media. Big companies must actively watch Twitter, Facebook, YouTube and other social sites to track conversations that involve them. That will help uncover potential crises-in-the-making, says Brian Solis, a new-media specialist and blogger at PR2.0.

• Respond quickly. Domino’s responded within hours. “They responded as soon as they heard about it, not after the media asked, ‘What are you going to do?’ ” says Lynne Doll, president of The Rogers Group, a crisis-management specialist.

• Respond at the flashpoint. Domino’s first responded on consumer affairs blog The Consumerist, whose activist readers helped track down the store and employees who made the video. Then it responded on the Twitter site where talk was mounting. “Domino’s did the right thing by reinstituting the trust where it was lost,” Solis says.

• Educate workers. It’s important that all employees have some media and social-media training, says Ross Mayfield, co-founder of Socialtext, which advises companies on new media.

• Foster a positive culture. Workers who are content and customers who like your product are far less likely to tear down a company online, PR guru Katie Delahaye Paine says. “This would be a lot less likely to happen at places like Whole Foods.”

• Set clear guidelines. Companies must have clear policies about what is allowed during working hours — and what isn’t, Doll says. “It won’t prevent everyone from breaking the rules, but at least they’ll know what the rules are.”

As a result of the incident, Domino’s is looking at banning video cameras in stores, McIntyre says.