Co-occurrence of #mcr1 and #mcr3 #genes in a single #Escherichia coli in #NZ (J Antimicrob Chemother., abstract)

[Source: Journal of Antimicrobial Chemotherapy, full page: (LINK). Abstract, edited.]

Co-occurrence of mcr-1 and mcr-3 genes in a single Escherichia coli in New Zealand

Julie Creighton, Trevor Anderson, Julia Howard, Kristin Dyet, Xiaoyun Ren,Joshua Freeman

Journal of Antimicrobial Chemotherapy, dkz311,

Published: 24 July 2019

Issue Section: Research letter



The discovery of the plasmid-mediated colistin resistance gene mcr-1, first identified in 2015 among both clinical and animal isolates in China, raised concerns about pan-resistant bacteria.1 A plethora of publications quickly followed, suggesting mcr-1 was already established in many countries and across many continents, in various bacterial species, on a variety of plasmids types, and in bacteria isolated from diverse animal species, environmental sources and human health settings.2 Furthermore, several other mcr-like genes and gene variants have since been discovered.2,3

Colistin is among a diminishing group of antimicrobial agents available for…



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Keywords: Antibiotics; Drugs Resistance; Colistin; E. Coli; New Zealand.


Identification of Novel Mobilized #Colistin #Resistance #Gene #mcr9 in a #MDR, Colistin-Susceptible #Salmonella enterica Serotype #Typhimurium Isolate (mBio, abstract)

[Source: mBio, full page: (LINK). Abstract, edited.]

Identification of Novel Mobilized Colistin Resistance Gene mcr-9 in a Multidrug-Resistant, Colistin-Susceptible Salmonella enterica Serotype Typhimurium Isolate

Laura M. Carroll, Ahmed Gaballa, Claudia Guldimann, Genevieve Sullivan, Lory O. Henderson, Martin Wiedmann

Mark S. Turner, Editor

DOI: 10.1128/mBio.00853-19



Mobilized colistin resistance (mcr) genes are plasmid-borne genes that confer resistance to colistin, an antibiotic used to treat severe bacterial infections. To date, eight known mcrhomologues have been described (mcr-1 to -8). Here, we describe mcr-9, a novel mcrhomologue detected during routine in silico screening of sequenced Salmonella genomes for antimicrobial resistance genes. The amino acid sequence of mcr-9, detected in a multidrug-resistant (MDR) Salmonella enterica serotype Typhimurium (S. Typhimurium) strain isolated from a human patient in Washington State in 2010, most closely resembled mcr-3, aligning with 64.5% amino acid identity and 99.5% coverage using Translated Nucleotide BLAST (tblastn). The S. Typhimurium strain was tested for phenotypic resistance to colistin and was found to be sensitive at the 2-mg/liter European Committee on Antimicrobial Susceptibility Testing breakpoint under the tested conditions. mcr-9 was cloned in colistin-susceptible Escherichia coliNEB5α under an IPTG (isopropyl-β-d-thiogalactopyranoside)-induced promoter to determine whether it was capable of conferring resistance to colistin when expressed in a heterologous host. Expression of mcr-9 conferred resistance to colistin in E. coli NEB5α at 1, 2, and 2.5 mg/liter colistin, albeit at a lower level than mcr-3. Pairwise comparisons of the predicted protein structures associated with all nine mcr homologues (Mcr-1 to -9) revealed that Mcr-9, Mcr-3, Mcr-4, and Mcr-7 share a high degree of similarity at the structural level. Our results indicate that mcr-9 is capable of conferring phenotypic resistance to colistin in Enterobacteriaceae and should be immediately considered when monitoring plasmid-mediated colistin resistance.



Colistin is a last-resort antibiotic that is used to treat severe infections caused by MDR and extensively drug-resistant (XDR) bacteria. The World Health Organization (WHO) has designated colistin as a “highest priority critically important antimicrobial for human medicine” (WHO, Critically Important Antimicrobials for Human Medicine, 5th revision, 2017,, as it is often one of the only therapies available for treating serious bacterial infections in critically ill patients. Plasmid-borne mcr genes that confer resistance to colistin pose a threat to public health at an international scale, as they can be transmitted via horizontal gene transfer and have the potential to spread globally. Therefore, the establishment of a complete reference of mcr genes that can be used to screen for plasmid-mediated colistin resistance is essential for developing effective control strategies.

Keywords: Antibiotics; Drugs Resistance; Enterobacteriaceae; Salmonella enterica; MCR9; MCR3; Colistin; USA; Plasmids.


Molecular #epidemiology of isolates with multiple #mcr #plasmids from a #pig #farm in #GB: the effects of #colistin withdrawal in the short and long term (J Antimicrob Chemother., abstract)

[Source: Journal of Antimicrobial Chemotherapy, full page: (LINK). Abstract, edited.]

Molecular epidemiology of isolates with multiple mcr plasmids from a pig farm in Great Britain: the effects of colistin withdrawal in the short and long term

Nicholas A Duggett, Luke P Randall, Robert A Horton, Fabrizio Lemma, Miranda Kirchner, Javier Nunez-Garcia, Camilla Brena, Susanna M Williamson, Christopher Teale, Muna F Anjum

Journal of Antimicrobial Chemotherapy, dky292,

Published: 14 August 2018




The environment, including farms, might act as a reservoir for mobile colistin resistance (mcr) genes, which has led to calls for reduction of usage in livestock of colistin, an antibiotic of last resort for humans.


To establish the molecular epidemiology of mcr Enterobacteriaceae from faeces of two cohorts of pigs, where one group had initially been treated with colistin and the other not, over a 5 month period following stoppage of colistin usage on a farm in Great Britain; faecal samples were also taken at ∼20 months.


mcr-1 Enterobacteriaceae were isolated from positive faeces and was WGS performed; conjugation was performed on selected Escherichia coli and colistin MICs were determined.


E. coli of diverse ST harbouring mcr-1 and multiple resistance genes were isolated over 5 months from both cohorts. Two STs, from treated cohorts, contained both mcr-1 and mcr-3 plasmids, with some isolates also harbouring multiple copies of mcr-1 on different plasmids. The mcr-1 plasmids grouped into four Inc types (X4, pO111, I2 and HI2), with mcr-3 found in IncP. Multiple copies of mcr plasmids did not have a noticeable effect on colistin MIC, but they could be transferred simultaneously to a Salmonella host in vitro. Neither mcr-1nor mcr-3 was detected in samples collected ∼20 months after colistin cessation.


We report for the first known time on the presence in Great Britain of mcr-3from MDR Enterobacteriaceae, which might concurrently harbour multiple copies of mcr-1 on different plasmids. However, control measures, including stoppage of colistin, can successfully mitigate long-term on-farm persistence.


Keywords: Antibiotics; Drugs Resistance; Colistin; MCR1; MCR3; UK; Pigs; Enterobacteriaceae.


Molecular Insights into Functional Differences Between #mcr3- and #mcr1-Mediated #Colistin #Resistance (Antimicrob Agents Chemother., abstract)

[Source: Antimicrobial Agents and Chemotherapy, full page: (LINK). Abstract, edited.]

Molecular Insights into Functional Differences Between mcr-3- and mcr-1-Mediated Colistin Resistance

Hui Li a,b, Lu Yang a, Zhihai Liu a, Wenjuan Yin a, Dejun Liu a, Yingbo Shen a, Timothy Walsh c, Bing Shao a,b# and Yang Wang d#

Author Affiliations: a Beijing Advanced Innovation Center for Food Nutrition and Human Health, College of Veterinary Medicine, China Agricultural University, Beijing, P. R. China. b Beijing Key Laboratory of Diagnostic and Traceability Technologies for Food Poisoning, Beijing Center for Disease Prevention and Control, Beijing, P. R. China.  c Department of Medical Microbiology and Infectious Disease, Division of Infection and Immunity, Cardiff University, Cardiff, UK. d Beijing Key Laboratory of Detection Technology for Animal-Derived Food Safety, China Agricultural University, Beijing, P. R. China.



The global emergence of plasmid-mediated colistin resistance genes mcr-1 and mcr-3 has threatened the role of the “last resort” drug colistin in the defense against infections caused by multidrug-resistant Gram-negative bacteria. However, functional differences between these two genes in mediating colistin resistance remains poorly understood. Protein sequence alignment of MCR-3 and MCR-1 was therefore conducted in Clustal Omega to identify sequence divergence. The molecular recognition of lipid A head group phosphatidylethanolamine and MCR-3 enzyme was studied by homology modeling and molecular docking, with the catalytic mechanism of MCR-3 also being explored. Thr277 in MCR-3 was validated as the key amino acid residue responsible for the catalytic reaction using site-directed mutagenesis and was shown to act as a nucleophile. Lipid A modification induced by the MCR-3 and MCR-1 enzymes was confirmed by electrospray ionization time-of-flight mass spectrometry. Far-UV circular dichroism spectra of the MCR-3 and MCR-1 enzymes suggested that MCR-3 was more thermostable than MCR-1, with a melting temperature of 66.19°C compared with 61.14°C for MCR-1. These data provided molecular insight into the functional differences between mcr-3 and mcr-1 in conferring colistin resistance.



#Address correspondence to Bing Shao or Yang Wang

Copyright © 2018 American Society for Microbiology. All Rights Reserved.

Keywords: Antibiotics; Drugs Resistance; Colistin; MCR1; MCR3.


Prevalence and genetic analysis of #mcr3-positive #Aeromonas species from #humans, retail #meat, and environmental #water samples (Antimicrob Agents Chemother., abstract)

[Source: Antimicrobial Agents and Chemotherapy, full page: (LINK). Abstract, edited.]

Prevalence and genetic analysis of mcr-3-positive Aeromonas species from humans, retail meat, and environmental water samples

Yingbo Shen1, Chunyan Xu1, Qiaoling Sun2, Stefan Schwarz3, Yanran Ou1, Lu Yang1, Zixian Huang2, Inga Eichhorn3, Timothy R. Walsh4, Yang Wang1, Rong Zhang2 and Jianzhong Shen1#

Author Affiliations: 1 Beijing Advanced Innovation Center for Food Nutrition and Human Health, China Agricultural University, Beijing, China. 2 The Second Affiliated Hospital of Zhejiang University, Zhejiang University, Hangzhou, China. 3 Institute of Microbiology and Epizootics, Centre for Infection Medicine, Department of Veterinary Medicine, Freie Universität Berlin, Berlin, Germany. 4 Department of Medical Microbiology and Infectious Disease, Institute of Infection & Immunity, UHW Main Building, Heath Park Hospital, Cardiff



The mobile colistin-resistance gene mcr-3 is globally disseminated in both Enterobacteriaceae and Aeromonas species, the latter of which potentially serves as a reservoir for this gene. Here, we investigated the prevalence of mcr-3 from rectal swabs of humans, food-producing animals and their products, and the aquatic environment, and investigated the genetic relationships between the mcr-3-positive isolates. An enriched broth screening method was used to detect mcr-3in samples, and species identification of isolates from the positive samples was carried out by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and shotgun sequencing. All mcr-3-positive isolates were subjected to antimicrobial susceptibility testing, conjugation, and whole genome sequencing. Ten Aeromonas isolates, two from human rectal swabs, one from pork, three from chicken meat, and four from the aquatic environment, were positive for mcr-3, but only two showed resistance to colistin. Besides the mcr-3-variants identified before– the novel variants were termed mcr-3.13 to mcr-3.18 – all isolates also harbored mcr-3-like genes downstream of the mcr-3 variants. The MCR-3.13 to MCR-3.18 proteins exhibited only 84–85% amino acid identity to the original MCR-3 protein. Whole genome sequence analysis indicated diversity within the genetic environment of mcr-3-positive Aeromonas isolates, and possible transmission between different sources in China, and even worldwide. Close relationships between mcr-3-positive and -negative Aeromonas isolates suggested that mcr-3might be common in Aeromonas species, which are not inherent hosts of mcr-3but may act as an important reservoir of this mobile colistin-resistance gene.



#Address correspondence to Jianzhong Shen,

Copyright © 2018 American Society for Microbiology. All Rights Reserved.

Keywords: Antibiotics; Drugs Resistance; MCR3; Colistin; Poultry; Human; Food Safety; China.


Co-location of the #polymyxin #resistance gene #mcr1 and variant of #mcr3 on a #plasmid in #Escherichia colifrom #chicken farm (Antimicrob Agents Chemother., abstract)

[Source: Antimicrobial Agents and Chemotherapy, full page: (LINK). Abstract, edited.]

Co-location of the polymyxin resistance gene mcr-1 and variant of mcr-3 on a plasmid in Escherichia colifrom chicken farm

Rong Xiang,  Bi-Hui Liu, An-Yun Zhang, Chang-Wei Lei, Xiao-Lan Ye, Yan-Xian Yang, Yan-Peng Chen and Hong-Ning Wang*

Author Affiliations: Animal Disease Prevention and Food Safety Key Laboratory of Sichuan Province, Key Laboratory of Bio-Resource and Eco-Environment of Ministry of Education, College of Life Sciences, Sichuan University, Chengdu 610065, Sichuan, P.R.China



A colistin-resistant Escherichia coli from commercial poultry farm in China carried two colistin-resistance genes mcr-1 and variant of mcr-3 in an IncP plasmid. The variant of mcr-3 gene, named mcr-3.11, encoded two amino acid substitutions compared with the mcr-3. A novel genetic structure, ISKpn40-mcr-3-dgkA- ISKpn40, might be the key element mediating translocation of mcr-3 through the formation of circular form. The mcr-1 and mcr-3 genes co-located on a plasmid might pose huge threat to public health.



*Corresponding author. Mailing address: College of Life science, Sichuan University, NO. 29 Wangjiang Road, Chengdu, Sichuan, China, 610064., Phone: +86-28-8547-1599. Fax: +86-28-8547-1599., E-mail:

Copyright © 2018 American Society for Microbiology. All Rights Reserved.

Keywords: Antibiotics; Drugs Resistance; E. Coli; Polymyxins; MCR1; MCR3; Poultry; China.


#Genetic and functional characterization of an #MCR3-like producing Escherichia #coli recovered from #swine, #Brazil (Antimicrob Agents Chemother., abstract)

[Source: Antimicrobial Agents and Chemotherapy, full page: (LINK). Abstract, edited.]

Genetic and functional characterization of an MCR-3-like producing Escherichia coli recovered from swine, Brazil

Nicolas Kieffer1,2,  Patrice Nordmann1,2,3,4,  Andrea Micke Moreno5, Luisa Zanolli Moreno5,  Richard Chaby6,  Aude Breton6,  Pierre Tissières6 and Laurent Poirel1,2,4*

Author Affiliations: 1 Medical and Molecular Microbiology Unit, Department of Medicine, Faculty of Science, University of Fribourg, Fribourg, Switzerland; 2 INSERM European Unit (IAME, France), University of Fribourg, Fribourg, Switzerland; 3 Institute for Microbiology, University of Lausanne and University Hospital Centre, Lausanne, Switzerland; 4 Swiss National Reference Center for Emerging Antibiotic Resistance (NARA), University of Fribourg, Switzerland; 5 Departamento de Medicina Veterinária Preventiva e Saúde Animal, Faculdade de Medicina Veterinária e Zootecnia, São Paulo, Brazil; 6 Institute for integrative biology of the cell (I2BC), CEA, CNRS, Université Paris-Sud, Université Paris-Saclay, Orsay, France



A collection of 126 pigs were screened for carriage of colistin-resistant Enterobacteriaceae in a farm in Minas Gerais, Brazil. Out of this collection, eigth colistin-resistant Escherichia coli isolates were recovered, including one from Minas Gerais State, producing a new MCR-3 variant (MCR-3.12). Analysis of the lipopolysaccharide revealed that MCR-3.12 had a similar function as MCR-1 and MCR-2 by adding a phosphoethanolamine group to the lipid A. Genetic analysis showed that the mcr-3.12 gene was carried by an IncA/C2 plasmid and was embedded in an original genetic environment. This study reports the occurrence of the MCR-3-like determinant in South America and firstly demonstrates the functionality of this group of enzymes as a phosphoethanolamine transferase.



*Corresponding author. Mailing address: Medical and Molecular Microbiology Unit, Department of Medicine, Faculty of Science, University of Fribourg, Chemin du Musée 18, CH-1700 Fribourg, Switzerland. Phone: 41-26-300-9582. E-mail:

Copyright © 2018 American Society for Microbiology. All Rights Reserved.

Keywords: Antibiotics; Drugs Resistance; Colistin; E. Coli; Pigs; Brazil.