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Two mcr resistance genes found in E. coli on commercial poultry farm
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Researchers identified a strain of Escherichia coli carrying two colistin-resistance genes, mcr-1 and a variant of mcr-3, on a single plasmid.
The E. coli strain was isolated from a chicken on a commercial farm in China. It is the first time that more than one mcr gene has been detected on one plasmid, according to research published in Antimicrobial Agents and Chemotherapy.
“The coexistence of mcr-1 and mcr-3 gene in E. coli isolates may pose a huge threat to public health and warrants further investigation,” Hong-Ning Wang, PhD, professor of animal disease prevention and food safety at Sichuan University, and colleagues wrote.
Mcr-1 is a plasmid-mediated resistance gene that first emerged in China in 2016, according to the researchers. It is resistant to colistin, a last-resort antibiotic. Since then, mcr-1 and four other mcr resistance genes (mcr-2, mcr-3 mcr-4 and mcr-5), as well as variants of these genes, have been identified in humans, food and food animals.
For the study, which is part of an ongoing surveillance effort, Wang and colleagues collected rectal swabs from chickens on several commercial farms in China to identify bacteria harboring mcr-1, according to a press release. DNA sequencing and PCR amplification revealed that one strain, E. coli ECSC102, carried both mcr-1 and a variant of mcr-3 on an IncP plasmid. The mcr-3 variant, named mcr-3.11, had two amino acid substitutions compared with the original gene.
E. coli ECSC102 was resistant to colistin, ampicillin, cefotaxime, ciprofloxacin, cefoxitin, trimethoprim-sulfamethoxazole, streptomycin and tetracycline. The strain was susceptible to imipenem, tigecycline, aztreonam and amikacin.
In conjugation experiments, the presence of both mcr-1 and mcr-3.11 in E. coli was associated with higher minimum inhibitory concentrations of colistin than the presence of either gene alone, according to the researchers. They further noted that the IncP plasmid carrying both genes “aligned very well” with two other mcr-carrying plasmids. One of these plasmids was found in an E. coli isolate from a hospitalized patient and the other was found in a Klebsiella pneumonia isolate that was recovered from hospital sewage.
“This study was originally designed to isolate strains carrying mcr-1 genes, but it is surprising that there are already strains carrying multiple mcr genes in chicken farms,” Wang said in a press release. “The apparent spread of the same IncP plasmid with one or two mcr genes between different species and a patient, the hospital environment, and animal production is worrying.” – by Stephanie Viguers
Disclosure: Infectious Disease News was unable to confirm relevant financial disclosures at the time of publication.
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