B1a4 Infectious Diseases - Antibiotics

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The first antibiotic, penicillin, was discovered by a scientist called Alexander Fleming.  They are medicines that help to cure bacterial (and fungal) diseases by killing infective bacteria inside the body.  Antiobiotics cannot be used to kill viral pathogens which live and reproduce inside cells.  It is difficult to develop drugs which kill viruses without damaging the body's tissues.

In the experiment shown above, an agar plate is spread with a bacterial culture (staphylococcus aureus in this case).  Discs containing antibiotics are then added to the plate.  In the clear areas the bacteria have been unable to grow - they have been killed by the antibiotic diffusing from the disc.  In the bottom right-hand corner, the bacteria can grow around the disc.  They are resistant to this particular antibiotic.

Antibiotic resistance

Antibiotics have revolutionised our treatment of many diseases.  During the First World War many soldiers died from infections that entered wounds.  The Second World War saw the first widespread use of antibiotics and as a result many injured soldiers survived as infections could be treated.  In modern times we have come to depend on antibiotics to treat many bacterial diseases.  However, the overuse of antibiotics has led to the development of resistant strains of bacteria which are no longer killed by a particular antibiotic.  Pharmaceutical companies are trying to produce new antibiotics but recent research has not led to the development of any new antibiotics.  Now resistant strains of bacteria are causing the deaths of many people in hospitals and MRSA (a bacterium resistant to most antibiotics) is becoming more common.

Bacteria (including MRSA) develop resistance to antibiotics as a result of natural selection.  A particular bacterium may mutate spontaneously to produce a resistant strain  The resistant strain can grow and reproduce in the presence of the antibiotic leading to a rise in the population of the resistant bacteria.  In order to reduce the spread of resistant strains of bacteria, antibiotics are not prescribed to treat non-serious infections (e.g. mild sore throats).  Similarly, viruses can mutate to produce new strains.  For example new strains of the flu virus (such as 'swine flu') arise by mutation.  It can spread rapidly through the human population as few people are resistant to the new strain.  If a disease causes mass infections in one country it is called an epidemic.  Mass infections in different countries are called a pandemic.