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Time to Reassess Spraying Antibiotics On Orange Trees

The issue of antibiotic resistance, that is, of antibiotics no longer working for bacterial infections in humans is a huge concern. So why are we squandering the antibiotic oxytetracycline on orange trees sickened with the disease citrus greening when a recent study by University of Florida researchers says it doesn't work?

The US Environmental Protection Agency gave permission for large-scale agricultural use of 2 antibiotics (streptomycin and oxytetracycline) to try to combat the bacterial infection that is destroying vast numbers of orange trees in Florida, Texas, and other states. However, the 2 antibiotics are also used to treat a number of bacterial infections in humans. And the latest development is that a study found that when oxytetracycline was sprayed on citrus trees for 6 months according to manufacturer's directions, it was no more effective than spraying water against the harmful bacteria (Candidatus Liberibacter asiaticus). 

Public health advocates, the FDA (Food and Drug Administration), and the CDC (Centers for Disease Control and Prevention) were all opposed to the EPA's antibiotic approvals for the citrus tree disease. They are very concerned that such large scale use could result in the development of antibiotic resistant bacteria, thus making these antibiotics useless in treating human illnesses. The CDC states that each year in the U.S., at least 2 million people get an antibiotic-resistant infection, and at least 23,000 people die.

Keep in mind that the European Union has banned the agricultural use of both oxytetracycline and streptomycin. Brazil has also banned these 2 antibiotics for agricultural use, and there citrus growers are battling the same citrus greening bacteria in citrus groves.

Steven Roach, a senior analyst for the advocacy group Keep Antibiotics Working has said:  “To allow such a massive increase of these drugs in agriculture is a recipe for disaster. It’s putting the needs of the citrus industry ahead of human health.”

From the NY Times: Spraying Antibiotics to Fight Citrus Scourge Doesn’t Help, Study Finds  

When the Environmental Protection Agency approved the spraying of certain antibiotics three years ago to fight a deadly bacterial infection decimating Florida’s orange groves, growers thought they might have found a silver bullet. But public health advocates reacted with alarm, warning that the large-scale use of medically important drugs in agriculture could help fuel antibiotic resistance in humans.

Now a new study by citrus researchers at the University of Florida suggests the spraying of one of the recommended drugs could be for naught.

The study, published last week in the journal Phytopathology, found that spraying the drug oxytetracycline on trees had no detectable impact on the bacterial disease known as citrus greening that slowly kills orange and grapefruit trees. Citrus greening has led to a 70 percent drop in citrus production across Florida since the pathogen first arrived from Asia in 2005.

Nian Wang, a microbiologist at the University of Florida’s Citrus Research and Education Center and a lead author of the paper, said researchers sprayed the leaves of infected orange trees with the oxytetracycline over a six-month period at concentrations recommended by the drug’s manufacturer but found no difference in the progression of the disease compared to trees that were sprayed with just water.

That’s not to say the drug is completely useless in the fight against citrus greening, which is spread by a pinhead-sized insect called the Asian citrus psyllid. Researchers carried out a parallel experiment by injecting the drug into the trees’ trunks, instead of spraying, and they found a notable decline in citrus greening bacteria.

There’s only one problem: Injecting oxytetracycline into citrus trees is not approved by the E.P.A., and applying the drug via injection would be prohibitively expensive, growers and industry officials say. Another potential nit: Researchers found antibiotic residues in fruit that were more than three times higher than are permissible, a potential hurdle for injecting antibiotics into citrus trees.

But environmentalists and public health advocates said the results suggested that the E.P.A.’s approval of oxytetracycline was based on flawed data, which was provided by Agrosource.

Asked to comment on the study, the E.P.A. did not provide a response.

The drug is one of two human-grade antibiotics that the agency has approved to treat citrus greening, which now threatens commercial groves in California and other citrus-growing states. In humans, the drugs, oxytetracycline and streptomycin, are used to treat pneumonia, syphilis and a broad array of infections. In 2016, the compounds were approved for emergency use on citrus trees in Florida, and in December, the agency expanded the use of oxytetracycline for orange groves across the country. A wider rollout for streptomycin is still pending.

The approvals were made over objections from the Food and Drug Administration and the Centers for Disease Control and Prevention, which said expanded use of the drugs could encourage dangerous bacteria to mutate to survive the drugs and infect humans with pathogens that are impervious to existing antibiotics.

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