CBS News -- From burgers to tacos to chili, Americans love their ground beef. Over the past year, Americans purchased 4.6 billion pounds of beef to cook at home, and half of it was in ground form. That's up 8 percent from just a decade ago.

While ground beef is convenient and often inexpensive, numerous reports show it can harbor bacteria that can cause serious illnesses, especially when the meat is undercooked. Now, new research from Consumer Reports highlights just how risky it can be to eat ground beef that's not cooked properly to the standard internal temperature of 160 degrees Fahrenheit.

For the experiment, researchers bought 300 packages of ground beef -- a total of 458 pounds -- from food stores in 26 cities across the country. They bought what's referred to as \"conventional beef,\" the most common type sold in which the cows are typically fattened with grain and soy and given antibiotics to promote growth and prevent disease, as well as beef raised in more sustainable ways. This includes organic and grass-fed cattle, but minimally means that the cows were not fed antibiotics.

\"We looked for five different bacteria associated with foodborne illness and also associated with extra intestinal infections,\" Consumer Reports' executive director for food safety and sustainability Urvashi Rangan told \"CBS This Morning. \"We also looked at antibiotic resistance on those bacteria.\"

The results showed that all 458 pounds of ground beef contained fecal contamination, which can cause blood and urinary tract infections. A bacteria called C. perfringens, which causes almost 1 million cases of food poisoning annually, was found in almost 20 percent of the samples.

In addition, \"When it came to staphylococcus aureus, we actually saw 55 percent on the conventional samples, and only about 27 percent on the sustainable samples,\" Rangan said. \"About 10 percent of the staphylococcus we found did have the toxin gene associated with foodborne illness.\"

Just 1 percent of the beef sampled contained salmonella.

Overall, the beef from conventionally raised cows was more likely to contain bacteria -- and bacteria that are resistant to antibiotics -- than beef from cows raised by sustainable methods. In fact, 18 percent of conventional beef samples were contaminated with superbugs, dangerous bacteria that are resistant to three or more classes of antibiotics. In contrast, 9 percent of sustainably-produced beef tested positive for superbugs.

While it's not unexpected to find bacteria in raw meat, Rangan emphasized that the practices associated with conventionally raised cattle are putting Americans at a greater risk.

\"Any raw meat product you're going to pick up, no matter what, you should expect that it's going to have some bacteria,\" she said. \"The question here is, 'Can we make it safer? Can it be better?' We know that it causes a lot of illnesses every year, not just from eating but cross-contamination. And when we're creating these resistance pools in the environment on the farm, these things are living and spreading and growing.\"

But those who produce conventionally-raised meat defend their methods.

\"If all cattle were grass-fed, we'd have less beef, and it would be less affordable,\" Mike Apley, chair of the Antibiotic Resistance Working Group at the National Cattlemen's Beef Association, told Consumer Reports. \"Since grass doesn't grow on pasture year-round in many parts of the country,\" he says, \"feedlots evolved to make the most efficient use of land, water, fuel, labor, and feed.\"

Rangan said the findings emphasize the need use a meat thermometer to assure meat is cooked to the appropriate temperature. Rare or medium-rare burgers are risky.

\"Remember, when it's ground beef, you're taking it and grinding the bacteria from the surface of the beef into it,\" she said. \"So unlike a steak, you're really moving all that bacteria all around the beef. So it's especially important for ground beef, to cook it to 160 degrees to be absolutely safe.\"

When shopping for ground beef, look for these labels.