28 March 2009

the rise of super bugs

Three years ago I wrote my undergraduate dissertation on horizontal gene transfer, transposons and antibiotic resistance in bacteria. Whilst that was written from a genetic point of view, this post aims to explore the environmental stresses that contribute to the rise of antibiotic resistances. There are several reasons for this and the most important ones:
  • medical abuse of antibiotics
  • usage of antibiotics in animal feed
  • genetically modified crops
  • usage of antibiotics in personal and household cleaning products
  • mutations occurring in bacteria
Antibiotic use in hospitals:
One of the major causes for the rise of resistant strains is the careless use of antibiotics by patients and prescribing physicians. Antibiotics should not be prescribed in the case of viral infections. Patients should be told to complete the full course of antibiotics. Medical practitioners should observe basic hygiene measures to prevent the spread of multi-drug resistant strains around the hospital and between patients.

Usage in animal feed:
Antibiotics can be administered to livestock as part of therapy for an animal or group of animals obviously exhibiting clinical signs of the disease or they can be administered as part of control or prevention. Growth promotion is the case in which antimicrobials are added to the feed over a period of time, which results in improved physiological performance. Antibiotic resistance can very quickly percolate through the food chain and through meat and other food products ultimately affecting humans. Animals that carry resistant strains are a direct hazard to those that work with them.

The use of antibiotics in food animals selects for bacteria resistant to antibiotics used in humans and these might spread via the food to humans and cause human infection. By avoiding meat that is grown on farms that most likely use antibiotics, you can protect yourself and the environment. Eat organic, reduce your meat intake - both of which are healthier options.

Genetically Modified Crops:
Antibiotic resistance markers are used in modifying crops in order to track whether the inserted gene is properly taken up by the host. This means that the antibiotic resistant gene is still active in the crop which if consumed can easily interact with gut bacteria to increase antibiotic resistance. Additional interactions with soil bacteria is also very possible. The answer to avoid this is easy - eat organic food and if your government is considering introducing GM food, then use your voice to stop the influx of unsafe food.

Usage of antibiotics in personal and household cleaning products:
Out of all the utterly pointless use of antibiotics, this takes the cake. I'm talking about soaps and kitchen product that are advertised as 'anti-bacterial' -- most of these contain low-grade antibiotics in minute quantities, usually Triclosan. Releasing low-grade antibiotics into the environment only worsens the situation as it gradually builds up antibiotic resistance. Studies have proven that this only temporarily kills bacteria on surfaces and within an hour old bacterial levels are present again. Soap and water still works! It's better for your skin and the environment.

Bacterial Mutations:
Bacteria are organisms which mutate very easily. They do have DNA proof-reading abilities much like our cells but due to short generation spans, mutations arise far more quickly. In addition bacteria also have a system of gene transfer which occurs cell to cell across generations and across species which makes the spread of antibiotic resistant strains extremely easy.

Initially when resistant strains of bacteria were discovered, it was found that they acquired resistance to only to a single antibiotic. As time went by and environmental selection on bacteria increased, they developed the ability to code for different antibiotic resistances on their genome. When this was transferred to other strains, these strains also became resistant to several drugs at the same time with only a single genetic transfer. This poses an incredible advantage to bacteria because it renders them resistant to a vast number of antibiotics. On the other hand, it is a terrible disadvantage to medical science because most antibiotics are ineffective and the use of very powerful antibiotics must be resorted to.

There are some antibiotic resistances which occur due to point mutations and are therefore, not transferable. However, in most cases, antibiotic resistances in bacteria result from the acquisition of a foreign resistance gene. As bacteria multiply and adapt rapidly, the threat of new antibiotic resistant strains looms even greater. This is especially relevant where there is increasing environmental pressure for bacteria to adapt. To avoid the occurrence of antibiotic resistance and outbreaks of resistant strains, prudent use of the available antibiotics is necessary. The use of antibiotics in the food and agriculture industry also contributes to resistant strains.

Just sixty years ago people died of very minor infections that can be cured today with an of antibiotics. Even today there are people in parts of the world with limited access to antibiotics to treat severe infections and there are some others who abuse it by adding it to hand-wash. Since the discovery of penicillin, bacteria have adapted to the onslaught of antibiotics and will only continue to do so. They are equipped with mechanisms of survival that we are only beginning to comprehend. It is the prudent use of existing, as well as any new antibiotics that might be discovered, that will ultimately alleviate the situation.

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