A common classroom science activity may be dangerous and potentially fatal. Is your biology up-to-date? How about your curriculum?

The Story of Staph

Magnified 20,000X, this colorized scanning electron micrograph depicts a grouping of methicillin-resistant Staphylococcus aureus (MRSA). [Photo courtesy of CDC/Jim Biddle; photographer: Janice Carr]

Staphylococcus aureus (often called “staph”) is a common strain of bacteria that can be found on about a third of the people in the United States and around the world at any one time. It’s found on the skin of at least some students in almost every classroom. It can lead to acne-like boils or cause blistery impetigo infections that are highly contagious. Staph infections are most often spread by skin-to-skin contact. A staph infection can be minor and local—resembling a pimple—or much more serious.

Normally, staphylococcus is relatively harmless. The barrier of healthy skin, competition from nonpathogenic bacteria, and our immune system keep it at bay. But when staph bacteria enter the body through a small break in the skin, a mucus membrane, or on a catheter, they can cause disease.

In the 20th century, most staph infections occurred in people with weak immune systems, such as patients in hospitals and long-term care facilities. In most cases, penicillin and its derivatives were effective treatments. But as early as the 1960s, strains of staphylococcus that were resistant not only to penicillin, but also to the newer agent methicillin and other related drugs, were reported. These strains have a drug-resistant gene (mecA) that codes for a protein that may have been acquired from a distantly related species of bacteria. Today’s methicillin-resistant staphylococcus aureus (MRSA) may be resistant to multiple antibiotics—a lethal example of natural selection at work.

Unfortunately, MRSA is no longer rare, nor is it confined to bacteriology labs. In the past few decades, it’s become all too common in hospitals and nursing homes, requiring stepped-up scrutiny of sanitary practices and infectious disease control. People who take frequent, low doses of antibiotics or fail to finish a complete antibiotic course may be at increased risk of MRSA infection, as are people who have been hospitalized or had surgery within the past year. In 1972, it was estimated that only 2% of serious staphylococcus infections were methicillin-resistant; by 2005, that figure rose to 63% when according to the Centers for Disease Control and Prevention, MRSA caused 93,000 life-threatening infections in the United States and resulted in 19,000 deaths.

Once considered a “hospital resident,” MRSA is now recognized to be a widespread community health problem. Newer strains of MRSA (community-associated MRSA, or CA-MRSA) now circulate among otherwise healthy individuals who lack the traditional risk factors for acquiring hospital-associated MRSA (HA-MRSA). Recently, this superstrain made headlines by causing potentially serious infections in schools in at least six states. At least three student deaths were reported in October 2007. Parents and teachers were justifiably concerned; dozens of schools closed as administrators searched for effective means of disinfection and control. Presently approximately 20% of patients referred to the MassGeneral Hospital for Children Pediatric Infectious Disease outpatient practice seek management of MRSA infections, according to Dr. Mark Pasternack, chief of the Pediatric Infectious Disease Unit.

Newer antibiotics exist that can be used to treat MRSA infections, but these antibiotics are expensive, sometimes hard to get, and are more likely to have problematic side effects than the traditional ones. Without early identification and treatment, MRSA infections can occasionally have fatal consequences—devastating infections moving quickly into the bloodstream (septicemia), bones, or lungs (pneumonia.) Actor Christopher Reeve died of a rapid MRSA infection.

What You Can Do

When an epidemic of a viral disease such as influenza hits a school, clear steps can be taken, including closing the school for a period longer than the incubation period of the virus. But the situation is different with bacterial infections such as MRSA. No matter what is done, it’s possible that some staphylococcus will remain or soon return. Prevention steps such as these should be taken in schools and classrooms:

• Make sure that every classroom has access to hand-washing facilities that include warm water and soap or alcohol-based cleansers. (Remember, these are flammable.)
• Teach hand washing as an important survival skill. Because the duration and the rubbing are what prevent the infection, encourage students to extend the time and increase the vigor they use during hand washing. The time it takes to sing “Happy Birthday” or the school fight song is a good measure of how long hand washing should take.
• Involve students in communication campaigns to emphasize cleanliness and the importance of good hygiene.
• Add special lessons in hygiene for students who share locker rooms, showers, or other personal facilities.
• Communicate with parents, and share the lessons you are teaching. Encourage parents to consult their physicians at the first sign of skin infection and to keep children home until such infections disappear.

Staph Science

The epidemic has important implications for science instruction and activities. For at least 40 years, many science textbooks and now websites have suggested culturing environmental bacteria (e.g., from hands and work surfaces) to show students how common they are. That kind of activity was probably never wise, but today it’s absolutely inappropriate. (Samples of unsafe activities that should never be done in schools include those described here and here.)

Whenever students create bacterial cultures in schools, it’s almost inevitable that rich colonies of staphylococcus (along with streptococcus and other pathogens) will be produced. Placed in an optimal medium for 24 hours, a single cell might produce a colony of 109 cells/ml by the next day!

For any activity that involves environmental bacteria, student aseptic technique would have to be perfect and all waste would have to be completely sterilized to avoid serious contamination. That almost never happens in middle or secondary schools. So it’s important that teachers take these steps:

• Eliminate all science activities that might encourage the growth of environmental bacteria in schools. (Also avoid mold cultures.)
• To teach bacteriology, substitute activities that demonstrate the growth of positive bacteria, such as milk souring, compost degeneration, yogurt culture, and sugar fermentation.
• In advanced classes (such as those in community colleges), use pure, nonpathogenic strains purchased from reputable sources, and use bacterial culture equipment that result in permanently sealed cultures. Take extra precautions with biohazard waste, protecting not only students, but also the maintenance staff.

While public health historians may publish retrospectives on how inappropriate hygiene or antibiotic use led to the current MRSA epidemic, one thing is clear: These superstrains are here to stay. So this isn’t a temporary fix, but a sea change in the way we look at microbiology education. We have no other recourse than to protect the health of our students and their families by permanently adjusting best practice to eliminate the potential of culturing indigenous resistant strains of bacteria now and in the future.

For more information on MRSA, visit this U.S. government website.
Thank you to Mark Pasternack, M.D., for review of this article.