1826. In Vitro Activity of Colistin (Polymyxin E) Versus 2541 Pseudomonas aeruginosa Clinical Isolates Obtained from Patients in Canadian Hospitals: Results of the CANWARD Study, 2008-2014
Session: Poster Abstract Session: Treatment of HAIs/Antimicrobial Resistant Infections
Saturday, October 10, 2015
Room: Poster Hall

Background: Clinicians have limited therapeutic options from which to choose for the treatment of infections caused by multidrug-resistant Pseudomonas aeruginosa (MDR = non-susceptible to at least one antimicrobial from three or more different classes). Colistin, a polymyxin antimicrobial, is sometimes used as an agent of last resort. The purpose of this study was to evaluate the in vitro activity of colistin (polymyxin E) against a large collection of P. aeruginosa clinical isolates obtained from patients in Canadian hospitals (CANWARD, 2008 to 2014).

Methods: From January 2008 to December 2014, inclusive, 10 to 15 sentinel hospitals across Canada submitted clinical isolates from patients attending ERs, medical and surgical wards, hospital clinics, and ICUs (CANWARD). Each center was asked to submit clinical isolates (consecutive, one per patient/infection site) from blood (100 to 240), respiratory (100 to 150), urine (25 to 100), and wound (25 to 100) infections. Susceptibility testing was performed using broth microdilution as described by CLSI.

Results: The in vitro activity of colistin and comparator antimicrobials was evaluated versus 2541 P. aeruginosa clinical isolates (table below).

Antimicrobial

MIC50

(g/mL)

MIC90

(g/mL)

Susceptibility Breakpoint

(g/mL)

% Susceptible

Amikacin

4

16

≤16

93.4

Ceftazidime

4

32

≤8

83.3

Ciprofloxacin

0.25

4

≤1

76.1

Colistin

1

2

≤2

94.5

Gentamicin

2

16

≤4

81.9

Meropenem

0.5

8

≤2

81.0

Piperacillin-

Tazobactam

4

64

≤16/4

84.2

Three-hundred and seventy-one isolates (14.6% of all isolates tested) were MDR. Of these, 92.2% were susceptible to colistin. Among 140 colistin non-susceptible isolates (5.5% of all isolates tested), 79.3% remained fully susceptible to antimicrobials from three or more antipseudomonal antimicrobial classes.

Conclusion: Colistin demonstrated potent in vitro activity against P. aeruginosa clinical isolates, including those with an MDR phenotype. Isolates that were non-susceptible to colistin typically remained susceptible to multiple other antipseudomonal antimicrobials, indicating a lack of cross resistance.

Andrew Walkty, MD1,2, Heather J. Adam, PhD1,2, Melanie Baxter, MSc2, Philippe Lagace-Wiens, MD1,2, James Karlowsky, PhD1,2, Daryl Hoban, PhD1 and George Zhanel, PhD2, (1)Microbiology, Diagnostic Services Manitoba, Winnipeg, MB, Canada, (2)Medical Microbiology, University of Manitoba, Winnipeg, MB, Canada

Disclosures:

A. Walkty, None

H. J. Adam, None

M. Baxter, None

P. Lagace-Wiens, None

J. Karlowsky, None

D. Hoban, Abbott: research relationship , Research support
Achaogen: research relationship , Research support
Affinium: research relationship , Research support
AstraZeneca: research relationship , Research support
Astellas: research relationship , Research support
Cerexa: research relationship , Research support
Cubist: research relationship , Research support
Galderma: research relationship , Research support
Janssen Ortho Inc: research relationship , Research support
Merck: research relationship , Research support
Novexel: research relationship , Research support
Paladin Labs: research relationship , Research support
Pfizer: research relationship , Research support
Pharmascience Inc: research relationship , Research support
Sunovion: research relationship , Research support
Targanta: research relationship , Research support
Tetraphase: research relationship , Research support
The Medicines Company: research relationship , Research support
Theravance: research relationship , Research support
Wyeth: research relationship , Research support
Zoetis: research relationship , Research support

G. Zhanel, Abbott: research relationship , Research support
Achaogen: research relationship , Research support
Affinium: research relationship , Research support
Astellas: research relationship , Research support
AstraZeneca: research relationship , Research support
Cerexa: research relationship , Research support
Cubist: research relationship , Research support
Galderma: research relationship , Research support
Janssen Ortho Inc: research relationship , Research support
Merck: research relationship , Research support
Merck: research relationship , Research support
Novexel: research relationship , Research support
Paladin Labs: research relationship , Research support
Pfizer: research relationship , Research support
Pharmascience Inc: research relationship , Research support
Sunovion: research relationship , Research support
Targanta: research relationship , Research support
Tetraphase: research relationship , Research support
The Medicines Company: research relationship , Research support
Theravance: research relationship , Research support
Wyeth: research relationship , Research support
Zoetis: research relationship , Research support

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