America in the 1940s brimmed with an infectious enthusiasm and reckless confidence that nothing existed that could not be conquered, including disease. All the world embraced the new generation of wonder drugs called antibiotics. The antibiotic era was ushered in as diseases such as tuberculosis and pneumonia fell in ignominious defeat to the all-powerful drugs.
Today the world faces a serious resurgence of infectious diseases. The bacterium that causes tuberculosis (TB), a disease once thought to be annihilated in industrialized nations, now exists in forms resistant to as many as seven different antibiotics, rendering it virtually untreatable. Many other bacteria also have developed antibiotic resistances. Scientists face the challenge of discovering how to deal with diseases that do not respond to the latest high-tech drugs.
Biology professor Bruce Levin and his colleagues at Emory are looking into this problem from an ecologist's point of view. Levin feels that the evolution of antibiotic resistance in bacteria provides the perfect opportunity to study classic ecological questions. The information gained from asking these basic questions in this system could provide much insight into the phenomena of natural selection and survival of the fittest. The generation time of the bacteria is quick, especially compared to trees and other organisms, which are most often the subject of ecological competition studies, and the experiments can be performed in the lab, eliminating costly travel to field sites. Levin hopes that this research will help to answer some classical questions in biology as well as provide practical information about infectious diseases and the most effective ways to combat them.
Levin and many other scientists are concerned about the casual attitude of society toward the use of antibiotics. Feed for livestock often contains broad spectrum antibiotics, and antibiotics are routinely sprayed on fruit trees to prevent blemishes. This type of unnecessary use puts more antibiotics into the environment, providing ideal conditions for natural selection of organisms resistant to the drugs. Levin notes that another major problem with antibiotic use stems from society's "give me a pill and make me feel better" attitude. People would prefer to take a pill and keep on doing whatever they are doing, when bed rest and lots of fluids might be the best course of action. Physicians and patients alike assume there are no harmful effects from taking antibiotics.
That assumption may not be true. For instance, when a cold is treated with broad spectrum antibiotics "to prevent a secondary bacterial infection," the treatment may significantly increase the chances that the individual will be infected by bacteria resistant to the drug. The antibiotic kills off the normal flora (good bacteria), which usually compete with the pathogens (bad bacteria) for essential nutrients. This competition serves as an important method of defense against illness in healthy people. In this case, the use of antibiotics gives the resistant pathogen much greater chances of invading the host (person), because no other bacteria have survived to compete with it. The end result is that the pathogen invades and grows quickly, perhaps too quickly for the person's immune system (natural defenses) to respond.
Levin chaired the "Emergence and Reemergence of Infectious Disease Symposium" at the American Association for the Advancement of Science meeting in Atlanta last month. His talk at the symposium focused on alternatives to antibiotics for the control of infectious diseases. Among alternative treatments being researched are microbial interference, stopping infection by using non-pathogenic bacteria as competitors of pathogens; serum therapy or passive immunization, using antibodies made against an organism to give the host's immune system time to respond to the infection; and phage therapy, using viruses that specifically infect bacteria to kill pathogens. All of these alternatives had been researched before the advent of antibiotics, but the immediate success of antibiotics eclipsed this work.
These alternatives have some practical drawbacks too. They all have very narrow targets, so one phage or serum is not going to be effective against multiple species of bacteria. Using these techniques will require the exact identification of the strain of bacteria involved in the infection. Additionally, the cost of developing therapies that have narrow targets may well outweigh the potential profits, so commercializing these alternatives will be difficult.
However, these alternatives may prove useful. Levin and colleagues isolated a strain of bacteria phage from the Atlanta sewage treatment plant that is as effective as streptomycin in the treatment of acute infections of bacteria in mice. Microbial interference also has proven valuable in the treatment of antibiotic-associated colitis, a gut infection that is a side effect of antibiotic treatment. The infection is caused by Clostridium dificile, a relative of the botulism and tetanus-causing bacteria. It colonizes the gut and causes disease when normal flora have been killed off by antibiotics.
Levin predicts that there probably will not be a miracle cure to replace antibiotic therapy. He strongly advises implementing more prudent use of antibiotics now and taking a hard look at the evolution of resistance to any alternative therapies that are used in the future.
-- Michele Arduengo