Now, a new paper in the journal Science reveals an uncomfortable prospect: Friendly soil bacteria might be transferring their antibiotic-resistance genes to human pathogens.
It is important to understand that antibiotic-resistance existed long before humans ever came around. Antibiotics are biological weapons; they are produced by one bacterial species to kill other bacterial species. For instance, tetracycline (along with several other important antibiotics) is produced by the genus Streptomyces, which lives in the soil. Natural selection pressured other bacteria to evolve resistance to this assault. Therefore, not only does an arsenal of antibiotic-producing genes exist in nature, so does an entire arsenal of antibiotic-resistance genes.
The researchers grew bacteria from various soil samples. They extracted the DNA and sequenced it, and they discovered multiple genes for antibiotic resistance. Then, they compared these DNA sequences to those of pathogens isolated from human patients. Many of the sequences were nearly identical. Because the soil bacteria and the human pathogens are only distantly related, this strongly implies that the soil bacteria directly transferred their antibiotic-resistance genes to the pathogens (or vice versa) via a process called "horizontal gene transfer."
Regardless of the direction of transfer, this is a serious cause for concern. If soil bacteria transplant their resistance genes to pathogens, it makes pathogens stronger. If pathogens are transferring their genes to soil bacteria, it implies that soil bacteria could someday become pathogenic. (This may be how the bacterium Acinetobacter baumanii -- which is infamous for causing infections in wounded American soldiers from Iraq -- became pathogenic.)
Therefore, the "resistome" -- or the collective antibiotic resistance of an environmental bacterial sample -- may be of far greater clinical significance than previously imagined. It may be wise to heed this warning and take action to severely restrict antibiotics in livestock feed before the enormous problem of antibiotic resistance gets even worse.
Source: Kevin J. Forsberg, Alejandro Reyes, Bin Wang, Elizabeth M. Selleck, Morten O. A. Sommer, Gautam Dantas. "The Shared Antibiotic Resistome of Soil Bacteria and Human Pathogens." Science 31: 337 (6098): 1107-1111. (Aug 2012). DOI: 10.1126/science.1220761
(Photo: Acinetobacter baumanii via Wikimedia Commons)