Antibiotic resistance: even more interesting and scary than before

example of selection for bacteria by antibioti...

In vitro selection of antibiotic resistance to ampicillin: Image via Wikipedia

I came across a fascinating primary research article from the journal Nature, via the science blog  The research details the examination of DNA recovered from ancient soil microorganisms in Siberian permafrost, and has been rigorously dated to approximately 30,000 years before the present. The analysis is what is called metagenomic, and gives an indication of the DNA of all of the different species of organisms present within a population. It would be analogous to a scientist taking all of the animals in a zoo together, and recovering the DNA to make conclusions about the zoo: you would be able to see all of the DNA present in that group, but you would not have a way to determine whether a specific gene was associated with a lion for instance. That is a drawback to the methodology, but it does enable you to study organisms which are present in very small numbers, or otherwise cannot be isolated in the laboratory.

The scientists from McMaster University in Ontario, Canada isolated this ancient DNA, and looked for gene sequences that they recognized. Among the familiar genes were sequences that encoded antibiotic resistance proteins from bacteria found in medical settings today. From the abstract:

Here we report targeted metagenomic analyses of rigorously authenticated ancient DNA from 30,000-year-old Beringian permafrost sediments and the identification of a highly diverse collection of genes encoding resistance to β-lactam, tetracycline and glycopeptide antibiotics. Structure and function studies on the complete vancomycin resistance element VanA confirmed its similarity to modern variants. These results show conclusively that antibiotic resistance is a natural phenomenon that predates the modern selective pressure of clinical antibiotic use.

Antibiotics were introduced for therapeutic use, beginning with the identification of penicillin by Alexander Fleming in 1928, and continues to be the topic of extremely active research in the present day. However, despite the very clear benefit of these compounds in modern medicine, their continued use has significant drawbacks. Many common infections are becoming increasingly difficult to treat today in comparison even to a decade or two ago, due to the acquisition of antibiotic resistance by many patient isolates. What was easily treatable a generation ago now can lead to an extended hospital stay or death today, and represents a looming health care crisis for the us in the very near future.

Microorganisms become resistant to antibiotics via a number of diverse mechanisms, but in the end antibiotic resistance in a single bacterium occurs because that bacterium has a specific DNA sequence that allows it to shrug off the effects of the antibiotic and survive in its presence. Spread of resistance to a given antibiotic then occurs as more and more bacteria become exposed to that compound, until most of the population is resistant to its effects. In the clinical setting, it is critical to determine the pattern of antibiotic resistance of any given patient isolate, so that the patient can be given the most appropriate therapy for their condition. It is the job of the microbiologist to determine this, and give that recommendation for treatment to the nurse and physician.

So what is so important about finding the genes for antibiotic resistance in microorganisms from 30,000 years ago? It means that in essence that these microorganisms possessed the ability to withstand antibiotics such as penicillin and vancomycin long before these compounds were introduced for therapeutic use, and implies the possibility that any future antibiotic (one we haven’t discovered yet) may only have limited efficacy as well!

What is our recourse in health care? We need to limit the use of any given antibiotic for only the most appropriate conditions, we need to limit the amount of antibiotics to levels that are effective, and we need to continue to search for novel compounds in a potentially futile effort to stay ahead of the microorganisms. We’ll leave the last of those for the bench scientists to help us out with, but for the first two, it will be the job of every health care worker (physicians, nurses, and technicians) to ensure that we can continue to treat infectious diseases with our existing arsenal of drugs for the near future.


About ycpmicro

My name is David Singleton, and I am an Associate Professor of Microbiology at York College of Pennsylvania. My main course is BIO230, a course taken by allied-health students at YCP. Views on this site are my own.

Posted on September 2, 2011, in Danger danger danger!, Microbes in the News, Strange but True and tagged , . Bookmark the permalink. Comments Off on Antibiotic resistance: even more interesting and scary than before.

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