You’ve almost certainly heard of “antibiotic resistance”, or “antimicrobial resistance”, or “superbugs”. But do you know what they are? Or why they’re a problem? Or why we’re worrying about them in animals? Read on to find out more!
What is antibiotic resistance?
Antibiotics are a group of medicines that have completely revolutionised medicine (human and veterinary). By selectively killing bacterial, but not mammalian, cells, they allow bacterial infections to be treated.
The first thing to make clear is that antibiotic resistance is a situation where bacteria become resistant to antibiotics. It is not the person, or the animal, that becomes resistant, but the bacteria living inside them. There are many mechanisms bacteria can use to become resistant to antibiotic drugs – sometimes they may develop a pump that removes the drug from inside their cells; sometimes they develop systems that break down the drug before it can work; and sometimes they alter their metabolic pathways so the drug is simply no longer effective.
All of these changes are carried on the bacteria’s genes – the DNA, or blueprint for making that type of bacterial cell – so they are passed on to the next generation as the bacteria multiply and spread.
How does it occur?
Well, it’s important to remember that antibiotic resistance is a perfectly natural phenomenon – it arises from random mutations of the bacterial DNA caused by chance error, solar radiation and naturally occurring chemicals like Radon gas. In fact, bacteria have been retrieved from the arctic permafrost from many thousands of years ago which carry genes for resistance to common antibiotics, millennia before we started using the drugs!
However, back then, the selection pressure on the bacteria was very low (because they were unlikely to come into contact with antibiotics, so the number of bacteria carrying these mutant genes was very low). In the early twentieth century we discovered antibiotics, and (realising almost immediately that they were genuine wonder-drugs) started using them – and over using them. Soon, antibiotics were everywhere, and as we now know, being abused. All of a sudden, bacteria everywhere were being exposed to these drugs – meaning that those with the mutations allowing them to survive in the presence of a particular antibiotic had a massive advantage. The bacteria without those genes died, leaving only the resistant bacteria behind.
Now, initially the doctors (and, later, vets) didn’t worry – there were so few of the resistant bacteria that killing all the others usually resulted in the patient getting better. However, the trouble was that now all the bacteria in that patient were the descendents of the resistant strains – which meant that next time you used that antibiotic, it would be less effective.
To make matters worse, bacteria can be very generous. Although they don’t reproduce in the same way that animals do (they just split in half, forming two new bacteria), they can copy their genes and give the copy to a friend. This is called conjugation, and results in both bacteria having an extra chromosome, called a plasmid. This contains the genes that they’ve borrowed from other bugs, particularly genes for dealing with hostile environments – like antibiotic resistance ones.
Soon, scientists found that bacteria that had never been in a patient that had been treated with antibiotics were expressing genes for resistance – genes that they had borrowed from bacteria who had borrowed them from bacteria who had.
Why is this a problem?
Penicillin (the first “true” antibiotic) started to be used in the mid 1940s, and by the 1950s resistance was already becoming apparent. No one really worried about it, because there were new and “more powerful” drugs coming on the market, so doctors and vets started using those instead. However, the same problem occurred, and nowadays we have multi-drug resistant bacteria, resistant to many, or even all, antibiotics.
Now, antibiotics aren’t just vital for treating bacterial diseases (like pneumonia, for example). They are also essential in many surgical conditions, and without access to effective antibiotics, chemotherapy, organ transplantation and many surgical operations would be either impossible or incredibly dangerous. It wouldn’t be much of an exaggeration to say that without antibiotics, much of modern medicine would be impossible.
As more and more bacteria develop multiple-resistance, antibiotics (in both humans and animals) are becoming less and less effective. Unfortunately, there are very few new types of antibiotic coming onto the market – almost all the new drugs are just chemically tweaked versions of old families, which the bacteria have already learned how to deal with.
It is estimated that by 2050 there will be 10 million human deaths per year due to antibiotic resistance – 10 million people that could be treated now, but we won’t be able to treat in a generation.
Already there are strains of E. coli and Tuberculosis which are resistant to every single antibiotic – and they’re just going to get more common.
Are there any alternatives to antibiotics?
Up to a point, yes. Vaccination against bacterial and viral diseases can reduce the need for antibiotic treatment; and good hygiene can as well. However, at the moment there are no other treatments that can take their place. Although there have been experiments with bacteriophages (viruses that attack bacteria), these have not proven to be clinically useful as yet (mainly because although they work great in the lab, once in the human or animal body their immune system destroys the bacteriophages before they can attack the bacteria).
In Part 2 we’ll look at what actually drives antibiotic resistance in the real world, and what we can all do about it.