Ask Dr. Peg

Dear Dr. Peg,

My roommate thought she got a spider bite when she went home last weekend. It got big and sore, so she went to Student Health and they told her it was an MRSA infection. She said they cut it open and gave her antibiotics. Is this contagious? Do I need to be on antibiotics too?

Dear MRSA-mate,

I remember your roommate, or someone like her. We see a fair number of those "spider bites" here at SHAC. They start as a little red bump, which gets steadily bigger and more painful. The skin around the "bite" gets red and warm, and, eventually, the whole thing might start to drain pus. They aren't spider bites. They are boils - skin infections often caused by a kind of bacterium called Methicillin-resistant Staphylococcus aureus (MRSA, pronounced "mrrrr-suh"). This bad boy has been in the news a lot in the past few years, and for good reason. The term "resistant" in its name means that the antibiotics we used to use to treat Staph (short for Staphylococcus) infections don't kill the Staph bacterium anymore. If it doesn't get killed, it can spread to the whole body and even kill you.

To answer your question, no, you probably don't need antibiotics unless you get an infection too. You do need take basic infection precautions, like washing your hands and not sharing towels or clothing with your roommate. If you have a cut on your skin, cover it up. MRSA likes to take advantage of skin breaks as a way to get in and set up shop. That's probably how your roommate got it. If you get a sore red bump on your skin, come see us at SHAC.

And now, the rest of the story: Staphylococcus aureus means "golden cluster of seeds" in Greek, because that's what it looks like under a microscope. It is a bacterium, one we live with every day. In fact, I have read estimates that from 1 to 30 percent of Americans carry MRSA all the time without knowing it or being bothered by it. But when it decides to cause trouble, it can be serious. The Centers for Disease Control estimated that more than 94,000 people got a serious MRSA infection in 2005, and more than 18,000 died. That's more people than who died of AIDS that year.

We have been able to fight bacteria since the 1920s when penicillin was discovered accidentally by Alexander Fleming, a scientist in London. In case you don't know the story, one day he smeared a culture plate with Staph bacteria and then left it near an open window while he went on vacation for two weeks. He was working with a theory that his own snot could kill bacteria (hey, nothing else had worked so far) and probably planned to sneeze on the plate when he got back to see if it killed the Staph. The lab on the floor below his was studying molds, and a spore must have blown out their window and into his. As fate would have it, the temperature in London dropped that week to a level that was good for mold growth. The spore landed on his Staph plate and flourished there. When Fleming returned, he found his Petri dish covered with Staph bacteria - all but the area around the little mold colony where the Staph had died. Voila. Penicillin.

Unfortunately for us, bacteria are capable of adapting to their surroundings, which can include developing resistance to the drugs we throw at them. One strain of Staphylococcus, the one we now call MRSA, has done this twice since Fleming's vacation. After only about ten years, it developed resistance to penicillin, so doctors started using methicillin. This worked great for another 50 or so years, but not anymore.

If you like deep background, like I do, keep reading. I happen to think this is very cool. MRSA got its resistance from a virus. Viruses can infect bacteria, just like they can infect people. A virus that does that is called a bacteriophage, which means bacteria eater. Some phages don't actually eat the bacteria. Instead, they take up shop inside it and do things that help the bacteria survive. It's kind of like having a live-in handyman. The phages in this story merged their genes with the MRSA genes. The result was a chemical weapon produced by MRSA that neutralizes antibiotics. Now the MRSA can stay alive, which means the phage inside it can stay alive too. Mutual benefit. Tell me that isn't cool.

Taking the story one - last, I promise - step further, I can't resist telling you that phages have their uses. Some have been sprayed on crops to kill bacterial pests. One has even been approved as a food additive to kill the bacterium Listeria. Listeria causes sickness in humans and is especially dangerous in pregnant women where it can cause miscarriage, preterm delivery and even stillbirth. It likes to grow on cooked meats like hot dogs and deli meats. The FDA has approved a phage to add to these products to kill Listeria. So yes, when you are eating a ham sandwich, you might be eating a friendly virus along with it.

It is a long strange trip from boils to baloney. Isn't nature incredible? Thanks for coming along for the ride.

Peggy Spencer, M.D., is a board-certified family physician. She has been a UNM Student Health physician for 17 years and a Daily Lobo contributing columnist for three years. She is co-author of the book 50 Ways to Leave Your 40s. Drop your questions in her box in the lobby of Student Health and Counseling, or e-mail her directly at Pspencer@unm.edu. All questions will be considered, and all questioners will remain anonymous. This column has general health information only and cannot replace a visit to a health provider.