Journal Article

Are fluoroquinolone-susceptible isolates of <i>Streptococcus pneumoniae</i> really susceptible? A comparison of resistance mechanisms in Canadian isolates from 1997 and 2003

Kristen N. Schurek, Heather J. Adam, Christine G. Siemens, Chris J. Hoban, Daryl J. Hoban and George G. Zhanel

in Journal of Antimicrobial Chemotherapy

Published on behalf of British Society for Antimicrobial Chemotherapy

Volume 56, issue 4, pages 769-772
Published in print October 2005 | ISSN: 0305-7453
Published online August 2005 | e-ISSN: 1460-2091 | DOI: http://dx.doi.org/10.1093/jac/dki315
Are fluoroquinolone-susceptible isolates of Streptococcus pneumoniae really susceptible? A comparison of resistance mechanisms in Canadian isolates from 1997 and 2003

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Objectives: To assess the prevalence of efflux and amino acid substitutions in ParC and GyrA in Canadian clinical isolates of fluoroquinolone-susceptible Streptococcus pneumoniae with levofloxacin MICs of 1 mg/L collected before the introduction of the respiratory fluoroquinolones (1995–1997) and after 7 years of use (2003).

Methods: Quinolone resistance determining regions of parC and gyrA were sequenced for 111 clinical isolates collected from 1995 to 1997 and 665 isolates collected in 2003. Efflux was assessed using a reserpine agar dilution method.

Results: No isolates exhibited efflux. No significant increase in isolates harbouring amino acid substitutions was observed over time (0.9% in 1995–1997 to 2.1% in 2003, P = 0.32). However, the proportion of isolates with a ciprofloxacin MIC = 2 mg/L and a levofloxacin MIC = 1 mg/L versus ciprofloxacin MIC = 1 mg/L and a levofloxacin MIC = 1 mg/L increased over time (3.6% to 6.5%, P = 0.0021).

Conclusions: No increase in prevalence of first-step parC mutations was observed among all fluoroquinolone-susceptible clinical isolates of S. pneumoniae with levofloxacin MICs of 1 mg/L after the introduction of the respiratory fluoroquinolones; however, fluoroquinolones appear to be selecting for isolates with elevated ciprofloxacin MICs.

Keywords: levofloxacin; mutations; efflux

Journal Article.  2145 words. 

Subjects: Medical Oncology ; Critical Care

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