Ampicillin resistance is a term that refers to bacterial resistance to the antibiotic ampicillin. Many strains of bacteria are resistant to a variety of antibiotics, however the resistance that is most commonly used in research and industry is ampicillin resistance. It is used as a selectable marker in bacterial transformation. A selectable marker is a feature that allows for the scientist to select only for the bacterial cells that contain the gene that allows the bacterium to be resistant. This selection is done by growing the bacteria on or in a medium that contains ampicillin. All the cells that lack the amp resistance gene will be killed off, leaving only those with resistance.
The need for selectable markers is important when it comes to genetic engineering, or modifying an organism to become more useful to humans. An example for this is using bacteria to produce chemicals, such as insulin. In order for the bacteria to produce insulin, the gene for insulin production needs to be inserted into the cell of the bacteria. This is done by inserting the insulin gene into a vector, or plasmid, and allowing bacterial cells to transformation. Transformation is the act of taking in extracellular DNA. Most bacteria will instantly degrade, or destroy, this extracellular DNA. However, a few cells will accept it and allow it to integrate into their cell, and now that bacterial cell can produce insulin. In order to isolate only the bacteria that can produce insulin, the gene for ampicillin resistance is also spliced in to the same vector that contains the gene for insulin production. After exposing the bacteria to plasmid DNA, they are grown on nutrient agar, or in a nutrient broth, that contains the antibiotic ampicillin. The cells who have successfully taken in the plasmid will survive due to the amp resistance gene, while the cells who did not take up the DNA will die. The scientist can now collect the live cells, who are now amp resistant and can produce insulin, and begin to grow them in very large vats. The bacteria will produce the insulin which can be purified and sent off for human use.
Although ampicillin resistance can be a huge benefit to scientists, it can also cause problems in regards to medical treatment. If this resistance accidentally spreads to other, more harmful bacteria, then those infections become harder to treat. In today's society, more and more bacteria are becoming resistant to antibiotics that used to work on them. When talking about issues in medical treatment, antibiotic resistance cannot be limited to just ampicillin. There are more serious bacteria that are resistant to other types of bacteria. An example is MRSA, or Methicillin-Resistant Staphylococcus aureus, which has become extremely difficult to treat with antibiotics. Methicillin is a much stronger antibiotic than the relatively weak ampicillin, which is why methicillin is not used as a selectable marker in scientific industry or research. If the ampicillin resistance gene accidentally spreads to other bacteria, then there are stronger antibiotics to kill off the bacteria. However, if a strong antibiotic such as methicillin or vancomycin was used as a selectable marker, and the resistance spread, there would be large repercussions.