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Gene: a region of DNA that instructs the cell on how to build protein(s). As a human, you usually get a set of instructions from your mom and another set from your dad... more
Horizontal gene transfer: the process by which bacteria exchange genes with one another without multiplying....more
Mutation: a change in the lineup of DNA instructions. Sometimes, if the DNA changes, then the instructions for what to build will change, or mutate.
Some bacteria are naturally equipped with defenses against antibiotics. One defense that some bacteria have is a chemical that destroys the antibiotic molecule. When the antibiotic is near the bacteria, they release their chemical defense, which causes the antibiotic to stop working. Another way they defend themselves is by changing some of their own proteins so that the antibiotic cannot touch the outside of their cell bodies. For instance, many antibiotics try to latch onto a bacteria’s receptors, molecules that sit on the outside of bacteria and receive signals. Some of these bacteria can change the shape of their receptors, so that the antibiotic can’t bind to it. If it can’t bind, it can’t kill it.
There is a very common antibiotic-resistant bacteria species called Clostridium difficile that causes people to have bad diarrhea. C. diff uses both chemical and shape-changing defenses, and tends to thrive in people who are taking antibiotics for other bacteria.
Sometimes, when a bacterium is multiplying, a random mistake in the bacterium’s DNA will create a gene that gives it resistance to antibiotics. Every time a multiplication event happens, there is a chance a mutation can occur. Because bacteria multiply A LOT, there is a higher chance a mutation like this will occur.
One bacteria species in which this happened is Vancomycin-resistant Enterococci (VRE), a strain of bacteria that is resistant to an antibiotic called vancomycin. VRE have been around for over thirty years, and they are very well studied. In fact, scientists have been able to group different strains of VRE according to how they defend themselves against vancomycin. For two types, called VanA and VanB, the bacteria gained resistance when a mutation occurred in their DNA. This mutation gave the bacteria an ability to fend off the vancomycin molecule.
Some bacteria acquire resistance when they are “given” a gene by another bacterium through a process called horizontal gene transfer (HGT). There are three ways that HGT can occur.
The genes that a bacterium gains through HGT are not always ‘resistance’ genes, but when they are, it greatly increases the risk of antibiotic-resistant bacteria spreading throughout our population.
A dangerous, but also very widespread, bacteria called Carbapenem-resistant Enterobacteriaceae (CRE) is known for its ability to spread ‘resistance’ genes through HGT. CRE can cause infections in our bloodstream, wounds, and urinary tract, and are one of the hardest bacteria to kill, because they can survive almost all antibiotics.
Tyler Quigley. (2017, July 10). Antibiotic Resistance. ASU - Ask A Biologist. Retrieved January 19, 2020 from https://askabiologist.asu.edu/fr/node/3750
Tyler Quigley. "Antibiotic Resistance". ASU - Ask A Biologist. 10 July, 2017. https://askabiologist.asu.edu/fr/node/3750
Tyler Quigley. "Antibiotic Resistance". ASU - Ask A Biologist. 10 Jul 2017. ASU - Ask A Biologist, Web. 19 Jan 2020. https://askabiologist.asu.edu/fr/node/3750
Some bacteria form pili, hair-like appendages shown in a bundle here, that enable them to do well in certain parts of the body of their hosts, or to trade genes with other bacteria.