The history of superbugs
Humans have fought infectious diseases for as long as our species has existed. The discovery of penicillin by Alexander Fleming in 1928 finally gave us a major advantage. It helped begin the antibiotic era, during which bacterial infections stopped being the world's leading cause of death. Antibiotics have contributed substantially to longer lives. Everything sounds fine, then – except that microbes found an answer. Nature usually does. This answer is antibiotic resistance, and bacteria that resist several drugs are often called superbugs.
The bacterial nature
To understand how bacteria become resistant to antibiotics, we first need to understand how they live. Microbes are everywhere and are exceptionally successful at colonising places that seem hostile to us. Once bacteria find suitable conditions, many reproduce rapidly.
But reproduction is not their only remarkable ability: bacteria can also acquire and share genes. That ability is central to the emergence and spread of antibiotic resistance.
Genes help define biological traits. In humans they influence features such as eye colour, height and hair colour, and we inherit them from our parents. Bacteria likewise receive genetic information from their ancestors, but they can also gain useful genes from other sources.
Pretty much, yes.
How superbugs evolve
Nature provides several routes by which bacteria can acquire new genes. Four are especially important for understanding how resistance develops and spreads.
1. Bacteria can take up free DNA from their surroundings. When another bacterial cell dies and releases genetic material, a neighbouring cell may incorporate useful genes – including a resistance gene. This process is called transformation.
2. Viruses that infect bacteria can move genes between cells. If a virus accidentally packages bacterial DNA from a previous host, it may inject that DNA into the next bacterium instead of, or alongside, its own genetic material. This process is called transduction.
3. Bacteria can make direct contact through a pilus and transfer genetic material across this bridge. This process, called conjugation, is a particularly important route for spreading antibiotic-resistance genes.
4. Bacteria mutate. Most mutations that arise during replication offer no advantage, and many are harmful. Occasionally, however, a mutation helps a bacterium survive an antibiotic. Under antibiotic selection, that rare variant can multiply and pass the mutation to later generations.
There you have it: several comparatively simple ways in which bacteria can become resistant and contribute to the rise of superbugs.
How we contribute to the rise of superbugs
The situation is serious, but it is not hopeless. Understanding how our use of antibiotics affects bacterial populations is an important part of protecting the drugs that still work.
Consider a familiar example. You feel ill, see a doctor and receive an antibiotic because a bacterial infection is suspected or confirmed. The treatment works and after a few days you feel much better. It may be tempting to change or stop the treatment on your own. The correct course, however, depends on the infection and the prescription, so antibiotics should always be taken exactly as agreed with the treating professional.
First, remember that our bodies contain enormous numbers of bacteria; the vast majority are harmless or beneficial. Second, bacteria reproduce whenever conditions allow, and some species can double within minutes under ideal laboratory conditions.
An antibiotic does not distinguish between a pathogen and every susceptible member of the surrounding microbiome. Treatment therefore changes the whole bacterial community. Susceptible cells are removed, while bacteria that already carry a resistance mechanism are more likely to survive. With less competition, they can multiply. The larger that resistant population becomes, the greater the opportunity for resistance genes to be passed on – potentially even to a future pathogen.
This may sound like science fiction, but genetic exchange and selection occur continuously in microbial communities. Research must continue to develop new treatments, but each of us can help preserve existing antibiotics by using them only when appropriate and following medical guidance. That reduces unnecessary selection pressure and makes it harder for superbugs to gain ground.
