TABLE 2.
Characterization of the 1st-step enrofloxacin-resistant clones selected in vitro
| Isolate (ST) | Resistant coloniesa |
QRDR mutation at indicated positionb |
Genotype | MIC (μg/ml)c |
||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ENR concn (μg/ml) | Recovery frequency (no. of clones) | Mutation distribution (no. of clones with mutation/total no. of clones) | GyrA |
GyrB |
ParC |
|||||||||
| 81 | 83 | 87 | 362 | 80 | 84 | 98 | ENR | DAN | MAR | |||||
| PG45 (ST1) | Gly | Ser | Glu | Asp | Ser | Asp | Thr | WT | 0.25 | 0.25 | 0.5 | |||
| 0.25 | 2E−05 (20) | 11/20 | GT1 | 0.25 | 1 | 0.5 | ||||||||
| 0.25 | 5/20 | Gly | NA | NA | NA | |||||||||
| 0.25 | 3/20 | Asn | NA | NA | NA | |||||||||
| 0.25 | 1/20 | Asn | Arg | NA | NA | NA | ||||||||
| 15762 (ST2) | Gly | Ser | Glu | Asn | Ser | Asp | Thr | WT | 0.25 | 0.5 | 1 | |||
| 0.25 | 3E−06 (20) | 20/20 | GT4 | 0.25 | 0.5 | 1 | ||||||||
| 15488 (ST2) | Gly | Ser | Glu | Asn | Ile | Asp | Thr | WT | 0.5 | 1 | 2 | |||
| 2 | 6E−07 (5) | 3/5 | Phe | 16 | 16 | >64 | ||||||||
| 2 | 1/5 | Tyr | NA | NA | NA | |||||||||
| 2 | 1/5 | Gly | NA | NA | NA | |||||||||
| 15875 (ST2) | Gly | Ser | Glu | Asn | Ser | Tyr | Thr | WT | 1 | 1 | 2 | |||
| 2 | 4E−07 (4) | 3/4 | Lys | 4 | 8 | 8 | ||||||||
| 2 | 1/4 | Phe | 4 | 8 | 8 | |||||||||
| 15527 (ST3) | Gly | Ser | Glu | Asn | Ser | Asp | Thr | WT | 0.5 | 0.5 | 2 | |||
| 0.5 | 7E−05 (12) | 1/12 | NA | NA | NA | |||||||||
| 0.5 | 6/12 | Val | NA | NA | NA | |||||||||
| 0.5 | 1/12 | Val | Gly | NA | NA | NA | ||||||||
| 0.5 | 2/12 | Phe | NA | NA | NA | |||||||||
| 0.5 | 1/12 | Phe | Asn | GT2 | 4 | 4 | 8 | |||||||
| 0.5 | 1/12 | Phe | Asn | Arg | GT3 | 4 | 2 | 8 | ||||||
| 8619 (ST3) | Gly | Ser | Glu | Asn | Ser | Asp | Thr | WT | 0.25 | 0.5 | 0.5 | |||
| 0.25 | 2E−06 (10) | 8/10 | NA | NA | NA | |||||||||
| 0.25 | 2/10 | Phe | GT5 | 1 | 2 | 1 | ||||||||
Resistant colonies were selected on plates containing enrofloxacin at the indicated concentrations. The recovery frequency was determined as the number of colonies appearing on the plate in the presence of enrofloxacin divided by the number of colonies contained in the inoculum.
Point mutations detected in QRDRs of gyrA, parC, and gyrB are presented as the corresponding amino acid substitutions in individual clones. For each isolate, the WT phenotype is shown first. The GT1, GT2, GT3, and GT4 genotypes were used to perform further selection steps. When the phenotype of an isolate differs from that of PG45T, the mutation is indicated in bold. Newly acquired mutations are underlined.
MIC of an ENR-resistant mutant representing the genotype. NA, not applicable (mutant not available in broth culture).