Science of Resistance: Antibacterial Agents
When Louis Pasteur demonstrated that bacteria are the agents that cause many infections, people were better able to understand how diseases begin and spread. Ironically, however, even though Pasteur's findings demystified infectious disease, they also led to fear of "germ" contamination. This fear was not allayed until the last half of the twentieth century when antibiotics were discovered and used clinically.
Antibiotics were considered miracle drugs when they were first introduced. Many people felt that diseases caused by bacteria were conquered and soon would no longer exist. Unfortunately, however, because antibiotics were adopted as "wonder drugs," they were often used in indiscriminate and improper ways. Resistant strains of bacteria began to emerge. Today, roughly fifty years after antibiotics were introduced, antibiotic resistance is a serious problem and antibiotics are losing their effectiveness. In health facilities, epidemics of antibiotic-resistant infections are serious threats to those whose health is already compromised. Diseases such as tuberculosis, once felt to be under control, are often resistant to many antibiotics and frequently do not respond to treatment. Public concern about infection has been heightened; people are once again afraid of "germs." One response to this fear is greater public use of a variety of antibacterial agents designed to remove disease-causing organisms from external surfaces before they can enter the body. Although first introduced into soaps, detergents and other cleaning and health care products, today antibacterials may also be impregnated into sponges, cutting boards, carpeting, upholstery, and even children's toys.
Using antibacterial agents to destroy many organisms before they enter the body may not always be the best way to stop the spread of infectious disease. This is because we need "good" bacteria to control and compete with "bad" bacteria. We frequently encounter and touch disease-causing or "bad" organisms (as, for example when we touch the nose, the mouth, an open wound, or fecal matter—all sources of infectious agents). However, these bacteria must compete for space with the variety of "good" bacteria that we also carry on and in our bodies and that we encounter in the environment. This means that not all contacts we have with bacteria, even "bad" bacteria, result in disease. If we destroy all the bacteria on a surface, we will destroy both kinds, removing the "good" bacteria along with the "bad". Chemical agents don't discriminate between "good" and "bad" bacteria, and can remove all bacteria. However, if bacteria do remain, these may be resistant to the effects of the chemical agents.
In certain settings, antibacterial agents are essential to fight against infection. However, if used too frequently and indiscriminately, certain antibacterial agents—those that leave trace chemical residues and that target particular processes in the life cycle of bacteria—may, like antibiotics, select for resistant strains. To insure that these agents continue to be effective when they are needed, products containing these antibacterials should only be used when they are essential to fight against infection. In other situations, when more information is not available, it is wiser to disinfect with agents that are unlikely to select for resistant strains of bacteria.
Generally, the best way to remove "bad" bacteria is through good hand-washing practice using a non-bactericidal soap and water. Proper hand-washing will remove 99.9% of bacteria, and normally, few other control measures are needed. When susceptible populations are likely to be exposed to "bad" bacteria, other more effective control measures may be required. Settings involving susceptible populations: young children, the elderly, or those whose health is compromised because of AIDS infection, use of immunosuppressive drugs, illnesses requiring hospitalization, or chemotherapy require additional disinfection measures. Antibacterial agents should be reserved for these settings.
FAQs: Antibiotic Agents
What is an antibacterial and how are antibacterials classified?
In its broadest definition, an antibacterial is an agent that interferes with the growth and reproduction of bacteria. While antibiotics and antibacterials both attack bacteria, these terms have evolved over the years to mean two different things. Antibacterials are now most commonly described as agents used to disinfect surfaces and eliminate potentially harmful bacteria. Unlike antibiotics, they are not used as medicines for humans or animals, but are found in products such as soaps, detergents, health and skincare products and household cleaners.
What are some common antibacterials?
Antibacterials may be divided into two groups according to their speed of action and residue production: The first group contains those that act rapidly to destroy bacteria, but quickly disappear (by evaporation or breakdown) and leave no active residue behind (referred to as non-residue-producing). Examples of this type are the alcohols, chlorine, peroxides, and aldehydes. The second group consists mostly of newer compounds that leave long-acting residues on the surface to be disinfected and thus have a prolonged action (referred to as residue-producing). Common examples of this group are triclosan, triclocarban, and benzalkonium chloride. See the Table of Antibacterials.
How common are antibacterials in consumer products?
All products that claim to kill bacteria and/or viruses have some kind of antibacterial agent. Alcohols, chlorine and peroxides have been used for many decades in health-care and cleaning products. Within the past two decades, the residue-producing antibacterials, once used almost exclusively in health care institutions, have been added to increasing numbers of household products, particularly soaps and cleaning agents. A recent survey reported that 76% of liquid soaps from 10 states in the US contained triclosan and approximately 30% of bar soaps contained triclocarban. Many cleaning compounds contain quaternary ammonium compounds. Because these compounds have very long chemical names, they are often not easily recognized as antibacterial agents on packaging labels. More recently, triclosan has been bonded into the surface of many different products with which humans come into contact, such as plastic kitchen tools, cutting boards, highchairs, toys, bedding and other fabrics.
Is the use of antibacterial agents regulated in the US?
Whether or not an antibacterial agent is regulated depends upon its intended use and its effectiveness. The US Food and Drug Administration (FDA) regulates antibacterial soaps and antibacterial substances that will either be used on the body or in processed food, including food wrappers and agents added to water involved in food processing.
If a substance is not intended for use on or in the body, it is registered by the US Environmental Protection Agency (EPA) under the Federal Insecticide, Fungicide, and Rodenticide Act. Substances are registered either as public health or as non-public health antimicrobial agents.
What is the difference between bacteriostats, sanitizers, disinfectants and sterilizers?
The EPA classifies public health antimicrobials as bacteriostats, sanitizers, disinfectants and sterilizers based on how effective they are in destroying microorganisms. Bacteriostats inhibit bacterial growth in inanimate environments. Sanitizers are substances that kill a certain percentage of test microorganisms in a given time span. Disinfectants destroy or irreversibly inactivate all test microorganisms, but not necessarily their spores. Sterilizers destroy all forms of bacteria, fungi, and other microorganisms and their spores.
Disinfectants can be further categorized as broad or limited spectrum agents. A broad-spectrum disinfectant destroys both gram-negative and gram-positive bacteria. A limited-spectrum disinfectant must clearly specify the specific microorganisms against which it works.
How beneficial are antibacterials?
Antibacterials are definitely effective in killing bacteria, however, there is considerable controversy surrounding their health benefits. The non-residue producing agents have been used for many years and continue to be effective agents for controlling disease organisms in a wide variety of healthcare and domestic settings. When used under strict guidelines of application, the residue-producing agents have proven effective at controlling bacterial and fungal infection in clinical settings such as hospitals, nursing homes, neonatal nurseries and other health care facilities where there may be a high risk of infection.
A certain few consumer products have demonstrated effectiveness for specific conditions: antibacterial toothpaste helps control periodontal (gum) disease; antibacterial deodorants suppress odor-causing bacteria, and anti-dandruff shampoos help control dandruff. However, to date, there is no evidence to support claims that antibacterials provide additional health benefits when used by the general consumer.
Are antibacterial agents safe?
When used as directed for external surfaces, antibacterial agents are considered to be relatively non-toxic. However, some may cause skin and eye irritation, and all have the potential for doing harm if not stored or used properly. Furthermore, evaluations of risk are based on single agents, and do not consider the effects of multiple uses or multiple compounds. Recently, triclosan has been reported in surface waters, sewage treatment plants, the bile of fish, and breast milk, but the significance of these findings is presently unknown.
Do antibacterials create resistant bacteria?
Because of their rapid killing effect, the non-residue producing antibacterial agents are not believed to create resistant bacteria. Resistance results from long-term use at low-level concentrations, a condition that occurs when consumer use residue-producing agents such as triclosan and triclocarban. Until recently, it was accepted that these agents did not affect a specific process in bacteria, and because of this, it was unlikely that resistant bacteria could emerge. However, recent laboratory evidence indicates that triclosan inhibits a specific step in the formation of bacterial lipids involved in the cell wall structure. Additional experiments found that some bacteria can combat triclosan and other biocides with export systems that could also pump out antibiotics. It was demonstrated that these triclosan-resistant mutants were also resistant to several antibiotics, specifically chloramphenicol, ampicillin, tetracycline and ciprofloxacin.
Resistance to antibacterials has been found where these agents are used continuously (as in the hospital and food industry); however, at the present time, this modest increase in resistance has not yet created a clinical problem.
Can the widespread use of antibacterial agents lead to more resistant bacteria?
Many scientists feel that this is a potential danger, but others argue that the laboratory conditions used in the research studies do not represent the "real world." So far, studies of antibacterial use in home products such as soap, deodorant and toothpaste have not shown any detectable development of resistance. However, such products have only been in use for a relatively short period of time and studies of their effects are still extremely limited.
Are there other concerns about the use of antibacterial agents?
Yes, experts believe that the use of these agents creates a false sense of security that may cause individuals to become lax in their hygiene habits. Antibacterial use should not be considered an alternative to normal hygiene, except where normal hygiene practices are impossible.
It should always be remembered that most bacteria are harmless and in many cases, even beneficial. Very few bacteria actually cause disease. Antibacterials are not discriminating and an all-out attack on bacteria in general is unjustified. Constant use of disinfecting agents tends to disrupt the normal bacteria that act as barriers against invading pathogens. This may cause shifts in bacterial populations and create a "space" for disease-causing bacteria to enter and establish infection.
In addition, some scientists have gathered evidence showing that overly hygienic homes during early childhood may be linked to the appearance of allergies later in life. In this "hygiene hypothesis," allergies develop because the childhood immune system fails to mature properly due to lack of contact with immune-stimulating bacteria. This hypothesis remains controversial and requires further research for validation.
Are there other effective cleaning methods to prevent disease spread?
For most purposes, washing with regular soap and rinsing with running water, followed by thorough drying is still considered the most important way of preventing disease transmission (see Hand washing). This is especially important after using the toilet, changing a diaper, emptying a diaper pail, cleaning the toilet, or after handling raw meat or poultry. Several common traditional agents are effective against a wide range of disease-causing organisms. These include 70% solutions of ethyl or isopropyl alcohol, household bleach and hydrogen peroxide. Unlike triclosan and other long-acting agents, these products destroy multiple cells components at once rather than attacking a specific bacterial process.
When are antibacterials useful?
While there is no evidence that the routine use of antibacterials confer a health benefit, they are useful where the level of sanitation is critical and additional precautions need to be taken to prevent spread of disease. Thus, they are important in hospitals, day care centers and healthcare facilities and other environments with high concentrations of infectious bacteria. In the home environment, they may be needed for the nursing care of sick individuals with specific infections, or for those whose immune systems have been weakened by chronic disease, chemotherapy or transplants. Under these circumstances, antibacterials should be used according to protocol, preferably under the guidance of a health care professional.