Antibiotic Resistant Salmonella of Last Resort Found in the United States

Researchers at North Carolina State University have discovered a gene that confers Salmonella antibiotic resistance as a last resort on a sample taken from a human patient in the United States. This discovery is the first evidence that the mcr-3.1 gene was introduced to the United States from Asia.

There are more than 2500 known serotypes of Salmonella. In the United States, Salmonella enterica 4,[5], 12: i: – The ST34 is responsible for a significant percentage of diseases in humans. The drug resistance gene in question, called mcr-3.1, gives Salmonella resistance to colistin, a drug of last resort for the treatment of infections caused by multidrug-resistant Salmonella.

"Public health officials are aware of the existence of this gene for some time," said Siddhartha Thakur, professor and director of global health in the state of NC and corresponding author of the research. "In 2015, they found that mcr-3.1 had passed from a chromosome to a plasmid in China, which paves the way for gene transmission between organisms.For example, E. coli and Salmonella are part of the same family, the gene is on a plasmid, this plasmid could move between the bacteria and they could transmit this gene.When mcr-3.1 jumped on the plasmid, it spread to 30 different countries, but not – to our knowledge – the United States "

The Thakur laboratory is one of many countries involved in the epidemiological surveillance of resistant strains of Salmonella. The laboratory generates annual complete genome sequences from Salmonella samples as part of routine surveillance for the presence of antimicrobial resistant bacteria. When Valérie Nelson, veterinary student, and Ph.D. student Daniel Monte sequenced the genome of 100 clinical stool specimens collected in the southeastern United States between 2014 and 2016 and discovered that one sample contained the mcr-3.1 resistant gene. The sample came from a person who had traveled to China two weeks before getting a Salmonella infection.

"This project has proven the importance of continuous sequencing and monitoring," said Nelson. "The initial project did not concern this gene at all."

"The positive sample dating from 2014, this discovery therefore has implications for the spread of colistin-resistant Salmonella in the United States," said Thakur. "Our lab will continue to try to fill these gaps in knowledge."

The search appears in the Journal of Medical Microbiology and was supported by the National Institutes of Health / Food and Drug Administration (Assignment Number 5U 18FD006194-02). Monte and Nelson are the first author and co-author respectively. Previously, he had been Associate Director of the Emerging Infectious Diseases Program at the Institute of Comparative Medicine in the state of North Carolina.