HOUSTON, March 15 (Xinhua) -- U.S. researchers have "cured" a strain of bacteria of its ability to resist an antibiotic, in a development that has promising implications for a long-standing public health threat, a medical newspaper reported Friday.
Researchers from Rice University in Houston managed to prevent the Pseudomonas aeruginosa bacteria from resisting the antibiotic medication tetracycline by limiting the bacteria's access to food and oxygen, according to the online edition of Texas Medical Center News.
Pedro Alvarez, chair of the civil and environmental engineering department at Rice University, observed the starving bacteria across 120 generations, and found that in every case the starving bacteria chose to conserve energy rather than use its energy to pass on plasmid -- the small genetic element responsible for drug resistance.
Results from this research are the latest in a long effort to understand the environmental causes of antibiotic resistance, which threatens decades of progress in fighting diseases, the report said.
"The propagation of antibiotic resistance has been perceived as a medical -- or microbiology -- related problem," Alvarez said.
"But what many people miss is that it's also an environmental pollution problem. A lot of the antibiotic-resistant bacteria originate in animal agriculture, where there is overuse, misuse and abuse of antibiotics," he said.
Alvarez said confined animal feeding operations are potential sources of environmental contamination by antibiotics and the associated antibiotic-resistant genes that find their way into the ground, water and ultimately the food supply.
"We started with the hypothesis that microbes don't like to carry excess baggage," he said. "That means they will drop genes they're not using because there is a metabolic burden, a high energy cost, to keeping them."
Researchers tested their theory on two strains of bacteria, P. aeruginosa, which is found in soil, and E. coli, which carries resistant genes directly from animals through their feces into the environment.
By slowly starving them of nutrients and/or oxygen through successive generations, the researchers 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. 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, the weak bacteria will die and the resistant will survive and propagate; this process is known by biologists as "selective pressure."
So there's a real benefit to eliminating the resistance plasmid from bacteria in the environment as close to the source as possible, Alvarez said.
"If we can put a no-oxygen barrier at the point where a lagoon drains into the environment, for example, we will exert selective pressure and reduce or eliminate antibiotic-resistant genes at that location," he said.
"That may not kill the bacteria," Alvarez said, "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."