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The Gale Encyclopedia of Science. 5th ed. 2014. Lexile Measure: 1280L. Updated: Oct. 31, 2017
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Antibiotics are natural or synthetic compounds that kill bacteria. There are a myriad of different antibiotics that act on different structural or biochemical components of bacteria. Antibiotics have no direct effect on viruses.

Prior to the discovery of the first antibiotic, penicillin, in the 1930s, there were few effective ways of combating bacterial infections. Illnesses such as pneumonia, tuberculosis, and typhoid fever were virtually untreatable, and minor bacterial infections could blossom into life-threatening maladies. In the decades following the discovery of penicillin, scientists discovered many naturally occurring antibiotics and still more were synthesized towards specific targets on or in bacteria.

Antibiotics are manufactured by bacteria and various eukaryotic organisms, such as plants, usually to protect the organism from attack by other bacteria. The discovery of these compounds involves screening samples of bacteria for an inhibition in growth of the bacteria. In commercial settings, such screening has been automated so that thousands of samples can be processed each day. Antibiotics also can be manufactured by tailoring a compound to hone in on selected targets. The advent of molecular sequencing technology and three-dimensional image reconstruction facilitates new antibiotic design.

Penicillin is one of the antibiotics in a class known as beta-lactam antibiotics. This class is named for the ring structure that forms part of the antibiotic molecule. Other classes of antibiotics include the tetracyclines, aminoglycosides, rifamycins, quinolones, and sulphonamides. The action of these antibiotics is varied. For example, beta-lactam antibiotics exert their effect by disrupting the manufacture of peptidoglycan, which is the main stress-bearing network in the bacterial cell wall. The disruption can occur by either blocking construction of the subunits of the peptidoglycan or preventing their incorporation into the existing network. In another example, amonglycoside antibiotics can bind to a subunit of the ribosome, which blocks the manufacture of protein or reduces the ability of molecules to move across the cell wall to the inside of the bacterium. As a final example, the quinolone antibiotics disrupt the function of an enzyme that uncoils the double helix of deoxyribonucleic acid, which is vital if the DNA is to be replicated.

Besides being varied in their targets for antibacterial activity, antibiotics also can vary in the range of bacteria they affect. Some antibiotics are classified as narrow-spectrum antibiotics. They are lethal against only a few types (or genera) of bacteria. Other antibiotics are active against many bacteria whose construction can be very different. Such antibiotics are described as having a broad-spectrum of activity.

In the decades following the discovery of penicillin, a myriad of different antibiotics proved to be phenomenally effective in controlling infectious bacteria. Antibiotics quickly became (and to a large extent remain) a vital tool in the physician's arsenal against many bacterial infections. Indeed, by the 1970s, the success of antibiotics led to the generally held view that bacterial infectious diseases would soon be eliminated. However, the subsequent emergence of antibiotic resistant bacteria to many commonly administered antibiotics has challenged this idea.

Antibiotic resistance develops when antibiotics are overused or misused. If an antibiotic is used properly to treat an infection, then all the infectious bacteria should be killed directly or weakened such that the host’s immune response will kill them. However, using an antibiotic that is not strong enough or stopping antibiotic therapy before the prescribed time period can leave surviving bacteria in the population. These surviving bacteria have demonstrated resistance.

With effective antimicrobials continuing to dwindle in number and effectiveness, in September 2014, scientists advanced the idea of amplifying natural antibiotics the human body manufactures in very small quantities. In a study published in the journal Cell, researchers identified genes and combinations of genes containing the coding for thousands of molecules that might prove useful antibiotics.

Resistance to an antibiotic also can be overcome by modifying the antibiotic slightly via addition of a different chemical group. This acts to alter the structure of the antibiotic. Unfortunately, such a modification tends to produce susceptibility to the new antibiotic in a relatively short time.

If the resistance is governed by a genetic alteration, the genetic change may be passed on to subsequent generations of bacteria. For example, many strains of the bacterium that causes tuberculosis have become also resistant to one or more of the antibiotics routinely used to control the lung infection. As a second example, some strains of Staphylococcus aureus, which can cause boils, pneumonia, or bloodstream infections, are resistant to almost all antibiotics, making those conditions difficult to treat. Methicillin-resistant Staphylococcus aureus (MRSA) is a resistant infection that has been found in hospitals, care facilities, gyms, and other locations. Recent studies indicate that compared with methicillin-resistantÿvariant (MRSA) carriers, carriers of methicillin-susceptibleÿ Staphylococcus aureusÿ(MSSA) are less likely to acquire MRSA while hospitalized. Physicians caution that antibiotic over-prescription, especially the administering of antibiotics for viral conditions over which they have no effect, is decreasing the effectiveness of many common and inexpensive antibiotics.

In January 2015, scientists at Northeastern University in Boston, Massachusetts, announced a new way to grow soil-based bacteria that in turn helps scientists produce new types of antibiotics. The last such fundamental discovery of classes of antibiotics took place in the late 1980s. Publishing in the journal Nature, the researchers articulated new techniques to increase the percentage of soil-based bacteria that can be grown in laboratory conditions. Growing a wider variety of bacteria that already exist greatly increases the chances of isolating new natural antibiotics.

Experts in the public health perils created by increasing antibiotic resistance heralded the breakthrough as a potential game changer. Tempering expectations, however, other researchers noted that the new antibiotics have yet to undergo comprehensive human testing and that the antibiotics produced thus far work only against Gram-positive bacteria (including MRSA and mycobacterium tuberculosis). By February 2105, none of the new antibiotics reported could penetrate the extra layer of protection found in Gram-negative bacteria (including E. coli).

Source Citation   (MLA 8th Edition)
Hoyle, Brian. "Antibiotics." The Gale Encyclopedia of Science, edited by K. Lee Lerner and Brenda Wilmoth Lerner, 5th ed., Gale, 2014. Science In Context, Accessed 17 Feb. 2019.

Gale Document Number: GALE|CV2644030127