Stewardship / Resistance Scan for Mar 13, 2019

Antibiotics for citrus trees
Origins of MCR-1 in France

EPA urged to deny proposal for more antibiotic spraying on citrus fields

Representatives from the Center for Biological Diversity, Public Interest Network, and US PIRG (Public Interest Research Group) today delivered 45,000 petition signatures to the Environmental Protection Agency (EPA), calling on the agency to deny a proposal that would allow for expanded antibiotic spraying on citrus fields.

Under the proposal, citrus growers would be allowed to spray more than 650,000 pounds of streptomycin on citrus fields to treat the bacteria that causes citrus greening disease. The groups say spraying streptomycin on citrus fields does not cure the disease and would be an irresponsible use of an antibiotic that's considered critically important for human health by the World Health Organization (WHO).

"The more you use antibiotics, the greater the risk that bacteria resistant to the drugs will flourish and spread," Matt Wellington, director of US PIRG's antibiotics program, said in a press release. "The bottom line is that the potential problems created by spraying massive amounts of streptomycin on citrus fields could outweigh the original problem the EPA wants to solve."

The groups say that, if the proposal is allowed, it would be the largest-ever use of a medically important antibiotic in plant agriculture in the United States.

In December, the EPA approved a proposal for wider use of oxytetracycline on citrus trees to combat citrus canker and citrus greening disease.
Mar 13 Center for Biological Diversity press release


MCR-1 in France the result of divergent evolutionary paths, study says

French and Swiss scientists isolated 153 colistin-resistant Escherichia coli strains from fecal samples obtained from 152 patients in Paris and discovered the MCR-1 gene in about 5% of the samples and note that colistin resistance is the result of two distinct evolutionary pathways, according to a study yesterday in the Journal of Antimicrobial Chemotherapy.

The researchers conducted the analysis because they say large epidemiological studies to estimate the human burden of colistin-resistant E coli gut carriage are lacking. They screened 1,217 patients in six Parisian hospitals during a 3-month stretch in 2017. Colistin is considered an antibiotic of last resort for multidrug-resistant infections.

They identified the MCR-1 colistin-resistance gene in 7 (4.6%) of the 153 colistin-resistant E coli samples, and the gene was located on various plasmids, which are mobile units of DNA. Genetic analysis indicated an animal origin for the genes, compared with a human origin for the 146 non-MCR-1 isolates.

The team summarized the findings thus: "We showed that the occurrence at a high rate of colistin resistance in human faecal E. coli is the result of two distinct evolutionary pathways, i.e. the occurrence of chromosomal mutations in an endogenous E. coli population and the rare acquisition of exogenous mcr-1-bearing strains probably of animal origin."
Mar 12 J Antimicrob Chemother study

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