Antibiotic resistance is the ability of microbes, especially certain bacteria, to overcome substances that might otherwise kill them or interfere with their growth. Since the 1940’s, scientists have developed many types of antibiotic drugs to treat diseases caused by bacteria. The development of such drugs, one of the greatest advancements in medicine, led to a dramatic reduction in human illness and death caused by infection. However, medical experts worry that bacteria are now widely resistant to existing antibiotics, while the development of new antibiotics has slowed.
In bacteria, as in other living things, genes carry the instructions that regulate life processes. Bacteria reproduce at a rapid rate, which increases the chances that a genetic mutation (change) can occur. A bacterial infection is caused by hundreds of millions, even billions, of bacteria. In any such population, some bacteria are likely to carry antibiotic-resistant traits that result from random mutations. When a person then takes antibiotics, bacteria that are not able to overcome the medicine die. The remaining bacteria are usually those that have some level of antibiotic resistance. In the absence of other bacteria, the resistant bacteria can more easily reproduce and become widespread. As antibiotic use became more common, this process has been repeated many times. Some varieties of bacteria are resistant to several antibiotic drugs. As scientists work to develop new types of antibiotics, bacteria are always evolving resistance.
Bacteria can be resistant to one specific antibiotic or to a group of chemically similar antibiotics, such as the penicillins. Bacteria can resist antibiotics in several different ways. In some bacteria, the makeup of the cell’s outer membrane may hinder or prevent antibiotics from entering it. Or the shape of certain proteins in the bacteria may prevent antibiotics from binding to it. Certain bacteria have proteins that act as a pump, expelling antibiotics from the cell. And some bacteria can produce enzymes that break down antibiotics before they can harm the cell. Enzymes are molecules that speed up reactions in living things. Scientists have also discovered that bacteria can acquire antibiotic resistance directly from other bacteria through the transfer of genetic material.
Antibiotic resistance has been a serious problem for many years in hospitals, where antibiotic use is widespread and infections can be passed readily between patients. However, medical experts worry that antibiotic resistance is becoming more widespread in communities. For example, penicillin-resistant strains of Streptococcus pneumoniae, a bacterium that causes a variety of illnesses in human beings, are common throughout the United States.
More powerful antibiotics may be used to treat bacterial infections that are resistant to penicillin. The use of other powerful antibiotics, however, has led to resistance in a common strain of another bacterium, called Staphylococcus aureus. Such multiple-resistant Staphylococcus aureus, often abbreviated MRSA, can cause serious illness or death. Most antibiotics are not effective against MRSA, but physicians can usually treat the infection with another powerful antibiotic called vancomycin. Scientists have discovered strains of Staphylococcus aureus that are resistant to vancomycin. They worry that if such strains become widespread, no antibiotic drugs may be effective against them. 
Medical experts cite several factors in the rise of antibiotic resistance. Physicians often prescribe antibiotics unnecessarily, and the public uses antibiotics excessively. In addition, antibacterial hand soaps and lotions are widespread and popular, but these practices and products can actually increase the number of resistant bacteria and create opportunities for new resistant varieties to develop. In hospitals and other health-care facilities, resistant varieties often spread from patient to patient due to a lack of effective infection-control procedures. Such procedures include frequent hand washing and proper disinfection of equipment. The United States Centers for Disease Control and Prevention (CDC) has developed guidelines to help prevent the development of antibiotic resistance in disease-causing bacteria. In addition, scientists continue research to develop new types of antibiotic drugs and improved infection-control methods.
See also Antibiotic; Bacteria; Penicillin (Resistance); Staphylococcus.
