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Volume 9, Number 7—July 2003


Antimicrobial Susceptibility Breakpoints and First-Step parC Mutations in Streptococcus pneumoniae: Redefining Fluoroquinolone Resistance

Sue Lim*†, Darrin Bast*†, Allison McGeer*†, Joyce de Azavedo*†, and Donald E. Low*†Comments to Author 
Author affiliations: *Toronto Medical Laboratories/Mount Sinai Hospital, Toronto, Ontario, Canada; †University of Toronto, Toronto, Ontario, Canada

Main Article

Table 4

Characterization of Streptococcus pneumoniae isolates with levofloxacin MIC 4 μg/mLa

Isolate no. Amino acid substitution
Change in MIC
with inhibition of efflux
In ParC In GyrA
1 Ser79→Phe None 8-fold
2 Ser79→Phe None No effect
3 Asp78→Asn Ser81→Phe No effect
4 Ala115→Pro Ser81→Phe No effect
5 Ser79→Phe None No effect
6 Ser79→Phe None No effect
7 None None 4-fold
8 Ser79→Phe Ser81→Phe No effect

aparE and gyrB sequencing was performed on all isolates, but no mutations were found in the quinolone-resistance–determining region.

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