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Introduction Antibiotics are chemical compounds that selectively effect the growth of microorganisms. Antibiotics usually do not damage the host cell. Each bacterium has a different level of antibiotic that will either inhibit its growth or kill it. The minimum inhibitory concentration is defined as the lowest concentration of antimicrobial that will inhibit the visible growth of a microorganism after an overnight incubation. Related to this is the minimum bactericidal concentration, which is the lowest concentration of antimicrobial that will prevent the growth of an organism after subculture on to antibiotic free media.MICs are considered the `gold standard’ fordetermining the susceptibility of organisms to antimicrobials and are therefore used tojudge the performance of all other methods of susceptibility testing. However, most often they are used as a research tool to determine the in-vitro activity of new antimicrobials. The MIC is defined as the lowest concentration of a drug that will inhibit the visible growth of an organism after overnight incubation. This period is extended for organisms such asanaerobes, which require prolonged incubation for growth. According to pharmacologists some antibiotics are bactericidal and some are bacteriostatic. These terms are slightlymisleading since all antibiotics are potentially bactericidal and bacteriostatic at different concentrations. The bactericidal and bacteriostatic terminology originates from whether the antibiotic's mechanism is based on inhibiting cell wall formation ("bactericidal") or inhibiting bacterial metabolism or ribosomal protein synthesis ("bacteriostatic"). If cell wall formation is blocked, the organisms will lyse and perish, nonetheless if metabolism or protein synthesis is blocked, the organisms simply slows down. While this is true to some degree, bactericidal or bacteriostatic effects are dependent on the concentration of the antibiotic as well. A low dose of a bactericidal antibiotic may only inhibit bacterial growth, while a high dose of a bacteriostatic antibiotic will be bactericidal. Additionally, organisms which are not multiplying may not be significantly affected by anti-cell wall antibiotics, in which case anti-ribosomal antibiotics would be more effective. By understanding the concepts in determining antibiotic concentrations compared to the MIC and MBC, we can make rational decisions in determining how successful antibiotic treatment is likely to be.