Antibiotics block the life cycle of bacteria that invade the human body. The first of these antibiotics, penicillin, works by blocking the molecules that construct the cell walls of particular bacteria. The bacteria, with incomplete cell walls, are not able to reproduce.
When penicillin was introduced during World War II, it was truly a "miracle drug." Until that time, anyone who was cut or wounded stood a great risk of infection. Once penicillin became available, the situation changed. Wounded soldiers, children with ear infections, and many others began to benefit from the ability to block the growth of bacteria.
While humanity may have won that particlar battle against bacteria, the war is far from over. The reason is that in any bacterial population, there are bound to be a few bacteria that, for one reason or another, are not affected by a particular antibiotic. For example, they may have a slightly differently shaped enzyme that builds cell walls, so that penicillin will not fit onto that particular shape of the enzyme. These bacteria will not be affected by that particular drug.
For that small group, the antibiotic is a real godsend. It doesn't affect them, but it does wipe out all of their competition. They are thus free to multiply, and, over time, all of the bacteria will have whatever properties that made those individuals resistant.
Traditionally, medical scientists have dealt with this phenomenon by developing a large number of antibiotics, each of which intervenes in the bacterial life cycle in a slightly different way. Consequently, if you happen to have a bacterium that is resistant to one antibiotic, probably it will succumb to the action of another. You may, in fact, have had the experience of going to a doctor with an infection, being given an antibiotic, and then finding that it didn't work. In all likelihood, all your doctor had to do then was prescribe a different antibiotic and everything was fine.
The problem is that as time has passed, more and more bacteria have become resistant to antibiotics. In fact, currently, there is one strain of bacteria- Staphylococcus-that is resistant to every commercially available antibiotic except one, and in 1996, a bacterium with lowered resistance to that last antibiotic appeared in Japan.
The appearance of drug-resistant bacteria is not particularly surprising; in fact, it probably should have been anticipated. Nevertheless, in the late 1980s, there was a general sense of complacency among scientists on the antibiotic question. Little profit was to be made by developing the one-hundred-and-first antibiotic. Drug companies concentrated their efforts on other areas. Therefore, a gap developed between the production of new antibiotics and the development of resistance among bacteria.
By the early 1990s, this gap was recognized and highlighted in several national news magazines. More companies returned to develop new kinds of antibiotics, and currently, a number are undergoing clinical trials. By early in the twenty-first century, some of these new drugs will start to come on the market, and the problem will be "solved," at least for the moment.
Additional research will focus on the processes by which cells repair the constant damage to DNA, but the computer design of new drugs, the development of new antibiotics, and techniques to combat bacteria should remain a top priority.
A. They interfere with the reproductive cycle of bacteria.
B. They construct cell walls to resist bacteria.
C. They inject enzymes that explode in affected cells.
D. They increase the mitosis of healthy cells
32.The word “them” in paragraph 4 refers to
A.whatever properties
B. resistant bacteria
C. their competition
D. those individuals