From VOA Learning English, this is the Health and Lifestyle Report.

Not many people consider a bacterium that makes millions of people sick ... a friend. But scientist Roy Curtiss does.

"Yeah, I'm always looking for new uses for a bug that most people think is an enemy -- it's my friend. And I would like to make it your friend ­too."

Roy Curtiss is a microbiologist at the Biodesign Institute at Arizona State University in Tempe, Arizona. He uses the word ‘bug,' a common expression for a germ or virus, when talking about Salmonella bacteria.

Mr. Curtiss studies Salmonella and thinks it "gets a bad rap." In other words, many people only have bad thoughts when they hear the word, "Salmonella."

What is Salmonella?

Salmonella is the most common bacteria to harm, or contaminate, food. It is found in undercooked meats, eggs and milk. Salmonella can cause a higher than normal body temperature and pain in the abdomen. The person may feel sick, throwing up whatever is in the stomach.

One form of Salmonella is also responsible for the disease typhoid.

So, it is only natural that a bacterium that makes people sick is given a bad rap. The question is, "When does a food-borne bacterium become your friend?" The answer: when it helps to kill cancer cells.

"The enemy of my enemy is my friend."

Millions of people are sickened each year by Salmonella. But a genetically-engineered version of the bacteria may someday be used as a weapon against cancer. As the old saying goes, "The enemy of my enemy is my friend."

Researchers in the United States and Germany have turned Salmonella into a weapon against cancerous tumors. Roy Curtiss says the bacteria can make the cancer cells disappear.

The experiment

And here is the experiment. First, the researchers changed the genes of the Salmonella to die in healthy tissues but kill cancer cells. They put human cancer cells into mice. Then, he says, they put the genetically-modified Salmonella bacteria into the animals.

"We genetically modify the Salmonella so that it is unable to survive in healthy tissues, but has a preferential homing (attraction) to tumors, which [are] a very nutrient-rich environment where they grow like crazy and, in so doing, kill the cancer cells within the tumor."

A report describing the work was published in the medical journal mBio.

Roy Curtiss says it will be a while before the genetically-modified version of Salmonella is tested on human beings. He wants to make more changes to the bacteria to increase their cancer-killing power.

Salmonella would not be a stand-alone treatment for fighting cancer. Instead, Mr. Curtiss hopes the genetically-modified bacteria will be used in addition to more traditional therapies, such as chemotherapy and radiation.

I'm Anna Matteo.

VOA science reporter Jessica Berman wrote this report from Washington, D.C.. Anna Matteo adapted it for Learning English. George Grow was the editor.

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bad rap – idiomatic expression a negative and often undeserved reputation —often used with bum or bad (Example: He got a bad (or bum) rap by the press.)

borne – adj. carried by : spread by — used in combination as in "waterborne" and "airborne"

genetically-modified - adjective containing genetic material that has been artificially altered so as to produce a desired effect

tumor – n. a mass of tissue found in or on the body that is made up of abnormal cells

contaminate – v. to make (something) dangerous, dirty, or impure by adding something harmful

chemotherapy – n. medical the use of chemicals to treat or control a disease (such as cancer)

radiation – n. medical the use of controlled amounts of radiation for the treatment of diseases (such as cancer)