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03 Penicillin as an Antibiotic
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03 Penicillin as an Antibiotic

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  • 1. Penicillin as an antibiotic• In general, antibiotics bring about their effects in a number of ways: – Inhibiting protein synthesis – Interfering with the synthesis of bacterial cell walls – Interfering with the functioning of the cell membrane – Inhibiting enzyme activity – will disrupt metabolism ALBIO9700/2006JK
  • 2. The mode of action of penicillin• Broad spectrum bacteria• Interferes with synthesis of cell wall – inhibits enzymes involved in the synthesis of cross-links between peptidoglycan polymers in bacterial cell walls• Strains of Mycobacterium tuberculosis are resistant to penicillin because it possesses enzymes that break down penicilllin (penicillinase)• Antibiotics are ineffective against viruses: – Viruses do not have any form of cell structure or metabolism – Replicates only within living host cells – Eukaryotic mechanisms which are not affected by antibiotics – Absence of cell wall means penicillin has no effect on viruses ALBIO9700/2006JK
  • 3. ALBIO9700/2006JK
  • 4. The causes and effects of antibiotic resistance• Natural selection can change the frequency of alleles in the population so that most of the bacteria in the population are resistant, by the following steps: – Within natural populations of bacteria, some individuals have alleles of genes which give resistance to a particular antibiotic – Bacteria cause an infection, leading to treatment of the infected person with antibiotic – The antibiotic will kill susceptible bacteria, but resistant bacteria will survive – Only the resistant bacteria will reproduce – increase in the frequency of the bacteria that are resistant to that particular antibiotic – Increase in allele frequency for the allele of the gene that gives resistance in the population of bacteria – People infected in the future are infected by bacteria more likely to carry the alleles for resistance ALBIO9700/2006JK
  • 5. • Alleles of genes that cause resistance arise fro the first time by mutation• Such genes located on plasmid – can rapidly spread from one bacterial species to another since plasmids are naturally exchanged between species• Bacteria can acquire resistance to a number of antibiotics because plasmids may contain a number of different antibiotic resistance genes• Such populations of bacteria may cause infections that are difficult to treat ALBIO9700/2006JK
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