What is meant when a bacterium is said to become resistant to an antibiotic?

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.

Antibiotics are designed to fight bacteria by targeting specific parts of the bacteria’s structure or cellular machinery. However, over time, bacteria can defeat antibiotics in the following ways:

Survival of the Fittest (Natural Selection)

When bacteria are initially exposed to an antibiotic, those most susceptible to the antibiotic will die quickly, leaving any surviving bacteria to pass on their resistant features to succeeding generations.

Biological Mutations

Since bacteria are extremely numerous, random mutation of bacterial DNA generates a wide variety of genetic changes. Through mutation and selection, bacteria can develop defense mechanisms against antibiotics. For example, some bacteria have developed biochemical “pumps” that can remove an antibiotic before it reaches its target, while others have evolved to produce enzymes to inactivate the antibiotic.

DNA Exchange

Bacteria readily swap bits of DNA among both related and unrelated species. Thus, antibiotic-resistant genes from one type of bacteria may be incorporated into other bacteria. As a result, using any one antibiotic to treat a bacterial infection may result in other kinds of bacteria developing resistance to that specific antibiotic, as well as to other types of antibiotics.

Rapid Reproduction

Bacteria reproduce rapidly, sometimes in as little as 20 minutes. Therefore, it does not take long for the antibiotic-resistant bacteria to comprise a large proportion of a bacterial population.

Antibiotic-Resistant Bacteria and Effectiveness of Those Drugs

To date, all antibiotics have over time lost effectiveness against their targeted bacteria. The earliest antibiotics were developed in the 1940s.

These "miracle drugs" held at bay such devastating diseases as pneumonia and tuberculosis, which had previously been untreatable. But the steady evolution of resistant bacteria has resulted in a situation in which, for some illnesses, doctors now have only one or two drugs “of last resort” to use against infections by superbugs resistant to all other drugs. For example:

Staph Aureus

Nearly all strains of Staphylococcus aureus in the United States are resistant to penicillin, and many are resistant to newer methicillin-related drugs. Since 1997, strains of S. aureus have been reported to have a decreased susceptibility to vancomycin, which has been the last remaining uniformly effective treatment.

Campylobacter Infections

Today, one out of six cases of Campylobacter infections, the most common cause of food borne illness, is resistant to fluoroquinolones (the drug of choice for treating food-borne illness). As recently as ten years ago, such resistance was negligible.

Next Steps

Clearly, it is important to extend the useful lifetime of any drug that is effective against human disease. And today, this is even more important because few new antibiotics are being developed, and those that are developed tend to be extremely expensive.

What happens if you are resistant to antibiotics?

What does antibiotic resistance mean quizlet?