Where Did Superbugs Come From? How Infections Become Resistant to Antibiotics
What Are Superbugs?
Antibiotic drugs are medications that kill or stop the growth of bacteria. Over the past century, a huge variety of antibiotics have been developed to treat the plethora of bacterial species that cause human diseases. But some strains of bacteria have evolved into “superbugs” that cannot be killed easily by antibiotics. The tuberculosis bacteria (Mycobacterium tuberculosis), the “staph” bacteria (Staphylococcus), and other infection-causing bacteria like Enterococcus and Pseudomonas are a few of the species known to have superbug strains.
How Superbugs Evolve
Bacteria reproduce quickly, which means they also evolve quickly. In any population of bacteria, which may contain millions of cells, random mutations may cause one or two individual cells to happen to have a gene that helps protect against an antibiotic. When that population of bacteria is exposed to the antibiotic, these “lucky” cells will be slower to die — or they might not die at all. If they survive to reproduce, their descendants will be resistant to that particular antibiotic drug. They will be slower to die when exposed to that antibiotic in the future, or they may even be completely immune to it.
“Superbugs” are bacteria that are resistant to multiple antibiotics. They are very difficult to kill because the usual antibiotics are useless against them. Superbugs turn back the clock on medicine to the time before antibiotics, when bacterial infections were a constant danger to human life.
What Causes Superbug Evolution?
Every time bacteria are exposed to antibiotics, there is potential for resistance to evolve. The way humans use antibiotics has helped fuel the rise of the superbugs.
The overuse of antibiotics — prescribing them for non-bacterial infections or for mild infections that the immune system could fight off without antibiotics — is a major factor in the evolution of superbugs. Since every exposure of bacteria to these powerful drugs gives them an opportunity to evolve resistance, they should only be used for serious infections.
Another cause is the improper use of antibiotics. Resistance can develop over time, and the first bacteria to experience resistance may be only partially resistant — slower to die than their comrades. If the course of antibiotics is stopped too early, these stronger bacteria will survive. Sometimes, patients taking antibiotics will stop taking them when they feel better instead of completing the full course of the medication, providing an opportunity for resistant bacteria to evolve.
How Superbugs Spread Their Genes
Once the genes for antibiotic resistance evolve, bacteria have ways of spreading them around. Bacteria are asexual, but through a process called transformation or “bacterial sex,” they can trade small segments of DNA.
Sometimes the genes for antibiotic resistance are placed on their own little DNA vehicle, called a plasmid. Plasmids are easily transferred and can carry genes for resistance to multiple strains of antibiotics. Once superbug genes evolve and end up on a plasmid, they can spread to non-resistant bacteria, making those bacteria into superbugs as well.
References
“What Doesn’t Kill Microbes Makes Them Stronger .” Whyfiles. Ed. by Terry Devitt.
