Antibiotics 4.7 Flashcards
What are antibiotics?
Chemicals produced by some bacteria and fungi. Which kill or prevent the growth of bacteria. At low concentrations these chemicals can inhibit the growth of micro-organisms by interfering with their growth and reproduction.
What are bacteriostatic antibiotics?
They prevent bacteria from growing and reproducing.
What are bactericidal antibiotics?
They kill the bacteria directly
What are broad spectrum antibiotics?
They are effective against a wide range of pathogenic bacteria e. g., tetracyclines and affect basic biochemical processes such as protein synthesis.
What is a disadvantage of broad spectrum antibiotics?
It is non-selective and can kill useful microbes that usually compete with pathogenic bacteria and help protect you from infection.
What are narrow spectrum antibiotics?
They are only effective against a limited range of pathogens, e.g., penicillin and affect specific processes in the bacteria, e.g., cell wall formation.
When is a narrow spectrum antibiotic prescribed?
If an infection is not killed by a broad spectrum antibiotic the bacterium needs to be identified and a narrow spectrum antibiotic prescribed. The microbe is cultured and an antibiotic assay carried.
How does penicillin affect bacteria?
- Penicillin is a narrow spectrum antibiotic that inhibits the enzyme glycoprotein peptidase. This enzyme links the peptidoglycan chains that make up murein.
- During the growth of a bacterium holes appear in the cell wall.
- New murein molecules are synthesised to fill the holes and the enzyme glycoprotein peptidase forms the peptide bonds that cross-link the molecules.
- In the presence of penicillin the enzyme is inhibited and the cross-links do not form.
- As the bacterium continues to grow more holes appear in the cell wall - this weakens the cell wall, water enters by osmosis. This causes cell lysis.
What is streptomycin?
It is a broad spectrum antibiotic that inhibits protein synthesis. It does this by blocking the action of bacterial ribosomes thus preventing them from carrying out protein synthesis. Eukaryotic ribosomes have a different structure and are not affected by streptomycin.
How are viruses affected by antibiotics?
They aren’t - they do not have cell walls and don’t carry out biochemical reactions. They also reproduce inside host cells - drugs may not be able to penetrate the host cells and if they did they are likely to damage them.
What causes some bacteria to become resistant to antibiotics?
Random mutations.
How does overuse of antibiotic cause selection for bacteria that are resistant?
1: Antibiotics are widely used to control disease in farming - they are used to reduce the risk of disease spreading through animals kept in confined conditions. This is prophylactic use of antibiotics and has led to the development of resistant bacterial strains.
2: GPs used to prescribe antibiotics readily - over time many bacteria developed resistance to antibiotics.
3: Resistance can be transferred between species of bacteria by transfer of plasmids. This can also happen during sexual reproduction in bacteria.
