Antibiotics - Part 1

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INTRODUCTION
In modern usage, An antibiotic is a chemotherapeutic agent with activity against microorganisms such as bacteria, fungi or protozoa. The term "antibiotic" was coined by Selman Waksman in 1942 to describe any substance produced by a micro-organism that is antagonistic to the growth of other micro-organisms in high dilution. This original definition excluded naturally occurring substances, such as gastric juice and hydrogen peroxide (they kill micro-organisms but are not produced by micro-organisms), and also excluded synthetic compounds such as the sulfonamides (which are antimicrobial agents). Many antibiotics are relatively small molecules with a molecular weight less than 2000 Da. With advances in medicinal chemistry, most antibiotics are now modified chemically from original compounds found in nature, as is the case with beta-lactams (which include the penicillins, produced by fungi in the genus Penicillium, the cephalosporins, and the carbapenems). Some antibiotics are still produced and isolated from living organisms, such as the aminoglycosides; in addition, many more have been created through purely synthetic means, such as the quinolones.

OVERVIEW

Unlike previous treatments for infections, which often consisted of administering chemical compounds such as strychnine and arsenic, with high toxicity also against mammals, antibiotics from microbes had no or few side effects[citation needed] and high effective target activity. Most anti-bacterial antibiotics do not have activity against viruses, fungi, or other microbes. Anti-bacterial antibiotics can be categorized based on their target specificity: "narrow-spectrum" antibiotics target particular types of bacteria, such as Gram-negative or Gram-positive bacteria, while broad-spectrum antibiotics affect a wide range of bacteria.
The environment of individual antibiotics varies with the location of the infection, the ability of the antibiotic to reach the site of infection, and the ability of the microbe to inactivate or excrete the antibiotic. Some anti-bacterial antibiotics destroy bacteria (bactericidal), whereas others prevent bacteria from multiplying (bacteriostatic).
Oral antibiotics are simply ingested, while intravenous antibiotics are used in more serious cases, such as deep-seated systemic infections. Antibiotics may also sometimes be administered topically, as with eye drops or ointments.
In the last few years three new classes of antibiotics have been brought into clinical use. This follows a 40-year hiatus in discovering new classes of antibiotic compounds. These new antibiotics are of the following three classes: cyclic lipopeptides (daptomycin), glycylcyclines (tigecycline), and oxazolidinones (linezolid). Tigecycline is a broad-spectrum antibiotic, while the two others are used for Gram-positive infections. These developments show promise as a means to counteract the growing bacterial resistance to existing antibiotics.
Although potent antibiotic compounds for treatment of human diseases caused by bacteria (such as tuberculosis, bubonic plague, or leprosy) were not isolated and identified until the twentieth century, the first known use of antibiotics was by the ancient Chinese over 2,500 years ago. Many other ancient cultures, including the ancient Egyptians, ancient Greeks and medieval Arabs already used molds and plants to treat infections, owing to the production of antibiotic substances by these organisms, a phenomenon known as antibiosis.
Quinine became widely used as a therapeutic agent in the 17th century for the treatment of malaria, the disease caused by Plasmodium falciparum, a protozoanparasite.
Antibiosis was first described in 1877 in bacteria when Louis Pasteur and Robert Koch observed that an airborne bacillus could inhibit the growth of Bacillus anthracis. to the discovery of penicillin,The antibiotic properties of Penicillium sp. were first described in england by John Tyndall in 1875.However, his work went by without much notice from the scientific community until Alexander Fleming's discovery of Penicillin.
Modern research on antibiotic therapy began in Germany with the development of the narrow-spectrum antibiotic Salvarsan by Paul Ehrlich in 1909, for the first time allowing an efficient treatment of the then-widespread problem of Syphilis. The drug, which was also effective against other spirochaeta infections, is no longer in use in modern medicine.
Antibiotics were further developed in Britain following the discovery of Penicillin in 1928 by Alexander Fleming. More than ten years later, Ernst Chain and Howard Florey, Baron Florey|Howard Florey became interested in his work, and came up with the purified form of penicillin. The three shared the 1945 Nobel Prize in Medicine. In 1939, Rene Dubos isolated gramicidin, one of the first commercially manufactured antibiotics in use during World War II to prove highly effective in treating wounds and ulcers.
Prontosil, the first commercially available antibacterial antibiotic was developed by a research team led by Gerhard Domagk (who received the 1939 Nobel Prize in Physiology or Medicine for his efforts at the Bayer Laboratories of the IG Farben conglomerate in Germany. Prontosil had a relatively broad effect against Gram-positive Coccus but not against Enterobacteriaceae. The discovery and development of this first Sulfonamide drug opened the era of antibiotics.

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