bacteria and antibiotics page refs for this section = textbook p218-225

Download Bacteria and antibiotics Page refs for this section = Textbook p218-225

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  • Bacteria and antibioticsPage refs for this section = Textbook p218-225


  • Good ref = Textbook p66 labels, p65 functions of the structures.Unit 2 Handbook (part 3) p22-24.

  • Name the features A to I belowAHCGDIEBF

  • Bacterial DNAOne large circular chromosomeMay also contain a small circle of DNA called a plasmidNot associated with histones (attached proteins)

  • Variation in bacterial DNAOccurs by mutationChange in the organic base sequence in the DNA.Leads to an alteration in the protein produced and changes a characteristic/or a reaction by the bacterial cellThis may allow the bacterial cell to become resistant to an antibiotic.

  • AntibioticsAre ........Substances produced by living organisms that can destroy or inhibit the growth of microorganisms

  • Osmotic lysisThe antibiotic prevents the formation of bacterial cell walls. Water can then enter the cell, causing it to swell and burst. This is osmotic lysis. The bacterium dies.

    Read section on top of HB p23 about MRSA (Methicillin Resistant Staphylococcus aureus)

  • The mutation allows the bacterium to make a new protein enzyme called penicillinase which breaks down the lactam ring structure of the penicillin. This inactivates the penicillin antibiotic. THE RESULT OF A CHANCE DNA MUTATION LEAD TO SOME POPULATIONS OF BACTERIA BECOMING RESISTANT TO THE ANTIBIOTIC PENICILLIN The Structure of Penicillin Antibiotic:


  • Vertical Gene Transmission by Bacterial Cell Division ie Asexual reproduction/binary fission

  • Vertical Transmission

  • Bacterial reproductionBacteria reproduce by a method called binary fission, which is asexual.

    The first stage involves DNA replication. Then the cell splits into 2, so that each new daughter cell produced contains a genetically identical copy of the main circular chromosome and the plasmids.

  • Horizontal Gene Transmission by Bacterial ConjugationSecond bacterium receives a copy of the plasmid from the other bacterium.

  • Conjugation

    A sex pilus forms a temporary link between the donor and recipient bacterial cells.A plasmid with a resistance gene(s) is transferred directly to the recipient cell.Both bacterial cells now contain a copy of the plasmid and will both now be resistant to a certain antibiotic.

  • Conjugation in Bacteria with a PlasmidSpecies ASpecies B

  • 1. In a large enough population of microorganisms a small number are naturally resistant through random genetic variation i.e. via a spontaneous mutation2. Exposure to antibiotic eliminates the susceptible majority.3. The small number of survivors multiply rapidly in the absence of competitionEvolution of Antibiotic Resistance in Bacteria4. The population is now more or less 100% antibiotic-resistant

  • Some bacteria will be resistant to a particular antibiotic Resistant bacteria have a selective advantage in the presence of the antibioticIn the presence of the antibiotic

    Non-resistant bacteria are inhibited or destroyed by the antibioticResistant bacteria flourish in the presence of the antibiotic, because there is little competition for nutrients. (selected population)How does resistance develop in a population of bacteria?There will be variation in the population as a result of:Mutation or Conjugation

  • TASK: Check your missing words task top of HB p24ANSWER WORDS in the correct order for the answers:


  • Development of antibiotic resistance to TB

  • Why is TB so difficult to treat:Treatment for TB involves taking antibiotics for 6-9 months non-stop.As patients start to feel better they tend to stop taking their antibiotics. However, at this point even though the most susceptible TB bacteria have been killed, a few TB bacteria that are more resistant will remain alive in the body.Resistant strains of TB Mycobacterium survive, multiply and can even pass on their alleles for resistance to other strains/species of bacteria by conjugation.

  • Multiple-antibiotic resistant strains of TB have developed.

  • Superbugs!Bacteria which are resistant to one antibiotic may pass the plasmid containing the resistance gene to another bacterium which is already resistant to a second antibiotic.

    This then multiplies leading to resistance to both antibiotics etc.

  • How bacteria can become resistant to more than one antibioticBacteria treated with antibiotic ABacteria treated with antibiotic Bresistant bacteriumresistant bacteriummost bacteria are killedmost bacteria are killedduring conjugation the plasmid with the gene for resistance to antibiotic A is copied into the bacterium already resistant to antibiotic Bbacterium resistant to antibiotics A and Bresistant bacterium multiplies to form a new strain resistant to antibiotics A and B

  • MRSAMRSA (methicillin-resistant Staphylococcus aureus) infections are more difficult to treat due to the antibiotic-resistance of the bacteriaSome strains are resistant to nearly all antibioticsIt causes a range of illnesses from skin infections to life-threatening meningitis or septicaemiaIt can take time to determine which drugs to use to treat it, so patients can become very ill

  • MRSA (cont)People in hospitals tend to be weaker and more vulnerable to infectionCareful attention has to be paid to not transfer infection between patients

  • A few pictures of MRSA sufferers

  • Do the application exercise from p222 NT textbook on

  • If you have a Biology AS revision guide, there is a REALLY EXCELLENT double page spread ON P84-85 to study about the use of antibiotics, the ethical considerations connected with this and antibiotic resistance by bacteria on p84-85. It would be valuable for you to read this!

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