241. In Vitro Activity of Colistin (Polymyxin E) Versus Gram-negative Bacilli from Patients in Canadian Hospitals: Results of the CANWARD Study 2008-2010
Session: Poster Abstract Session: Antimicrobial Susceptibility and Resistance
Friday, October 21, 2011
Room: Poster Hall B1
Handouts
  • Walkty Colistin IDSA2011_Aug29.pdf (296.2 kB)
  • Background:  Multidrug-resistant (MDR = resistant to at least 3 different antimicrobial classes) Gram-negative bacilli often pose a therapeutic dilemma for clinicians due to limited treatment options.   The purpose of this study was to evaluate the in vitro activity of colistin (polymyxin E) against aerobic and facultative Gram-negative bacilli obtained from patients in Canadian hospitals (CANWARD).

    Methods:  From January 2008 through November 2010, tertiary-care centres from across Canada submitted pathogens from patients attending hospital clinics, emergency rooms, medical and surgical wards, and intensive care units.  Annually, each centre was asked to submit pathogens (consecutive, one per patient/infection site) from blood, respiratory, urine, and wound/IV infections.  Susceptibility testing was performed using CLSI broth microdilution. 

    Results:  The in vitro activity of colistin and comparator antimicrobials was evaluated versus 7046 Gram-negative bacilli. 

     

     

    MIC50/MIC90 (g/mL)

     

    n

    Colistin

    Ceftazidime

    Ciprofloxacin

    Gentamicin

    Enterobacteriaceae

    E. coli

    3247

    0.25/0.5

    ≤0.5/1

    ≤0.06/>16

    ≤0.5/4

    E. coli (ESBL)

    133

    0.5/0.5

    16/>32

    >16/>16

    2/>32

    K. pneumoniae

    978

    0.5/1

    ≤0.5/1

    ≤0.06/0.5

    ≤0.5/≤0.5

    K. pneumoniae (ESBL)

    22

    0.5/0.5

    16/>32

    4/>16

    1>32

    E. cloacae

    367

    0.5/>16

    0.5/>32

    ≤0.06/0.12

    ≤0.5/≤0.5

    P. mirabilis

    250

    >16/>16

    ≤0.5/≤0.5

    ≤0.06/2

    1/1

    K. oxytoca

    247

    0.5/1

    ≤0.5/0.5

    ≤0.06/0.12

    ≤0.5/≤0.5

    S. marcescens

    234

    >16/>16

    ≤0.5/1

    ≤0.06/1

    ≤0.5/1

    E. aerogenes

    95

    0.5/1

    0.5/>32

    ≤0.06/1

    ≤0.5/≤0.5

    C. freundii

    72

    0.5/0.5

    0.5/>32

    ≤0.06/1

    ≤0.5/8

    M. morganii

    64

    >16/>16

    ≤0.5/4

    ≤0.06/1

    ≤0.5/32

    Medically Important Non-fermentative Gram-negative Bacilli

    P. aeruginosa

    1219

    2/2

    4/32

    0.25/8

    4/16

    S. maltophilia

    206

    8/>16

    >32/>32

    2/16

    32/>32

    A. baumannii

    67

    1/2

    8/32

    0.12/2

    1/2

    The percentage of P. aeruginosa isolates susceptible to colistin (93% overall) did not change significantly over the 3 study years (p > 0.05).  Of 97 MDR P. aeruginosa isolates, 84 (87.6%) were susceptible to colistin.  All 4 MDR A. baumannii isolates were susceptible to colistin.

    Conclusion:  The MIC90 value of colistin versus E. coli and K. pneumoniae (including ESBL producers) was ≤1 g/mL.  Over 90% of P. aeruginosa and A. baumannii isolates remained susceptible to this antimicrobial.


    Subject Category: A. Antimicrobial agents and Resistance

    Andrew Walkty, MD1, Melanie Baxter, MSc1, Heather J. Adam, PhD2, Kim Nichol, MSc1, James Karlowsky, PhD1, Daryl J. Hoban, PhD1 and George G. Zhanel, PhD1, (1)University of Manitoba, Winnipeg, MB, Canada, (2)Department of Clinical Microbiology, Health Sciences Centre, Winnipeg, MB, Canada

    Disclosures:

    A. Walkty, None

    M. Baxter, None

    H. J. Adam, None

    K. Nichol, None

    J. Karlowsky, None

    D. J. Hoban, Abbott Laboratories Ltd: Research Relationship, Research support
    Astellas Pharma Canada Inc: Research Relationship, Research support
    Bayer Schering Pharma AG: Research Relationship, Research support
    Merck Frosst Canada Ltd.: Research Relationship, Research support
    Pfizer Canada Inc.: Research Relationship, Research support
    Sepracor Pharmaceuticals Inc.: Research Relationship, Research support
    The Medicines Company: Research Relationship, Research support

    G. G. Zhanel, Abbott Laboratories Ltd.: Research Relationship, Research support
    Astellas Pharma Canada Inc.: Research Relationship, Research support
    Bayer Shcering Pharma AG: Research Relationship, Research support
    Merck Frosst Canada Ltd.: Research Relationship, Research support
    Pfizer Canada Inc: Research Relationship, Research support
    Sepracor Pharmaceuticals Inc.: Research Relationship, Research support
    The Medicines Company: Research Relationship, Research support

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