Monday, September 14, 2015

What is Antibiotic Resistance?

The World Health Organisation (WHO) defines antibiotic resistance as the “resistance of a microorganism to an antimicrobial drug that was originally effective.” According to the Centers for Disease Control and Prevention, antibiotic resistance is “the ability of microbes to resist the effects of drugs – that is, the germs are not killed, and their growth is not stopped,” adding that infections “with resistant organisms are difficult to treat, requiring costly and sometimes toxic alternatives.” Antibiotic resistance, which is specific to bacteria, is part of a broader phenomenon known as antimicrobial resistance. This includes bacteria, parasites, viruses and even fungi.

How is it caused?

Antibiotic resistance is part of a natural process that might best be thought of in terms of selection. In the presence of antibiotics (i.e. when an infected person or animal is put on a course of antibiotics), conditions will inevitably favour those organisms that are able to frustrate, counteract, or inhibit the effective operation of the drug. This can happen in various ways, although two of most common involve either the strengthening or addition of the bacterial protective membrane, or a process known as efflux, whereby the chemicals introduced into the organism are flushed out before they can be effective. Traits such as an additional protective membrane or enhance efflux can occur as part of so-called “erroneous replication” – in effect a process of mutation.

How does it spread?

The most important way in which antibiotic resistance spreads is through the process of replication. All replicates of a resistant bacterium are likely to inherit the trait that is the source of the resistance. This means that in a host environment where antibiotics are present, conditions will favour resistant bacteria and their replicates. Treatment in a situation like this is not only likely to be more expensive, but it will also generally take longer. This in turn means that patients will often be infectious for longer, meaning that there is a greater probability that the infection will spread to others.
Another way in which antibiotic resistance spreads was described by Jerry Wright (chemical biologist at McMaster University in Ontario, Canada) in a recent interview with the Guardian: “Bacteria are very promiscuous and the most shocking thing we’ve realised over the past 60 years is just how rapidly this gene sharing occurs. They often acquire these resistance genes in packages, giving them resistance to multiple antibiotics at the same time, and that’s a major problem in hospitals.” These packages – also known as plasmids – enable bacteria to actually trade these resistance traits among themselves, and thereby to spread them rapidly.

How does it affect us?

Widespread misuse of antibiotics, in healthcare and animal husbandry, is largely responsible for the pandemic proportions of this problem, but it is also a very natural consequence of any antibiotic use at all. Predictions as to the future impact of the global spread of antibiotic resistance are dire, with the WHO itself pointing to the possibility of what it calls “the post-antibiotic era,” where “common infections and minor injuries, which have been treatable for decades, can once again kill.” Some have even suggested that simple surgical procedures might be impossible within the next two decades due to the risk of infection. Antibiotic resistance already causes close to a million deaths annually across the globe, and that number is projected to increase tenfold by the middle of the century.

What can be done?

Understanding the scale of the problem is one of the most serious challenges in the struggle against antimicrobial resistance, with the CDC calling for increased surveillance at the state level. In many parts of the world, no such monitoring programs exist at all, which also means that the potential for under-reporting is vast.

Another potent tool would be the development of new antibiotics (antibiotic development has been in decline since the late eighties), or the resurrection of old ones which might be deployed in novel ways and combinations now that scientists better understand the way they work. There have also been sustained calls for better stewardship by healthcare workers, pharmacists and others to ensure that they prescribe antibiotics more selectively and educate patients about the risks involved in not finishing a course, taking prescriptions meant for others, stockpiling antibiotics for later use, etc…
Work is also needed in terms of detection and diagnostic tools. Monitoring of this problem is still very much in its infancy in terms of coordination, efficiency and cooperation at the international level.

Antibiotic Resistance in the Chobe River System

Dr Alexander and her team have established the presence of antibiotic resistant bacteria among wildlife populations in the Chobe region. As part of their ongoing research on this issue, they are now seeking to establish whether or not these resistant bacteria are to be found in the river itself and, if so, how they got there, how widespread they are and what antibiotics, exactly, they have developed resistance against. This is very much in line with the calls described above to improve global surveillance and monitoring of resistant microorganisms, and might indeed take things a step further by monitoring environmental levels of these dangerous pathogens. One of the interesting things about the mechanisms for spreading antibiotic resistance is the fact that the genetic traits that cause it may also have other consequences for the bacteria. These are thought of in terms of evolutionary costs or benefits - in effect, whether they contribute to increased or decreased fitness, whether they help or hinder the organism in its survivability. As bacteria pass on these traits through replication and by swapping plasmids, they also transfer these costs and benefits. This might indeed prove to be one of the "chinks" in their armour, and might prove useful as part of the increasingly unconventional approaches being taken to combat this looming threat in the scientific world, and gaining a better understanding of the way these processes work is therefore of the utmost importance. 

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