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*†
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.
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