Testing Antibotics On Bacteria Essay Research Paper — страница 2

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strains of the bacteria Escherichia coli can cause food poisoning in young children, the elderly, and people with impaired immune systems. E. coli 0157: H7, normally found in the intestines and fecal matter of humans and animals, can survive in meat if the meat is not cooked past 155 degrees F. A 1993 U.S. outbreak of this type of food poisoning, which affected over 450 people, was attributed to contaminated hamburgers that were cooked rare. In 1928, Alexander Fleming noticed that growth of the pus-producing bacteria, Staphylococcus aureus, had stopped around an area in which an airborne mold contaminant, Penicillium notatum, had begun to grow. Fleming determined that a chemical substance had diffused from the mold, and named it penicillin. The small, impure amounts he initially

extracted lacked potency, yielding disappointing results in early attempts to treat human infections with penicillin. In 1939, Ernst Boris Chain, Howard Walter Florey, and Edward Penley Abraham at Oxford University began to study the possibility that purer, more stable penicillin preparations might be effective. In 1941 the partially purified material was administered to a policeman suffering from osteomyelitis. Dramatic improvement ensued, but the supply was exhausted before a cure could be effected, and the patient died. Nonetheless, the matter obviously deserved further exploration, and the outbreak of World War II added an element of urgency. The war, however, interfered with attempts to make penicillin in England on a large scale. Chain therefore hand-carried a vial of the

mold to the United States, where the necessary industrial capacity was available for mass production. Application of beer-brewing technology yielded large amounts of mold liquor, from which partially purified penicillin could be laboriously recovered for clinical use. The first batches became available for military use in 1943. The material was so scarce that patients’ urine was collected and the excreted penicillin recrystallized to be used again. Meanwhile, Rene Dubos at the Rockefeller Institute had been pursuing Pasteur’s original train of thought. Observing that microbial populations in soil held one another in check, he isolated and purified an antibiotic from a soil bacterium in 1939. It and similar substances subsequently isolated were effective when applied to

superficial wounds but proved too toxic for systemic administration. By 1944, Selman Abraham Waksman and his colleagues had isolated streptomycin from a soil microbe and proved its effectiveness against the tubercle bacillus. Between 1945 and 1960, a systematic search was carried on for antibiotics derived from bacteria and molds found all over the world. Many hundreds of antibiotics were discovered, and dozens were screened for antibiotic activity and toxicity. Many were eventually marketed, and prescription use accounted for hundreds of tons annually. In 1957, penicillin was synthesized in the laboratory. Complete synthesis of penicillins proved prohibitively expensive, but harvesting the basic molecules of penicillin from Penicillium molds and then tacking on diverse molecules

proved feasible and led to a large number of tailor-made penicillin variants. The 1960s witnessed a veritable explosion of so-called semisynthetic (part mold-made, part synthetic) penicillins, each designed to deal with the increasing problem of penicillin-resistant bacteria, to achieve better absorption and higher concentrations in the body, or to broaden the penicillins’ effective antimicrobial spectrum. Conclusion My conclusion is that my hypothesis was only partially correct. In my hypothesis I stated that penicillin would inhibit bacterial growth best in Bacillus subtilis. This section of the hypothesis was correct. However, I also stated that tetracycline would inhibit bacterial growth best in Escherichia coli. This section was incorrect. The antibiotic that worked the

best on Escherichia coli was nalidixic acid. Results In my experiment I received the following results: Bacillus subtilis (gram positive) Growth Area: Tetracycline:12 mm Novobiocin:9 mm Chloramphenicol:18 mm Strepomycin:11 mm Penicillin:21 mm Erythromycin:15 mm Escherichia coli (gram negative) Growth Area: Chloramphenicol:17 mm Kanamycin:11 mm Triple sulfa:9 mm Nalidixic acid:17 mm Furadantin:14 mm Table 1 Escherichia coli Bacillus subtilis Antibiotic Width in mm Antibiotic Width in mm Chloramphenicol 12 Tetracycline 12 Kanamycin 11 Novobiocin 9 Triple sulfa 9 Chloramphenicol 18 Nalidixic acid 17 Strepomycin 11 Furadantin 14 Penicillin 21 Tetracycline 10 Erythromycin 15 Bibliography United States Pharmacopeia. Complete Drug Reference.Consumer Reports Books, Yonkers, New York.