Sterile Obsession
“I like to bathe once a week, whether I need it or not!” It’s a tired old joke, but one we’ve all heard. It speaks to how we get a little bit nervous that we might not quite be clean enough. We live in a society where we pride ourselves on being clean. Consumers spend billions of dollars each year on a dizzying array of products for personal hygiene, not to speak of the hundreds of products available to keep our homes and cars sparkling clean. But it seems that in this age of scientific innovation, we may have finally gone too far. Clean is no longer good enough. We feel the need to eradicate germs, to make sure it doesn’t just look clean, but that it is clean. Ironically, it is this national passion for sterility that may be creating a race of “superbugs,” bacteria so tough that scientists worry that soon, nothing short of a blowtorch will be able to wipe them out.
The problem is the escalating use of anti-microbial agents, with which we have unwittingly created a breeding program for drug-immune bacteria. It works like this: of all the bacteria in any one place, at first there may be only a very few individuals that, because of individual variation, are somewhat resistant to an antibiotic. When the antibiotic is used, it kills off the sensitive bacteria more quickly, leaving more resistant bacteria that can then multiply. In other words, if the antibiotic isn’t strong enough to kill all the bacteria, the stronger, more resistant ones survive. Over time, with widespread use of one antibiotic killing off “weak” bacteria, bacterial strains develop that are completely immune to the antibiotic. Even worse, bacteria transfer packets of DNA containing the genes for resistance to other bacteria, in effect sharing their secrets for defeating drugs with their neighbors.
Antibiotic Abuse
The medical use of antibiotics is a major culprit. In the United States, we now go through 50 million pounds of antibiotics each year (up from 2 million pounds per year in the 1950s). Many of these prescriptions are unnecessary, as doctors give into patients demanding antibiotics for viral diseases such as colds or the flu. Even when bacterial infections are present, if the antibiotics are not taken properly, the result is often not a cure, but a worse disease. Not finishing a prescription or using doses that are too low to kill off all the invading pathogens encourages resistant populations of bacteria to flourish. There are already strains of such dangerous microbes as Mycobacterium tuberculosis (which causes tuberculosis) and Staphylococcus aureus (which causes many of the infections caught in hospitals) that have been found to be resistant to almost every antibiotic made. The fear is that soon strains of these killer microbes will arise that are resistant to absolutely every medication we can make.
But its not just doctors and their patients that are the problem. About one quarter of the antibiotics used in this country are fed to cattle to improve their growth. Although scientists aren’t sure how this works, for some reason using very low “subtherapeutic” levels of antibiotics in the cattle feed, results in larger cattle and is believed to help prevent disease. However, there is evidence that links the chronic use of antibiotics in livestock to outbreaks of infections with drug-resistant bacteria in people, and the practice is now under scrutiny to see if it should be discontinued.
Although disease researchers have fretted about the uses and abuses of antibiotic medications for years, there may now be a more insidious culprit, inside our very own homes. In what has been called the new “antimicrobial fad,” perfectly healthy consumers are purchasing just about anything that advertises eradication of microbes. The interest in wiping out bacteria has resulted in the availability of over 700 products that contain antimicrobial agents. These germ-fighting compounds are present in soaps, mouthwash, toothpaste and lotions, household cleaners, and even in baby toys, clothing, mattress pads, high chairs, cutting boards. Antimicrobial products are mixed in with plastics to prevent bacteria, mold and fungus from growing on all manner of plastic products, ranging from cosmetic cases and medical equipment to shower stalls, paints, vinyl siding and even appliances. The problem is, rather than making our environment more germ-free, these compounds may actually be making things worse. As with antibiotic drugs, the chronic, low-level use of antimicrobials in the environment is feared to encourage the growth of resistant bacteria.
Triclosan
One antimicrobial ingredient used in hundreds of products is triclosan. Triclosan is a broad spectrum antibacterial agent, which means that it kills a wide variety of both gram positive and gram negative bacteria. Triclosan is highly toxic to bacteria because it destroys an enzyme called enoyl-acyl carrier-protein reductase, or ENR for short. Triclosan binds very tightly to the active site of the enzyme ENR, effectively and irreversibly “gumming up” the enzyme machinery. Bacteria need the ENR enzyme to make certain fatty acids for vital functions, including building cell membranes. Without ENR, bacteria can’t maintain the structure of their cell membrane, and soon die. People don’t have this enzyme, and thus triclosan is not toxic to humans.
Triclosan has been used as an effective antibacterial agent in soaps since the 1960s. Scientists long believed that triclosan assaulted multiple systems simultaneously, making it impossible for bacteria to develop specific responses. With such a broad non-specific action, it was thought that bacteria could not build up resistance to triclosan, in the same way that bacteria can’t build up resistance to bleach. This set it apart from antibiotics that specifically target one enzyme (such as penicillin, which inhibits one specific step in bacterial cell wall synthesis), which medical professionals and scientific researchers know can be defeated by bacteria. In short, no one thought that triclosan-resistant microbes could ever evolve. However, now that it has been demonstrated triclosan specifically targets ENR, scientists have found laboratory E. coli bacteria that are able to manufacture a slightly different ENR gene. Bacteria with these mutations are resistant to triclosan, With this evidence, some researchers are sounding the warning bell, noting that triclosan-resistant microbes are bound to become a problem. Not everyone agrees that this will be the case, noting that despite years of triclosan use, the only evidence of resistance to the compound is confined to the laboratory.
What Doesn't Kill You Makes You Grow Stronger
The problems with excessive use of antimicrobial compounds may reach beyond just creating “superbugs.” Indeed, overcleaning may even be harmful rather than helpful for our general health. Despite numerous commercials for household cleaners that show children playing safely in a home that has been cleaned with anti-microbial products, raising children in a too-sterile environment may actually result in health problems down the line. Not all bacteria cause disease, and developing a healthy immune system requires exposure to a wide variety of microbes. Thus, growing up in a sanitized home, where contact with microbes is minimal, can lead to a weak immune system. There are already studies out that indicate kids raised in overly clean homes show higher incidences of asthma and allergies as they grow older.
What Doesn't Kill Them Makes Them Grow Stronger
This is not to suggest that household cleaning is a bad idea. But it is how we clean that may make the difference in developing strong immune systems and keeping resistant bacteria in check. The old standbys that people have used for years, such as bleach, ammonia and hydrogen peroxide and alcohol, are highly efficient at sterilizing. The difference is that after the surface has been wiped clean, these products do not linger and continue to kill microbes. On the other hand, antimicrobial agents wiped onto a surface leaves an “antimicrobial” residue will continue to kill microbes for hours or days afterwards. Unfortunately it is not only the “bad” germs that are killed. Other, perfectly harmless bacterial are destroyed, too. In the continuing presence of the antibacterial compound, eventually, the few bacteria that do persist are all resistant microbes that will be difficult to eradicate.
Some experts are thus suggesting that you leave those antibacterial products on the shelf, and instead clean with bleach, hydrogen peroxide or alcohol. Use plain soap for handwashing (it cleans germs just as well as the more expensive triclosan-containing brands) and don’t bother with clothes or other products that have antimicrobials built in. Don’t insist on antibiotics when your doctor tells you at you have the flu, and if you do receive antibiotics for a bacterial infection, finish the whole prescription. Don’t “save some” for another time or try to share with family members or friends. In this way, antimicrobial products will be most effective where they are needed most, to help people who are really sick, and in hospitals to treat immunocompromised patients and for products used in surgery. If we are careful to not be too sterile today, we can all have a much healthier tomorrow.
Antimicrobials Web Site Links
National Antimicrobial Information Network - a joint effort to gather resources on antimicrobial compounds by Oregon State University and the U.S. government’s Environmental Protection Agency
National Center for Infectious Diseases - Antimicrobial Resistance Home Page
U.S. government Food and Drug Administration - Antimicrobial Resistance Information Page
World Health Organization - Antimicrobial Resistance Information Bank
'return to HotTopics' index