AsianScientist (Mar. 21, 2017) – A team of investigators in China has discovered a new variant on a well-known gene that causes resistance to last resort antibiotics. More troubling, the antibiotic resistance gene was found in a healthy individual during a routine medical examination, suggesting that other healthy carriers may be spreading this resistance unknowingly. These findings were published in Antimicrobial Agents and Chemotherapy.
Polymyxin antibiotics are used as a last resort to treat certain multidrug resistant bacteria. The new mechanism is a variant on the notorious, highly multidrug resistant mcr-1 gene. The investigators have dubbed this new variant mcr-1.6.
“This is the first time an mcr-1 gene has been found in Salmonella in a healthy carrier,” said corresponding author Kan Biao, professor of pathogenic microorganisms and infectious disease control, National Institute for Communicable Disease Control and Prevention, at the Chinese Center for Disease Control and Prevention.
“Healthy carriers play an important role in transmission of resistance genes to the community,” he said.
That’s because they spread disease stealthily, in the manner of the infamous Mary Mallon, who was responsible for several outbreaks of typhoid during the first half of the last century, earning her the sobriquet, Typhoid Mary.
“Salmonella infections have been the leading cause of foodborne illness, and Salmonella-carrying mcr-1 will likely be a problem in food safety,” Kan added.
Mcr-1 and its variants including mcr-1.6 all need to be monitored closely because of their resistance to polymyxin antibiotics, generally, and to colistin, in particular, said Kan. A particular concern is the possibility that new variants on any of these mcr-1 genes could result in increased resistance to colistin. In such cases, higher doses than usual might be necessary when colistin is being used as the last line of antimicrobial treatment following previous treatment failures said Kan.
As with many resistance genes, this one is carried and transmitted on a plasmid, a piece of extra-genomic DNA which can jump from one species of bacterium to another. The particular plasmid carrying this gene, known as IncP, has a broad host range, and a high frequency of jumping from species to species, said Kan—more reasons for careful monitoring.
The article can be found at: Lu et al. (2017) MCR-1.3: A New MCR Variant Carried by an IncP Plasmid in a Colistin-Resistant Salmonella Enterica Serovar Typhimurium Isolated From a Healthy Individual.
Source: American Society for Microbiology; Photo: Shutterstock.
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