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Volume 9, Number 7—July 2003

Research

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 1

ParC amino acid substitutions found in 115 Streptococcus pneumoniae isolates with levofloxacin MICs >2 μg/mL and corresponding levofloxacin MICs

ParC amino acid substitution No. isolates inhibited by levofloxacin MIC (µg/mL) of
Total no. of strains
2 4 8 16 ≥32
Ser79→Phe 28 4 3 9 3 47
Ser79→Tyr 7 1 3 2 1 14
Ser79→Ala 1 0 0 0 0 1
Asp83→Asn 7 0 3 0 0 10
Asp83→Gly 1 0 0 0 0 1
Asp83→Tyr 3 0 0 0 0 3
Asp83→Val 1 0 0 0 0 1
Asp83→Ala 0 0 1 0 0 1
No. isolates/total with amino acid substitutions 48/82 (59%) 5/8a (63%) 10/10 11/11 4/4 78/115 (69%)

aOne isolate with no ParC amino acid substitution found to have active efflux; two isolates had ParC amino acid substitutions at sites other than Ser79 or Asp83.

Main Article

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