Puppies at a national pet store chain are spreading an antibiotic-resistant infection that has so far affected 55 people in 12 states, according to the Centers for Disease Control and Prevention.

The CDC has linked a multistate outbreak of human Campylobacter to puppies sold at Petland.

The bacteria causes diarrhea, cramping, fever and abdominal pain, the health agency said on its website, and is generally treatable with antibiotics, if needed, but this case is different.

"Clinical samples from people and puppies sickened in this outbreak appear to be resistant to commonly recommended, first-line antibiotics," CDC officials said in a news release.

Not all cases of Campylobacter need antibiotic treament. Patients generally recover on their own within a week.

"If your doctor believes you need to be treated with antibiotics, they should do specialized testing to determine which antibiotic is the best choice for you," CDC public affairs specialist Brittany Behm told CNN.

People infected with the illness range in age from 1-years-old to 86. So far 13 people have been hospitalized, but luckily no one has died.

The outbreak has spread through Florida, Kansas, Maryland, Missouri, New Hampshire, New York, Ohio, Pennsylvania, Tennessee, Utah, Wisconsin, and Wyoming.

The CDC said Petland is cooperating with the investigation into the outbreak.