title: Frequency of MCR-1-mediated colistin resistance among Escherichia coli clinical isolates obtained from patients in Canadian hospitals (CANWARD 2008-2015).
abstract: BACKGROUND
  Colistin is often used as an antimicrobial of last resort for the treatment of infections caused by multidrug-resistant gram-negative bacilli. In 2015, plasmid-mediated colistin resistance inEscherichia colidue to MCR-1 was described. The purpose of this study was to evaluate the frequency of colistin resistance amongE. coliclinical isolates obtained from patients in Canadian hospitals as part of the Canadian Ward Surveillance Study (CANWARD) and to determine how often themcr-1gene is detected among the colistin-resistant subset.
  
  
  METHODS
  From January 2008 to December 2015 (excluding 2011), 10 to 15 sentinel hospitals submitted consecutive clinical isolates (1 per patient per infection site) from blood (100-240), respiratory (100-150), urine (25-100) and wound (25-100) infections. We performed susceptibility testing using Clinical and Laboratory Standards Institute broth microdilution methods. Isolates that showed resistance to colistin as defined by European Committee on Antimicrobial Susceptibility Testing breakpoints (minimum inhibitory concentration ≥ 4 µg/mL) were evaluated for themcr-1gene by polymerase chain reaction.
  
  
  RESULTS
  In total, 5571E. coliclinical isolates were obtained over the study years. Twelve isolates (0.2%) were resistant to colistin. The proportion of colistin-resistant isolates varied from 0.0% to 0.5% depending on the study year, and there was no clear trend toward increasing resistance over time. Typically the colistin-resistant isolates remained susceptible to antimicrobials from several other classes. Two colistin-resistant isolates (0.04%) were found to harbour themcr-1gene.
  
  
  CONCLUSIONS
  The results suggest that colistin resistance amongE. colihuman clinical isolates, including resistance mediated by themcr-1gene, remains rare in Canada.
authors.affiliation: Section of Infectious Diseases (Walkty), Department of Internal Medicine; Department of Medical Microbiology (Walkty, Karlowsky, Adam, Lagacé-Wiens, Baxter, Zhanel), University of Manitoba; Diagnostic Services Manitoba (Walkty, Karlowsky, Adam, Lagacé-Wiens); Public Health Agency of Canada (Mulvey, McCracken), Winnipeg, Man.; Department of Microbiology (Poutanen), University Health Network/Mount Sinai Hospital; Departments of Laboratory Medicine and Pathobiology and of Medicine (Poutanen), University of Toronto, Toronto, Ont.; Department of Microbiology (Roscoe), Vancouver Hospital, Vancouver, BC.
authors.forename: Andrew
authors.initials: A
authors.lastname: Walkty
authors.affiliation: Section of Infectious Diseases (Walkty), Department of Internal Medicine; Department of Medical Microbiology (Walkty, Karlowsky, Adam, Lagacé-Wiens, Baxter, Zhanel), University of Manitoba; Diagnostic Services Manitoba (Walkty, Karlowsky, Adam, Lagacé-Wiens); Public Health Agency of Canada (Mulvey, McCracken), Winnipeg, Man.; Department of Microbiology (Poutanen), University Health Network/Mount Sinai Hospital; Departments of Laboratory Medicine and Pathobiology and of Medicine (Poutanen), University of Toronto, Toronto, Ont.; Department of Microbiology (Roscoe), Vancouver Hospital, Vancouver, BC.
authors.forename: James A
authors.initials: JA
authors.lastname: Karlowsky
authors.affiliation: Section of Infectious Diseases (Walkty), Department of Internal Medicine; Department of Medical Microbiology (Walkty, Karlowsky, Adam, Lagacé-Wiens, Baxter, Zhanel), University of Manitoba; Diagnostic Services Manitoba (Walkty, Karlowsky, Adam, Lagacé-Wiens); Public Health Agency of Canada (Mulvey, McCracken), Winnipeg, Man.; Department of Microbiology (Poutanen), University Health Network/Mount Sinai Hospital; Departments of Laboratory Medicine and Pathobiology and of Medicine (Poutanen), University of Toronto, Toronto, Ont.; Department of Microbiology (Roscoe), Vancouver Hospital, Vancouver, BC.
authors.forename: Heather J
authors.initials: HJ
authors.lastname: Adam
authors.affiliation: Section of Infectious Diseases (Walkty), Department of Internal Medicine; Department of Medical Microbiology (Walkty, Karlowsky, Adam, Lagacé-Wiens, Baxter, Zhanel), University of Manitoba; Diagnostic Services Manitoba (Walkty, Karlowsky, Adam, Lagacé-Wiens); Public Health Agency of Canada (Mulvey, McCracken), Winnipeg, Man.; Department of Microbiology (Poutanen), University Health Network/Mount Sinai Hospital; Departments of Laboratory Medicine and Pathobiology and of Medicine (Poutanen), University of Toronto, Toronto, Ont.; Department of Microbiology (Roscoe), Vancouver Hospital, Vancouver, BC.
authors.forename: Philippe
authors.initials: P
authors.lastname: Lagacé-Wiens
authors.affiliation: Section of Infectious Diseases (Walkty), Department of Internal Medicine; Department of Medical Microbiology (Walkty, Karlowsky, Adam, Lagacé-Wiens, Baxter, Zhanel), University of Manitoba; Diagnostic Services Manitoba (Walkty, Karlowsky, Adam, Lagacé-Wiens); Public Health Agency of Canada (Mulvey, McCracken), Winnipeg, Man.; Department of Microbiology (Poutanen), University Health Network/Mount Sinai Hospital; Departments of Laboratory Medicine and Pathobiology and of Medicine (Poutanen), University of Toronto, Toronto, Ont.; Department of Microbiology (Roscoe), Vancouver Hospital, Vancouver, BC.
authors.forename: Melanie
authors.initials: M
authors.lastname: Baxter
authors.affiliation: Section of Infectious Diseases (Walkty), Department of Internal Medicine; Department of Medical Microbiology (Walkty, Karlowsky, Adam, Lagacé-Wiens, Baxter, Zhanel), University of Manitoba; Diagnostic Services Manitoba (Walkty, Karlowsky, Adam, Lagacé-Wiens); Public Health Agency of Canada (Mulvey, McCracken), Winnipeg, Man.; Department of Microbiology (Poutanen), University Health Network/Mount Sinai Hospital; Departments of Laboratory Medicine and Pathobiology and of Medicine (Poutanen), University of Toronto, Toronto, Ont.; Department of Microbiology (Roscoe), Vancouver Hospital, Vancouver, BC.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Mulvey
authors.affiliation: Section of Infectious Diseases (Walkty), Department of Internal Medicine; Department of Medical Microbiology (Walkty, Karlowsky, Adam, Lagacé-Wiens, Baxter, Zhanel), University of Manitoba; Diagnostic Services Manitoba (Walkty, Karlowsky, Adam, Lagacé-Wiens); Public Health Agency of Canada (Mulvey, McCracken), Winnipeg, Man.; Department of Microbiology (Poutanen), University Health Network/Mount Sinai Hospital; Departments of Laboratory Medicine and Pathobiology and of Medicine (Poutanen), University of Toronto, Toronto, Ont.; Department of Microbiology (Roscoe), Vancouver Hospital, Vancouver, BC.
authors.forename: Melissa
authors.initials: M
authors.lastname: McCracken
authors.affiliation: Section of Infectious Diseases (Walkty), Department of Internal Medicine; Department of Medical Microbiology (Walkty, Karlowsky, Adam, Lagacé-Wiens, Baxter, Zhanel), University of Manitoba; Diagnostic Services Manitoba (Walkty, Karlowsky, Adam, Lagacé-Wiens); Public Health Agency of Canada (Mulvey, McCracken), Winnipeg, Man.; Department of Microbiology (Poutanen), University Health Network/Mount Sinai Hospital; Departments of Laboratory Medicine and Pathobiology and of Medicine (Poutanen), University of Toronto, Toronto, Ont.; Department of Microbiology (Roscoe), Vancouver Hospital, Vancouver, BC.
authors.forename: Susan M
authors.initials: SM
authors.lastname: Poutanen
authors.affiliation: Section of Infectious Diseases (Walkty), Department of Internal Medicine; Department of Medical Microbiology (Walkty, Karlowsky, Adam, Lagacé-Wiens, Baxter, Zhanel), University of Manitoba; Diagnostic Services Manitoba (Walkty, Karlowsky, Adam, Lagacé-Wiens); Public Health Agency of Canada (Mulvey, McCracken), Winnipeg, Man.; Department of Microbiology (Poutanen), University Health Network/Mount Sinai Hospital; Departments of Laboratory Medicine and Pathobiology and of Medicine (Poutanen), University of Toronto, Toronto, Ont.; Department of Microbiology (Roscoe), Vancouver Hospital, Vancouver, BC.
authors.forename: Diane
authors.initials: D
authors.lastname: Roscoe
authors.affiliation: Section of Infectious Diseases (Walkty), Department of Internal Medicine; Department of Medical Microbiology (Walkty, Karlowsky, Adam, Lagacé-Wiens, Baxter, Zhanel), University of Manitoba; Diagnostic Services Manitoba (Walkty, Karlowsky, Adam, Lagacé-Wiens); Public Health Agency of Canada (Mulvey, McCracken), Winnipeg, Man.; Department of Microbiology (Poutanen), University Health Network/Mount Sinai Hospital; Departments of Laboratory Medicine and Pathobiology and of Medicine (Poutanen), University of Toronto, Toronto, Ont.; Department of Microbiology (Roscoe), Vancouver Hospital, Vancouver, BC.
authors.forename: George G
authors.initials: GG
authors.lastname: Zhanel