Mitochondria are bacteria that evolved to live within our cells, so we shouldn’t be too surprised when researchers find that antibiotics affect them:
“After several days of treatment with high doses of doxycycline, mitochondrial respiration was visibly altered,” explains Moullan. More surprising still, the consequences were observed all the way down the food chain, from mammals to flies to nematode worms to plants. “The worms’ development was hindered. On the other hand, signs of aging appeared more slowly, something we had observed in earlier studies.”
The scientists also carried out growth tests on Arabidopsis thaliana, a common plant that’s frequently used in laboratory research. After growing for a week on a normal substrate, it was transplanted into soil with varying concentrations of doxycycline. “Delays in growth, some quite severe, were observed after a few days, even in soils in which the concentration of antibiotics was no stronger than is found in some agricultural soils today,” says Moullan.
This pollution whose consequences are just beginning to be appreciated is caused by the widespread administration of antibiotics to livestock. “Because they are give orally in feed, they are only partially digested and end up in manure, which is then spread on the fields,” explains Mouchiroud.
The quantities involved are huge, and the economic stakes equally sobering. In 2011, 5.6 million kg of tetracycline was administered to US livestock. A study showed that nearly half of the 210 kg of antibiotics produced in China in 2007 were tetracyclines for veterinary use. “The effects on growth of plants other than A. thaliana have not yet been studied, but our work indicates a need for caution,” says Moullan.
The researchers also call on their scientific colleagues to be more careful when using antibiotics in experiments for modulating gene expression. “You observe the effect you’re looking for, but you lose sight of the fact that these substances have serious consequences for overall metabolic function,” says Mouchiroud.