Characterization ofPseudomonas aeruginosaIsolates Obtained from Patients in Canadian Hospitals: Results of the CANWARD 2007 Study

Pseudomonas aeruginosa is an important nosocomialpathogen. The purpose of the present study was to evaluate theantimicrobial susceptibility profile of P aeruginosa isolates obtainedfrom patients in different areas of Canadian hospitals.METHODS: From January to December 2007 inclusive, 12 sentinelhospitals across Canada submitted clinical isolates from patientsattending emergency rooms, medical wards, surgical wards and intensivecare 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 andLaboratory Standards Institute broth microdilution methods.Multidrug-resistant (MDR; resistant to at least three different antimicrobialclasses) isolates were typed by pulsed-field gel electrophoresis.RESULTS: In total, 451 P aeruginosa isolates were collected (representing7% of all CANWARD 2007 isolates). The rank order of antimicrobialsusceptibility 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, meropenemand levofloxacin was observed more frequently among ICU isolates(P<0.05). Thirty-four isolates (7.5%) were MDR. MDR isolates weremore likely to be obtained from patients in an ICU (P=0.003) and lesslikely to come from a bloodstream source (P=0.008). Excluding colistin(polymyxin E), amikacin and piperacillin/tazobactam, followed bymeropenem, were the most active antimicrobials evaluated versus theMDR 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 specimensfrom patients in Canadian hospitals. Of the antipseudomonal antimicrobialsevaluated, amikacin, meropenem and piperacillin/tazobactamdemonstrated the greatest in vitro activity. Isolates with reduced antimicrobialsusceptibility and MDR isolates were more often obtainedfrom ICU patients. All of the MDR isolates remained susceptible tocolistin