listen to part of a lecture in a microbiology class.

P: last week, we discussed how the discovery of penicillin in 1928 gave rise to the age of antibiotics. Antibiotics became the medication of choice for treating bacterial infections. Bacteria, as you'll recall, are single celled organisms. How does penicillin stop a bacterium from growing? S: It prevents the bacterium from building its cell wall, the thin barrier that protects the organism. P: Good. We also talked about other antibiotics that work by targeting the proteins that bacteria rely on to reproduce. Bacteria generally have a short lifespan, so if we can prevent their reproduction, the bacteria in an area are soon gone. But increasingly, we're finding bacteria that are resistant to antibiotics, that don't respond to antibiotic treatment.

Now this is a natural phenomenon and not altogether unexpected, and that's because organisms mutate. That is, their genetic structure changes randomly. Sometimes those random changes create traits that help an organism survive. When that happens, the traits tend to get passed on to future generations, so say, a random change in the bacterium allows it to overcome an antibiotic. This new form of the bacteria will reproduce in the presence of the antibiotic, while other bacteria die off. Soon the new resistant form becomes the dominant strain of bacteria in that area. This natural process has been aided to some extent by the overuse of antibiotics. The more we use antibiotics, the more opportunity there is for resistant strains of bacteria to emerge, which is why many doctors are now cautious when prescribing antibiotics.

So how does the resistance to antibiotics work? One of the most successful forms of resistance has to do with enzymes. Enzymes are special proteins that speed up chemical reactions. Bacteria produce enzymes and sometimes genetic mutations cause them to produce new enzymes, including enzymes that attack antibiotic molecules and break them down.

Another form of resistance has to do with bacteria's structure. For example, we saw that penicillin destroys bacteria by destroying their cell walls, but if the chemical structure of the cell wall has changed, then the penicillin may no longer be effective. A third form of resistance involves something called molecular pumps. A molecular pump is a special structure that can transport molecules out of the cell. If an antibiotic enters a bacterium, a mutated pump could send it back outside the cell, preventing the antibiotic from reaching its target.

So what can be done to overcome these mechanisms of antibiotic resistance? Well, since we know the resistance comes about through genetic changes, we can counteract it through genetically designed antibiotic solutions. For example, researchers have identified the gene in bacteria that prevents penicillin from damaging bacterial cell walls. Most importantly, they found that the gene can be chemically deactivated. In other words, there are chemicals that will stop this new gene from functioning properly.

This opens up an interesting possibility. First, remove the penicillin resistance by turning off the new gene. Then follow that up with penicillin to destroy the bacteria. We might call this combination therapy. One of the benefits of this combination therapy is that we don't have to develop a whole new range of antibiotics after the new gene has been disabled. We can use the same penicillin we've always used.

Some researchers have taken a different approach to finding ways to fight resistant bacteria. They decided to look for an answer in nature, and that's not a bad idea, because nature sometimes comes up with solutions that are far superior to anything we can think of ourselves. For example, the naturally occurring viruses that are called phages. In nature, phages are a type of virus that target and destroy specific bacteria, and because phages already exist, we don't need to spend time and expense to develop them. Phages are also highly adaptable.

As bacteria evolve, so do phages. In theory, this means it should be impossible for bacteria to become totally resistant to phages. But the great challenge with phages is that they're highly specific about which bacteria they target. This means we need to find and catalog a different phage for every different type of bacterium, which is no easy task.