Pork is a staple in many American diets. But Consumer Reports' lab tests of nearly 200 samples of pork chops and ground pork found cause for concern. More than two-thirds were contaminated with a bacterium called yersinia enterocolitica.

Jamie Kopf with Consumer Reports says, "This bug can cause fever and abdominal pain. And even more troubling - the vast majority of the yersinia bacteria that we found were resistant to one or more commonly used antibiotics."

Consumer Reports also found a few pork samples were contaminated with other bacteria that can also be harmful, including salmonella and staphylococcus. And, again, some of the bacteria were resistant to certain antibiotics.

Jamie adds, "Antibiotic resistance is worrisome because it can lead to infections in humans that are more difficult to treat."

On hog farms, healthy pigs are commonly given low doses of antibiotics to prevent infections and promote growth. That can accelerate the development of drug-resistant bacteria.

A second Consumer Reports test of 240 pork samples found about 20% had traces of the drug ractopamine. That's used in pigs to promote growth and make meat lean.

A major pork producer, Smithfield, says ractopamine is "a safe and effective Food and Drug Administration approved feed supplement that has been widely used in the hog farming industry for many years."

Jamie believes, "The levels we found were well below the limits set by the FDA. But Consumers Union believes that it should be banned because there isn't enough evidence it's safe for humans."

So Consumer Reports recommends buying pork raised without antibiotics and ractopamine. And it's important to cook pork thoroughly to kill any possible bacteria.

Whole pork like chops and pork tenderloin should be cooked to 145 degrees. Ground pork needs to reach 160 degrees.

As for finding pork that has not been given antibiotics or ractopamine, Consumer Reports says look for meat labeled "certified organic." Another option is to buy from Whole Foods, which requires producers not to use antibiotics or ractopamine.