a Hôpital Maisonneuve-Rosemont, University of Montreal, 5415 LAssomption, Montreal, Quebec H1T 2M4; b Mount Sinai Hospital, University of Toronto, Toronto; c Montreal Children's Hospital, McGill University, Montreal; d Hôpital de lEnfant-Jesus, Laval University, Quebec City, Canada
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Abstract |
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Introduction |
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Materials and methods |
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From 1990 to 1998, all strains of S. pneumoniae isolated from sterile sites (blood, CSF, pleural or articular fluids) were stored and frozen at 70°C. Three large teaching tertiary care hospitals (two adult: Hôpital Maisonneuve-Rosemont, Montreal, and Hôpital de lEnfant-Jesus, Quebec City; and one paediatric: The Montreal Children's Hospital, Montreal) participated in the study. A total of 704 single clinical isolates of S. pneumoniae were included in this survey (634 blood, 51 CSF, 19 other). Patients comprised 390 males (55.3%) and 314 females (44.7%) with an age range of 0.1102 years and a median age of 33.2 years.
Strains were identified using standard procedures: Gram's stain, optochin susceptibility test and bile solubility test.
Antibiotics and susceptibility testing
Penicillin, cefuroxime and erythromycin were purchased from Nucrotechnics (Scarborough, Ontario, Canada). Clarithromycin and ABT-773 were provided by Abbott Canada (Montreal, Quebec, Canada). The isolates were tested against the following antibiotics at the following concentrations (mg/L): penicillin, 0.034; cefuroxime, 0.068; erythromycin, 0.068; clarithromycin, 0.068; and ABT-773, 0.068.
MICs were determined using a broth microdilution method according to NCCLS recommendations.4 A 0.5 McFarland equivalent suspension was prepared from an overnight sheep blood agar culture of S. pneumoniae. This solution was then diluted 1:10 to yield 107 cfu/mL. Five microlitres of this suspension was added to a cation-adjusted MuellerHinton supplemented with 5% lysed horse blood in order to reach a final concentration of 5 x 104 cfu/well. Trays were incubated at 35°C for 24 h in ambient air. The lowest concentration of antibiotic showing no growth was recorded as the MIC. Quality control was assessed by testing S. pneumoniae ATCC 49619.
For ABT-773, a recommended breakpoint for susceptibility of 0.5 mg/L was used.5
Determination of macrolide-resistance mechanisms
The macrolide-resistance mechanism was determined for 28 erythromycin-resistant S. pneumonia strains by PCR using specific primers as described previously.6
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Results and discussion |
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Acknowledgements |
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Notes |
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References |
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Received 28 March 2001; returned 14 June 2001; revised 25 June 2001; accepted 4 July 2001