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 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.
