superbugs and antibiotics

AQA new spec unit 2

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  • Created by: lydia
  • Created on: 05-05-09 17:30

Bacterial cell

prokaryote - no true nucleus

DNA arranged in large circle of DNA (nucleoid) and plasmids NO CHROMOSOMES

Plasmids may give resistance to antibiotics

Cell wall - made of peptidoglycan

May have capsule, flagellum and some have photosynthetic membranes

Bacteria evolve by mutations of DNA (changing quantity of DNA, inversion, deletion, addition, etc)

Changes in DNA may cause changes to gene, causing changes to amino acid sequence and protein 9functional / non functional)

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Conjugation - horizontal gene transfer

1 bacterial cell transfers DNA to another bacterial cell

Bacterial cells joined by sex pilus and replicated plasmids can pass along it from 1 cell to the other

recipient cell acquires new characteristics from donor cell

Bacterial cells do not have to be same species - allows transfter between harmless and pathogenic bacteria - SUPERBUGS!!

Allows bacterial cells to posess multiple plasmids so allowing resistance to many different antibiotics

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vertical gene transmission

Bacteria reproduce asexually

Divide by mitosis

produces 2 identical daughter cells

DNA from parent cell passed to daughter cell and subsequent generations

If parent cell has antibiotic resistance it will be passed on to daughter cells

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Bacteria and antibiotics

Effect bacteria in different ways (prevent protein synthesis, prevent DNA synthesis etc)

May effect cell wall - cell wall allows bacterial cell to take up water by osmosis without bursting (osmotic lysis) - e.g. inhibit cross linkages within cell wall structure. This weakens the cell wall and causes the cell to burst by osmotolysis.

Only effect cell wall when bacterial cell is growing

e.g. penicillin

Some bacteria may become resistant to antibiotics - pump antibiotic out of cell, change target protein for antibiotic within cell, destroy antibiotic when it enters the cell

Resistant forms survive when treated with antibiotic and continue to reproduce - survival of the fittest

Important examples for AQA - Tuberculosis and MRSA

Tuberculosis - long treatment (6 months) so when patients start to feel better they stop taking antibiotic. Not all bacteria have been destroyed - most resistant forms to antibiotic survive. These survive, reproduce - lead to antibiotic resistant strains

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MRSA - Staph aureus strain resistant to 1 or more antibiotics. Found in hospitals as 1. lots of elderly and sick so more vulnerable to infection 2. People close together - transmission by touch 3. lots of different antibiotics being used so strains can develop multiple antibiotic resistance ( antibiotic resistant strains swapping plasmids by conjugation)

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