By slowly starving them of nutrients and/or oxygen through successive generations, they found that in the absence of tetracycline, both microbes dumped the resistance plasmid, though not entirely in the case of E. coli. But P. aeruginosa completely shed the genetic element responsible for resistance, which made it susceptible once again to antibiotics. When a high level of tetracycline was present, both microbes retained a level of resistance.
One long-recognized problem with antibiotics is that they tend to snatch defeat from the jaws of victory. If any antibiotic-resistant bacteria are part of a biological mix, whether in a person, an animal or in the environment, the weak microbes will die and the resistant will survive and propagate; this process is known by biologists as "selective pressure."
So there is incentive to eliminate the resistance plasmid from bacteria in the environment as close to the source as possible. The experiments point to possible remediation strategies, Alvarez said. "There are practical implications to what we did," he said. "If we can put an anaerobic barrier at the point where a lagoon drains into the environment, we will essentially exert selective pressure for the loss of antibiotic-resistant genes and mitigate the propagation of these factors."
An anaerobic barrier may be as cheap and simple as mulch in the drainage channel, he said. "If you have a CAFO draining through a channel, then put an anaerobic barrier in that channel. A mulch barrier will do." He said a mulch barrier only a meter thick could contact slow-moving groundwater for more than a month. "That may not kill the bacteria, but it's enough to have bacteria notice a deficiency in their ability to obtain energy from the environment and feel the stress to dump resistant genes."
Alvarez has been chipping away at the problem since moving to Rice from the University of Iowa in 2004
|Contact: David Ruth|