Author: Stier Caitlin
Institution: Biology
Date: April 2006
SUPPORT BACTERIA: IT'S THE ONLY CULTURE SOME PEOPLE HAVE.
Taken from a bumper sticker plastered to the door of a microbiology lab, this sentiment expresses a seldom-heard perspective regarding these "germs" save them, along with the subtler agenda, research them.
A short walk down the aisle of any convenience store will show you the public's contrary attitude towards microbes. We are at war. Everything seems manufactured to protect us from these microscopic creatures. Two decades ago when the household antibacterial soap market first gained popularity, these substances were simply used in cleaners. Now not only do they dominate 76% of the liquid soap market, but no application of them seems inappropriate: from ballpoint pens to children's toys, we have truly become an antimicrobial nation.
Many consumers are concerned about microbes in our environment. As consumer Steve Burrow articulates, "I've become paranoid of bacteria in my environment, [and using hand sanitizers] is something I can do to combat that. [There's] a whole population of people who are transmitting illnesses." This attitude is a common one. People are acutely aware of microbes everywhere in their environment, and these sanitizers give them a sense of control.
Figure 1. A lab technician assesses the results of an antibiotic susceptibility test. Image Courtesy: CDC.
As another consumer, Keara Martin says: "I just feel better using Purell! People are sick everywhere this time of year .The world is a dirty, germy mess in the winter, and I like to avoid it."
Despite the widespread acceptance and use of these household biocides, a key question is still unresolved: how is this form of domestic combat impacting microbes biologically? With the emergence of increasingly resistant strains of bacteria capable of enduring several types of antibiotics, many scientists believe the evolutionary repercussions of antimicrobial cleansers should be properly investigated. Could these cleansers be promoting the survival of new resistant strains? The means through which these substances work and whether they cause more harm than good is a complicated and controversial topic with which scientists continue to grapple.
The Biology of Resistance
Bacteria can develop resistance to antibiotics and biocides over many generations, quickly evolving on a microscopic level. When someone uses a hand sanitizer, for instance, it kills the majority of the microbes present, but leaves a few that have a special trait that enables them to survive. These remaining microbes, now free from competition, can grow, divide, and pass on their resistant traits to their descendents. With continued use and selection, these strains can theoretically become robustly resistant to the biocide in question. They can also spread this resistance to unrelated microorganisms by exchanging genes via transposons, so-called jumping genes that spread resistance to others without direct heredity.
Many factors can make a strain become resistant to a biocide in addition to antibiotics. First the tactic used by the antibacterial sanitizers dictates the ability of resistant strains to survive. For example, alcohol kills bacteria in such a general fashion that is difficult for microbes to adapt against it to establish resistance. Such wide scale adaptations are unlikely because they would produce a weaker or simply impossible form of the microorganism.
Unfortunately, scientists still do not know exactly how biocides target these microbes. Antibiotics unlike biocides, target precise traits unique to microbes, which make them good at killing foreign organisms without destructing your own cells, something the more general biocides are incapable of doing. However, the popular antimicrobial, triclosan, a substance found in many household soaps, has recently come under scrutiny because the way it kills bacteria mimics how some antibiotics work.
Although triclosan like alcohol employs some general antiseptic strategies, researchers have discovered that it also has a specific target that inhibits the synthesis of fatty acids, a compound critical for survival. Other antibiotics use this same strategy and thus strains that become resistant to triclosan via household use could also be resistant to these antibiotics. Fortunately, only one commonly used antibiotic, isoniazid, shares this similarity with triclosan, but other kinds of antibiotics could lose their power through a general coping mechanism that bacteria employ to be rid of this biocide as well as many drugs and antibiotics.
Figure 2. The biology behind what occurs when you wash your hands with antimicrobial soaps is a complex and important issue. Image Courtesy: CDC/Kelly Thomas.
Triclosan and many antibiotics are targets for a multi-drug efflux pump, a sort of "bacterial vomit" pump that removes these toxic compounds from the organism. In promoting the survival of strains with more active pumps and more of them, triclosan could be driving the evolution of multiantibiotic resistant strains.
As Stuart Levy, a medical researcher at Tufts University, explains in an interview for Annenberg/CPB: "We are creating an environment of bacteria that are resistant to these products, and then may well be resistant to antibiotics as well. If they have, for instance, these multi-drug efflux pumps or mutations in genes that are also targets for antibiotics, they may be resistant.there is an unfortunate mounting rage for antibacterial chemicals added to normal cleansings. And I think that this will create a changed microbiology and very likely, at least in the laboratory, contribute to the propagation of resistant bacteria."
Although this relationship between triclosan and antibiotic resistance has been found in the laboratory, no experiments as of yet have confirmed this within the general population. For example, Allison Aiello of the University of Michigan's School of Public Health, found no more resistant bacteria in households that used antimicrobial soap with triclosan than those that use regular soap. The triclosan is not producing resistant bacteria so far, but, according to Aiello and other researchers, it is also not keeping users healthier. Even though this study found no relationship, this research by no means resolves the issue. Experiments with longer trial periods may be necessary before resistance can be observed. Before the relationship or lack thereof between biocide resistant strains and antibiotic resistance can be dismissed, much more research is necessary.
Future Directions
At this point the possibility of creating antibiotic resistance through the household use of antimicrobial cleansers is an unconfirmed but real possibility. Until the science behind this issue is resolved, what do we as consumers do?
Some researchers believe that biocides are justifiable. By eliminating bacteria in our environment, antibacterial cleansers can keep people healthy so antibiotics are not needed as much. In moderating our use of antibiotics, these biocides could theoretically decrease the likelihood of antibiotic resistance caused by excessive prescription.
Hospitals in particular rely on biocides to maintain hygiene. These products have made it easier to maintain certain sanitation requirements for the patients.
As Kathyrn La Forest, a registered nurse at John Hopkins explains, during "RSV season (one of the most common illness in children that can make them terribly sick) parents coming to a child's bedside need to take precautions: gloves, masks and washing hands,Purell is way easier to get them to comply to. It's maybe not the best solution, but it's better than spreading RSV to everyone." LaForest also finds the product useful during her work in the pediatric ICU. Through such products she can prevent the spread of illnesses to other patients.
How these sanitizers should be used in household settings is a difficult issue. As Levy discusses, although these products are arguably unhelpful to most households, they can be valuable to those who have weak immune systems.
"There are no health claims for these products. Studies that have been done do not show that they have added benefit health-wise, to the healthy household. In cases of patients who are vulnerable to diseases, like cancer patients, AIDS patients, elderly diabetics, they play a role. Then they need to be used for minutes, not the few seconds that the normal person uses these products in the home," Levy said.
At the moment there are no guidelines for the use of biocides; consumers can either continue to use these products freely, use only certain ones, reserve them for special cases, or eliminate their use completely. Although, this decision is currently up to the individual, a change in perspective could be helpful, as Levy suggests in his interview for Annenberg Media.
"The problem is, we're increasing awareness of antibiotic misuse and antibiotic resistance, but there is an undercurrent of marketing of products that contain surface antibacterial chemicals to treat these problem microbes. And it's counteracting our trying to get awareness to the people that bacteria should be around. We shouldn't try to destroy them," Levy said.
For now, scientists and the general public will continue to debate about how and when we should sanitize. Although the degree to which we should "support bacteria" is uncertain, it is clear they surely merit further support in the field of research to ensure that our current infatuation with antimicrobials is not breeding disaster.