News reports from the past years keep warnign us about the rise of the antibiotic resistant bugs and the potential for a human apocalypse they bring on their microscopic methaphorical shoulders. Their artillery is not visible to the naked eye. Their whole armies aren’t, but can take over a human body and destroy it beyond repair in a matter of days, and some of the most crafty ones – within hours. But there is more you need to know about antibiotic resistant bacteria, and not all of it is bad news!
The biology of resistance
Antimicrobial resistant bacteria are not man-made, but we surely didn’t do much to help our case.
The process by which bacteria become resistant to drugs is (probably) as old as bacteria themselves. Bacteria don’t have sexual reproductive cycles as most animals and plants do. Since they only have one cell, they grow and divide into two cells, which in turn do the same and if food is plenty and the temperature good, these cycles can take place extrmely fast one after the other.
Sharing IS caring between cateria too!
Sexual reproduction was favored throughout evolution because it allows the individuals to exchange genetic material. Each individual carries small variations in their genes which could make it better fit for survival. Exchanging and mixing up these variations brings an extra dose of chance for the new individual to end up with a very favorable set of genes and be even better quipped to prosper in its environment compared to its parents and peers.
Since bacteria don’t have sexual cycles, the variability of their genes is left only to chance – mutations caused by the environment or random mistakes in copying the DNA during the division cycle would be the only way for bacteria to increase the genetic variation of each species. In order to get additional boost, bacteria have evolved a process called conjugation.
Bacteria have one big piece of DNA which stores their whole genome. Some bacteria carry one or few extra smaller pieces of DNA called plasmids. These plasmids can be “donated” from one cell to the other via direct contact. In the end, both cells have the plasmid and the few genes it stores. Antibiotic resistance most often is encoded by the genes in these plasmids.
As bacteria can grow and divide fast, it only takes one cell with a gene for resistance to a drug for the whole population to become resistant in rather short time. As long as there is an antibiotic in the immediate environment of the bacteria, the ownership of resistance gene gives them the only chance to survive. So in essence, the continuous use of antibiotics is the sole human-related reason for bacterial resistance to persist.
How does bacterial resistance affect humans?
The discovery of the antibiotics suddenly increased the human life-span dramatically. Before that, rarely anyone would die of “old age” diseases. People would mostly die from infections – whether a communicable disease or one contracted from a wound or even a small cut.
Less than 90 years after Alexander Fleming discovered antibiotics, and 80- after the first large scale production of antibiotic drugs, we are facing the dreadful possibility to have antibiotics taken away from us, thanks only to our own mismanagement. Over-prescription, misuse and bad production practices allowing leakage in the environment caused the surge of antibiotic resistant bacteria almost immediately after we first started using them to treat diseases. Nowadays, we are starting to lose battle after battle to strains of bacteria causing infections which we used to be able to cure with drugs. Most recently, The World Health Organisation published a report of a drug resistant gonorrhea which can turn into an incurable disease (link to the announcement here).
The biggest cause for the increase of drug resistant bacteria is not the medicinal misuse of antibiotics. It’s farming. By chance, farmers have discovered that antibiotics added to feed boost the growth of many farm animals, even if there’s no infection to be cured at the time. Since then, antibiotics have been widely used as growth promoters. In 2009, the Food and Drug Administration reported that only in the USA, farm animals have been given almost 15 000 tonnes of antibiotics per year. Don’t freak out though! The human exposure to antibiotics via the meat we eat is negligible. First, because antibiotics quickly get inactivated when meat is cooked and also due to practices in food production to reduce the antibiotic content in the final product to a minimum. The problem comes from the amount of antibiotics which “leak” into the environment and increase the “background selection pressure”. In few cases, humans have also contracted resistant infections directly from farm animals (here’s a Center for Disease Control link to explain that).
Antibacterial resistance is costly
It requires extra energy to produce the enzyme, protein, or the anti-toxin for each drug to which this strain is resistant. This often involves maintaining multiple copies of several different types of plasmids. Copying, correcting spontaneous mutations and transferring these copies to the daughter cells when the bacterium divides requires many of the cellular machinery to be engaged in maintaining the resistance trait and diverts nutrients and energy from the growing of the cells. This is another reason why resistant strains grow often slower at first. In turn this only worsens the problem of persistent infections and the spread the resistance – when for example an antibiotic course of treatment is not completed as prescribed the resistant cells would still be alive.
Efforts against the spread of drug resistant bacteria
- Official programs have been started to reduce the amount of antibiotics used as growth promoters as compared to means to treat infections in farm animals.
- Guidance for medical practitioners to avoid prescribing antibiotics unless strictly necessary.
- Pharma companies are continuously developing new types of antibiotics and researchers are constantly experimenting with entirely new types of drugs against bacteria to which resistance develops much slower.
How fast can resistance be overcome?
Because resistance is an expensive trait to possess, it is usually maintained only for as long as it’s necessary – once the antibiotic is not present in the environment (the selective pressure is not in play anymore), the bacteria will lose this plasmid relatively quickly – some as fast as in just few generation times*.
At the same time, researchers are figuring out other ways to overcome resistance. The already mentioned new generations of antibiotics are only one way to go. And probably not the best one, because as long as there is a chemical of any type involved, sooner or later a cell will develop resistance to it and we have to start all over. Antibiotic use management and control is probably one of our best bets against worsening the situation. If we drastically decrease the release of antibiotics in the environment, we will decrease the background selective pressure for bacteria to keep evolving resistance and maintaining it, as sooner than we think many strains might lose their resistance. Yet another, very interesting, method involves the “fight fire with fire” type of action – bacteriophages which would infect bacteria and prevent them from developing resistance (read more on this from this “How Stuff Works” post).
*A generation time for some bacteria can be as sort as 20 minutes!
Think twice before popping the question!
Next time you are feeling under the weather don’t pressure you GP to give you antibiotics unless a test was done and you are both sure it’s bacterial and it will be positively affected by a course of antibiotics.
Talk to your friends and relatives about the problem and make sure they don’t overdo it too (also because antibiotics can have direct negative side effects).
Go ahead and share this post, please. We are at the brink of the Post-antibiotic era, but the outcome might not be entirely to our loss if we act smart!
Do YOU have experience with drug resistant infections?
Share your story in a comment bellow!
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