Abstract:
INTRODUCTION: Pseudomonas aeruginosa is an important nosocomial
pathogen. The purpose of the present study was to evaluate the
antimicrobial susceptibility profile of P aeruginosa isolates obtained
from patients in different areas of Canadian hospitals.
METHODS: From January to December 2007 inclusive, 12 sentinel
hospitals across Canada submitted clinical isolates from patients
attending emergency rooms, medical wards, surgical wards and intensive
care units (ICUs) (the Canadian Ward Surveillance Study
[CANWARD 2007]). Each centre was asked to submit clinical isolates
(consecutive, one per patient per infection site) from blood (n=360),
respiratory (n=200), urine (n=100) and wound/intravenous (n=50)
infections. Susceptibility testing was performed using Clinical and
Laboratory Standards Institute broth microdilution methods.
Multidrug-resistant (MDR; resistant to at least three different antimicrobial
classes) isolates were typed by pulsed-field gel electrophoresis.
RESULTS: In total, 451 P aeruginosa isolates were collected (representing
7% of all CANWARD 2007 isolates). The rank order of antimicrobial
susceptibility was as follows (percent susceptible): amikacin
(93.1%) = piperacillin/tazobactam (93.1%) > meropenem (87.4%) >
cefepime (69.4%) > ciprofloxacin (67.2%) > gentamicin (66.1%) >
levofloxacin (60.5%). Reduced susceptibility to cefepime, meropenem
and levofloxacin was observed more frequently among ICU isolates
(Pud_less_than0.05). Thirty-four isolates (7.5%) were MDR. MDR isolates were
more likely to be obtained from patients in an ICU (P=0.003) and less
likely to come from a bloodstream source (P=0.008). Excluding colistin
(polymyxin E), amikacin and piperacillin/tazobactam, followed by
meropenem, were the most active antimicrobials evaluated versus the
MDR isolates. All of the MDR isolates were susceptible to colistin.
The majority of MDR isolates were genetically unrelated.
CONCLUSIONS: P aeruginosa is common among clinical specimens
from patients in Canadian hospitals. Of the antipseudomonal antimicrobials
evaluated, amikacin, meropenem and piperacillin/tazobactam
demonstrated the greatest in vitro activity. Isolates with reduced antimicrobial
susceptibility and MDR isolates were more often obtained
from ICU patients. All of the MDR isolates remained susceptible to
colistin.
