Antibiotics Inhibit Plant Growth

A common antibiotic can be found in wastewater and reduces the ability of plant leaves to capture sunlight.

THE GIST:

- A common antibiotic slows photosynthesis and stunts the growth of plants in lab experiments.

- The finding raises concern that antibiotics could have negative effects on the environment if released in large enough quantities.

- The levels used in the experiments are higher than is typically found in the environment.

A common antibiotic stunts the growth of plants by slowing their ability to convert the sun's light into useful energy for growth, says a new study.

The study raises the question of whether such antibiotics released into the environment through wastewater could affect wild or agricultural plants. Levels found in the environment are generally much lower than those used in the experiment, but in at least one instance, wastewater from near a pharmaceutical production facility had comparable levels.

The study focused on ciprofloxacin, often sold under the name Cipro. It is part of a group of antibiotics called fluoroquinolones that kill bacteria by interfering with bacterial DNA.

Other research had previously shown that fluoroquinolones inhibit the growth of aquatic algae. The new study, published in Environmental Science and Technology, aimed to uncover the mechanism behind the effect of these antibiotics on plants.

Ludmilla Aristilide, now a postdoctoral researcher at Princeton University in Princeton, NJ, used a combination of computer modeling and experiments to determine how ciprofloxacin acts on the plant's >photosynthesis machinery.

"It is inhibiting the ability of chlorophyll molecules in converting the light energy into a useful form," Aristilde said. In Aristilde's experimental studies, spinach plants exposed to high levels of ciprofloxacin over 26 days had markedly fewer, smaller leaves and shorter roots than unexposed plants.

"We know antibiotics are here to stay. They are very important. We just need to know if we need to be concerned about them and to what extent," she said.

The levels used in the experiments are hundreds of times higher than those that affect bacteria, said Joakim Larsson of the University of Gothenburg in Goteborg, Sweden, and much higher than the concentrations that appear to affect algae, so there may be another way that these antibiotics affect algae that occurs at lower ciprofloxacin concentrations.

Larsson tested wastewater from near a ciprofloxacin production facility in Patancheru, India and found ciprofloxacin concentrations comparable to those used in Aristilde's experiments. "At most contaminated sites the levels of fluoroquinolones would be far less," he said.

"And actually, by the river banks in Patancheru, India there are lots of trees growing," he added. "We have demonstrated a strong transport of Cipro via the ground water to nearby water wells...Thus, the roots of these trees are most likely exposed to extraordinary high levels of Cipro. This puts some doubts about how potent Cipro could be for higher plants."

The combined effect of low concentrations of many pharmaceuticals could raise its own concerns, Aristilde added. "If we have mixtures of antibiotics, they may end up in a concentration that may or may not be alarming," she said.

"Wastewater treatment as it exists now is not the most effective against removing pharmaceuticals," she added. "Once we have the tools to do a good risk assessment, we can assess whether we need to spend the extra money to improve our wastewater treatment efficiency. We are still in the infancy of figuring out the actions of pharmaceuticals in the environment."

Whether ciprofloxacin in the environment poses a risk to plants or not, exposing natural bacteria to antibiotics could create a different problem, Larsson noted: "Antibiotic resistance development in bacteria is a real issue of concern as a possible consequence from environmental contamination with fluoroquinolones."

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