Sunday, March 4, 2012

Antibiotic Resistance in the Wild

Galapagos Land Iguana- Wikimedia
Our current agricultural methods include giving antibiotics to cattle, a practice that has created a source of antibiotic resistant bacteria that they can pass back to us.  Animals living in close proximity to humans have been shown to carry some of our bacteria in their guts.   Just how close they have to be to us has been a matter of debate and two new papers look at the problem.

A new study reported in went to the heartland of evolution theory, the Galapagos Islands.  No one is allowed to stay on most of the islands, and contact with the animals is strictly controlled, although some islands are more frequently visited than others.

This study showed that "land and marine iguanas and giant tortoises living close to human settlement or tourist sites in the Galapagos Islands were more likely to harbor antibiotic-resistant bacteria than those living in more remote or protected sites on the islands."  Though not the only study to show that wild animals can pick up antibiotic-resistant organisms from tourists and human contact in the wild, it is dramatic when found in such a "pristine" setting.

from Wikimedia
In Are the bugs in wild animals resistant to antibiotics? reported in the, Norwegian researchers went a step further, studying polar bears on the Arctic archipelago of Svalbard.  These animals not only had no human contact but neither did their food sources.  Since some antibiotic chemicals are derived from nature we might expect some evidence of antibiotic resistance in the wild.

The problem is how to get stool specimens from wild polar bears.  Following them across the ice while waiting for the big event is both time consuming and potentially dangerous.  The researcher's answer doesn't seem much less dangerous.  They flew around over the ice in a helicopter and then shot the bear with a tranquilizer gun.  Then they landed and obtained the stool sample with a digital rectal exam.  (Being highly intelligent scientists, I suspect this is where the graduate student came in.)

They tested for blaTEM genes, which are known to encode resistance to a commonly used class of antibiotics that includes penicillins and cephalosporins.  They found only 4 different strains carrying the genes, compared to 13 in domestic cattle and 40 in humans.  They concluded that there are some antibiotic-resistant organisms in nature but they are relatively uncommon.  And I suspect that a graduate student concluded that switching to investment banking would be a good career move.

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