Researchers from
North Carolina State University have found a gene that gives Salmonella
resistance to antibiotics of last resort in a sample taken from a human patient
in the U.S. The find is the first evidence that the gene mcr-3.1 has made its
way into the U.S. from Asia.
There
are more than 2,500 known serotypes of Salmonella.
In
the U.S., Salmonella enterica
4,[5],12:i:- ST34 is responsible for a significant percentage of human
illnesses. The drug resistance gene in question -- known as mcr-3.1 -- gives
Salmonella resistance to colistin, the drug of last resort for treating
infections caused by multidrug-resistant Salmonella.
"Public
health officials have known about this gene for some time," says
Siddhartha Thakur, professor and director of global health at NC State and corresponding
author of the research. "In 2015, they saw that mcr-3.1 had moved from a
chromosome to a plasmid in China, which paves the way for the gene to be
transmitted between organisms. For example, E. coli and Salmonella are in the
same family, so once the gene is on a plasmid, that plasmid could move between
the bacteria and they could transmit this gene to each other. Once mcr-3.1
jumped to the plasmid, it spread to 30 different countries, although not -- as
far as we knew -- to the U.S."
Thakur's
lab is one of several nationally participating in epidemiological surveillance
for resistant strains of Salmonella. The lab generates whole genome sequences
from Salmonella samples every year as part of routine monitoring for the
presence of antimicrobial-resistant bacteria. When veterinary medicine student
Valerie Nelson and Ph.D. student Daniel Monte did genome sequencing on 100
clinical human stool samples taken from the southeastern U.S. between 2014 and
2016, they discovered that one sample contained the resistant mcr-3.1 gene. The
sample came from a person who had traveled to China two weeks prior to becoming
ill with a Salmonella infection.
See:
Posted by Dr. Tim Sandle, Pharmaceutical Microbiology
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