| Summary: | BACKGROUND: Community-associated methicillin-resistant
Staphylococcus aureus (CA-MRSA) differ from health care-associated
MRSA (HA-MRSA) in their genotypic and phenotypic characteristics.
The purpose of the present study was to compare the demographics,
antimicrobial susceptibilities and molecular epidemiology of
CA-MRSA and HA-MRSA in Canada.
METHODS: In 2007, 385 MRSA isolates were collected from
Canadian patients attending hospital clinics, emergency rooms, medical/
surgical wards and intensive care units. Susceptibilities to betalactams,
clarithromycin, clindamycin, daptomycin, levofloxacin,
linezolid, moxifloxacin, tigecycline, trimethoprim-sulfamethoxazole
and vancomycin were determined by Clinical and Laboratory
Standards Institute broth microdilution. Strain typing was performed
by pulsed-field gel electrophoresis (PFGE) and the mecA, nuc and pvl
genes were detected by polymerase chain reaction.
RESULTS: Of the 385 MRSA, 19.5% were CA-MRSA and 79.2%
were HA-MRSA as determined by PFGE. CA-MRSA belonged to
PFGE types CMRSA10/USA300 (66.7%) and CMRSA7/USA400
(33.3%); PFGE types identified among HA-MRSA included
CMRSA2/USA100/800 (81.6%), CMRSA6 (13.1%), CMRSA1/
USA600 (3.3%), CMRSA5/USA500 (1.3%), CMRSA3 (0.3%) and
CMRSA9 (0.3%). Panton-Valentine leukocidin (PVL) was detected
in 94.7% of CA-MRSA and 0.7% of HA-MRSA. Resistance rates
(CA-MRSA versus HA-MRSA) were 61.3% versus 97.7% to levofloxacin,
73.3% versus 96.7% to clarithromycin, 12.0% versus 74.8% to
clindamycin and 0.0% versus 15.4% to trimethoprim-sulfamethoxazole.
No MRSA were resistant to vancomycin, linezolid, tigecycline or
daptomycin.
CONCLUSIONS: CA-MRSA represented 19.5% of all MRSA.
CA-MRSA was significantly more susceptible to levofloxacin,
clarithromycin, clindamycin and trimethoprim-sulfamethoxazole than
HA-MRSA. Of CA-MRSA, 94.7% were PVL-positive while 99.3% of
HA-MRSA were PVL-negative. CA-MRSA is an emerging pathogen
in Canadian hospitals.
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