The Great Arms Race against the microbe

by Rod Lievano

We, and every other living thing, exist in a constant state of war against a vastly numerous, resourceful, and implacable enemy: the microbe, AKA microorganism, bacteria, virus, fungus, mold, or just plain germ or bug.

We have many natural allies in this war, but until the discovery of disinfectants (and of germs themselves), the balance was very much in the microbes’ favor. Yet that balance is ever unstable. Conditions change, and so the fortunes of war. Human populations grow, concentrate, and move around ever more rapidly and farther, creating improved battlegrounds for microbes. Better disinfectants (antibacterials, antibiotics, vaccines, antimicrobials) are developed, only to become ineffective as microbes mutate.

In the late 1800s, recurrent outbreaks of cholera, diphtheria, and typhus triggered widespread public concern over domestic hygiene. This need nurtured invention, resulting in new technologies such as toilets, sewer traps, water treatment systems, and, eventually, vaccines, antibacterials and antibiotics.

Attack and Counter attack

Over a century later, new strains of microbes—some of them increasingly resistant to traditional antimicrobials—are again raising concerns, and again triggering the development of new technologies. According to Marketing Intelligence Service, a marketing research firm of Naples, New York, the number of new germ-fighting products has risen steadily over the past 7 years, from 36 in 1992 to 135 in 1999.

Early products in this wave of new weapons were useful, but not particularly revolutionary. The market was suddenly flooded with soaps, sprays, and creams containing antimicrobials, predominantly triclosan, a broad-spectrum germicide used for 25 years in hospital soaps. The real breakthrough, made by Microban Products Company of Huntersville, NC, was the development of a way to bond triclosan to plastic polymers, opening the way for such specialty germ-fighting products as surgical drapes, orthopedic cast liners, and hospital mattress covers, and later to a range of consumer goods like cutting boards, toothbrush holders, toys, and food containers.

But the technology naturally has some shortcomings. Although the U.S. Food and Drug Administration (FDA) has judged triclosan safe for ingestion, approving a toothpaste with triclosan, there are doubts about its effectiveness. Experts admit that triclosan probably does no harm, but point out that there have not been any extensive studies on its effectiveness to protect against infection. Furthermore, the U.S. Environmental Protection Agency (EPA, which lists all antimicrobials as pesticides), citing this lack of evidence, has admonished one toy company for making an infection-preventing claim for its triclosan-containing toys.

In any case, the question of effectiveness may be somewhat beside the point, since it is known that the triclosan (and other conventional antimicrobials) in plastics eventually wears out, and cannot be replaced.  

Sound the charge! New weapons

A new material—the first antimicrobial rubber—uses a different mechanism than conventional coatings and protective plastics. In laboratory tests, it killed viruses, fungi, and bacteria more effectively than existing antimicrobial plastics.

This new technology introduces a chemical structure called an N-halamine into the polystyrene molecules present in a variety of synthetic rubber materials. N-halamines contain a receptor that binds chlorine atoms. The microbe is killed when it comes in contact with the surface of the rubber, where it is exposed to chlorine. Although the rubber loses its antimicrobial ability once the chlorine atoms are used up, soaking the rubber in bleach can renew this feature by providing the missing chlorine atoms. Rubber formulas can be given enhanced disease-fighting power by adding more N-halamine groups to their structure.

N-halamines can also be used in a variety of other substances. HaloSource Corporation of Seattle, Wash., is proposing to commercialize the new technology in a variety of formulations including water-based liquids, synthetic rubbers, and polymers (plastics) to be used in textiles, water and air purification, healthcare products, food safety, odor control, aquaculture, disinfection, preservation, and other commercial uses.

For uses not associated with food, Dow Corning has developed Aegis Antimicrobial Technology, a substance that bonds to any surface and effectively controls bacteria, fungi (mold, mildew, and yeast), algae, and other one-celled organisms.

Because of its unique chemical bonding system, Aegis Antimicrobial Technology works by disrupting or rupturing the microorganism’s cell membrane upon direct contact with the organism. This interrupts the normal life processes and destroys the cell. Applications thus far include treatment of air purification systems, air conditioning duct systems, draperies, upholstery, floor coverings (carpets, ceramic tile, and concrete), wall coverings (paint, paper, wood), ceilings, chrome, stainless steel, fiberglass, vinyl, porcelain, marble, book covers, aluminum, and glass.

Don’t forget the old spears and clubs

Fine new technology, and welcome. But some experts (Critics? Cynics? Skeptics? Realists?) maintain that we could do just as well by merely washing our hands thoroughly with good old plain (non-triclosan) soap and water several times a day. Could we become a nation of obsessive hand-washers?