Antibiotic resistance in bacteria well explained

Alexander Fleming, a Scottish scientist, is credited with discovering the first antibiotic, penicillin. In 1928, he noticed that bacteria could not survive on a plate that contained a mold commonly found on bread. He went on to show that the effect was due to a diffusible substance made by the mold. However, penicillin was not available to the general public until the early 1940s when scientists learned how to produce and purify large amounts of penicillin.

In fact, technically speaking, Fleming may have rediscovered a substance that had been found before. In 1896, the French medical student Ernest Duchesne showed antibiotic properties of the mold Penicillium, but did not report a connection between the fungus and a substance that had antibacterial properties. Penicillium was unknown to the scientific community until Fleming discovered the phenomenon and the substance, and named it penicillin.

In 1895, there was a report by an Italian researcher, Vincenzo Tiberio, describing a natural substance from molds which had antibacterial properties resembling penicillin. Yet another report describes a professor at John Hopkins University in Baltimore who showed his students an agar plate with a mold which inhibited bacterial growth. (Levy, S.B. The Antibiotic Paradox. How Misuse of Antibiotics Destroys Their Curative Powers. Perseus Books, 2002). So perhaps others had seen and described the phenomenon, but Fleming was the first to bring such a substance to wide scientific attention.

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About Antibiotic Resistance

What is antibiotic resistance?

Antibiotic resistance occurs when an antibiotic has lost its ability to effectively control or kill bacterial growth; in other words, the bacteria are "resistant" and continue to multiply in the presence of therapeutic levels of an antibiotic.

Why do bacteria become resistant to antibiotics?

Antibiotic resistance is a natural phenomenon. When an antibiotic is used, bacteria that can resist that antibiotic have a greater chance of survival than those that are "susceptible." Susceptible bacteria are killed or inhibited by an antibiotic, resulting in aselective pressure for the survival of resistant strains of bacteria.

Some resistance occurs without human action, as bacteria can produce and use antibiotics against other bacteria, leading to a low-level of natural selection for resistance to antibiotics. However, the current higher-levels of antibiotic-resistant bacteria are attributed to the overuse and abuse of antibiotics. In some countries and over the Internet, antibiotics can be purchased without a doctor's prescription. Patients sometimes take antibiotics unnecessarily, to treat viral illnesses like the common cold.

How do bacteria become resistant?

Some bacteria are naturally resistant to certain types of antibiotics. However, bacteria may also become resistant in two ways: 1) by a genetic mutation or 2) by acquiring resistance from another bacterium.

Mutations, rare spontaneous changes of the bacteria's genetic material, are thought to occur in about one in one million to one in ten million cells. Different genetic mutations yield different types of resistance. Some mutations enable the bacteria to produce potent chemicals (enzymes) that inactivate antibiotics, while other mutations eliminate the cell target that the antibiotic attacks. Still others close up the entry ports that allow antibiotics into the cell, and others manufacture pumping mechanisms that export the antibiotic back outside so it never reaches its target.

Bacteria can acquire antibiotic resistance genes from other bacteria in several ways. By undergoing a simple mating process called "conjugation," bacteria can transfer genetic material, including genes encoding resistance to antibiotics (found on plasmids and transposons) from one bacterium to another. Viruses are another mechanism for passing resistance traits between bacteria. The resistance traits from one bacterium are packaged into the head portion of the virus. The virus then injects the resistance traits into any new bacteria it attacks. Bacteria also have the ability to acquire naked, "free" DNA from their environment.

Any bacteria that acquire resistance genes, whether by spontaneous mutation or genetic exchange with other bacteria, have the ability to resist one or more antibiotics. Because bacteria can collect multiple resistance traits over time, they can become resistant to many different families of antibiotics.

How does antibiotic resistance spread?

Genetically, antibiotic resistance spreads through bacteria populations both "vertically," when new generations inherit antibiotic resistance genes, and "horizontally," when bacteria share or exchange sections of genetic material with other bacteria. Horizontal gene transfer can even occur between different bacterial species. Environmentally, antibiotic resistance spreads as bacteria themselves move from place to place; bacteria can travel via airplane, water and wind. People can pass the resistant bacteria to others; for example, by coughing or contact with unwashed hands.

Can bacteria lose their antibiotic resistance?

Yes, antibiotic resistance traits can be lost, but this reverse process occurs more slowly. If the selective pressure that is applied by the presence of an antibiotic is removed, the bacterial population can potentially revert to a population of bacteria that responds to antibiotics.

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Multiple-drug resistance

Sometimes bacteria find a way to fight the antibiotic you are taking and your infection won't go away. When antibiotic resistance develops, your doctor must prescribe a different antibiotic in order to fight the infection. Multiple-drug resistance occurs when bacteria are resistant to more than one antibiotic. Because of years of antibiotic overuse, multidrug resistance is now the rule rather than the exception among resistant bacteria. This situation has largely occurred through the sequential use of multiple different antibiotics. The first antibiotic began by selecting a single resistance gene. Eventually, however, bacteria resistant to the first antibiotic picked up resistance to others as they were introduced into the environment. It's like a snowball rolling downhill, becoming bigger and stronger and not losing what it had acquired before.

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Antibiotic Resistance, A Societal Problem

How can antibiotic resistance harm humans?

If large numbers of bacteria are resistant to antibiotics, it will be more difficult and more expensive to treat human bacterial infections. When antibiotics fail to work, consequences include extra visits to the doctor, hospitalization or extended hospital stays, a need for more expensive antibiotics to replace the older ineffective ones, lost workdays and, sometimes, death.

Why is antibiotic resistance a public health problem?

Antibiotics are called "societal drugs," since antibiotic resistance can pass from bacterium to bacterium (see About antibiotic resistance), and resistant bacterial infections can pass from person to person. Thus, antibiotic use and antibiotic resistance can eventually affect an entire community.

Why is antibiotic resistance an ecological problem?

When antibiotics are used in humans or animals, approximately 80 - 90% of the ingested antibiotics are not broken down, but pass through the body intact and enter the environment as waste. Thus, they retain their ability to affect bacteria and promote antibiotic resistance even after they enter the soil or water as a waste product.  (See APUA's fact sheet, "The Need to Improve Antibiotic Use in Food Animals")

Do people become resistant to antibiotics?

No, this is a common misconception. People may exhibit allergic reactions to antibiotics, but they are not resistant to them. It is the bacteria themselves, not the infected host, which become resistant.

How serious is the problem of antibiotic resistance?

The CDC estimates 23,000 annual U.S. deaths and $20 billion in excess direct health costs are the result of antibiotic resistance. While the real magnitude of the problem is unknown, the monetary cost of treating antibiotic resistant infections worldwide is estimated to be many billions of dollars per year. Some experts predict that, as resistance to antibiotics is increasing at a faster pace than it can be controlled, the future will resemble the pre-antibiotic era. Others are more optimistic that research and careful drug management can reverse the trend if global efforts are focused on recognizing and controlling it