Antibiotic
<p >An <b>antibacterial</b> is a compound or substance that kills or slows down the growth of <a href="http://en.wikipedia.org/wiki/Bacteria" title="Bacteria" >bacteria</a>.<sup id="cite_ref-urlDorlands_Medical_Dictionary:antibacterial_0-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Antibiotic#cite_note-urlDorlands_Medical_Dictionary:antibacterial-0" >[1]</a></sup> The term is often used <a href="http://en.wikipedia.org/wiki/Synonym" title="Synonym" >synonymously</a> with the term <i>antibiotic(s)</i>; today, however, with increased knowledge of the causative agents of various infectious diseases, <i>antibiotic(s)</i> has come to denote a broader range of <a href="http://en.wikipedia.org/wiki/Antimicrobial" title="Antimicrobial" >antimicrobial</a> compounds, including <a href="http://en.wikipedia.org/wiki/Antifungal_medication" title="Antifungal medication" >antifungal</a> and other compounds.<sup id="cite_ref-urlDorlands_Medical_Dictionary:antibiotic_1-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Antibiotic#cite_note-urlDorlands_Medical_Dictionary:antibiotic-1" >[2]</a></sup></p>
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The term <i>antibiotic</i> was coined by <a href="http://en.wikipedia.org/wiki/Selman_Waksman" title="Selman Waksman" >Selman Waksman</a> in 1942 to describe any substance produced by a microorganism that is <a href="http://en.wiktionary.org/wiki/antagonism" class="extiw" title="wikt:antagonism" >antagonistic</a> to the growth of other microorganisms in high dilution.<sup id="cite_ref-Wakeman1947_2-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Antibiotic#cite_note-Wakeman1947-2" >[3]</a></sup> This definition excluded substances that kill bacteria, but are not produced by microorganisms (such as <a href="http://en.wikipedia.org/wiki/Gastric_juices" title="Gastric juices" class="mw-redirect" >gastric juices</a> and <a href="http://en.wikipedia.org/wiki/Hydrogen_peroxide" title="Hydrogen peroxide" >hydrogen peroxide</a>). It also excluded<a href="http://en.wikipedia.org/wiki/Chemical_synthesis" title="Chemical synthesis" >synthetic</a> antibacterial compounds such as the <a href="http://en.wikipedia.org/wiki/Sulfonamide_(medicine)" title="Sulfonamide (medicine)" >sulfonamides</a>. Many antibacterial compounds are relatively <a href="http://en.wikipedia.org/wiki/Small_molecule" title="Small molecule" >small molecules</a> with a <a href="http://en.wikipedia.org/wiki/Molecular_weight" title="Molecular weight" class="mw-redirect" >molecular weight</a> of less than 2000 <a href="http://en.wikipedia.org/wiki/Atomic_mass_unit" title="Atomic mass unit" >atomic mass units</a>.</p>
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With advances in <a href="http://en.wikipedia.org/wiki/Medicinal_chemistry" title="Medicinal chemistry" >medicinal chemistry</a>, most of today's antibacterials chemically are <a href="http://en.wikipedia.org/wiki/Semisynthetic" title="Semisynthetic" class="mw-redirect" >semisynthetic</a> modifications of various natural compounds.<sup id="cite_ref-3" class="reference" ><a href="http://en.wikipedia.org/wiki/Antibiotic#cite_note-3" >[4]</a></sup> These include, for example, the<a href="http://en.wikipedia.org/wiki/Beta-lactam_antibiotic" title="Beta-lactam antibiotic" >beta-lactam</a> antibacterials, which include the <a href="http://en.wikipedia.org/wiki/Penicillin" title="Penicillin" >penicillins</a> (produced by fungi in the genus <i><a href="http://en.wikipedia.org/wiki/Penicillium" title="Penicillium" >Penicillium</a></i>), the <a href="http://en.wikipedia.org/wiki/Cephalosporin" title="Cephalosporin" >cephalosporins</a>, and the <a href="http://en.wikipedia.org/wiki/Carbapenem" title="Carbapenem" >carbapenems</a>. Compounds that are still isolated from living organisms are the <a href="http://en.wikipedia.org/wiki/Aminoglycoside" title="Aminoglycoside" >aminoglycosides</a>, whereas other antibacterials—for example, the <a href="http://en.wikipedia.org/wiki/Sulfonamides" title="Sulfonamides" class="mw-redirect" >sulfonamides</a>, the <a href="http://en.wikipedia.org/wiki/Quinolone" title="Quinolone" >quinolones</a>, and the <a href="http://en.wikipedia.org/wiki/Oxazolidinone" title="Oxazolidinone" class="mw-redirect" >oxazolidinones</a>—are produced solely by chemical synthesis. In accordance with this, many antibacterial compounds are classified on the basis of chemical/<a href="http://en.wikipedia.org/wiki/Biosynthesis" title="Biosynthesis" >biosynthetic</a> origin into natural, semisynthetic, and synthetic. Another classification system is based on biological activity; in this classification, antibacterials are divided into two broad groups according to their biological effect on microorganisms: <a href="http://en.wikipedia.org/wiki/Bactericide" title="Bactericide" >bactericidal</a> agents kill bacteria, and <a href="http://en.wikipedia.org/wiki/Bacteriostatic_agent" title="Bacteriostatic agent" >bacteriostatic agents</a> slow down or stall bacterial growth.</p>