TABLE 4.
Quinolone resistance phenotypes and mutations of all the isolates selected in vivo in chickens treated with four successive doses of enrofloxacin
| Time of isolation (dose [μg/ml]) | No. of isolates | MIC for the most resistant isolates (μg/ml)a
|
No. of isolates with gyrA mutation(s) at indicated codon/totalb
|
No. of isolates with parC mutations at codon 80 (Ser)c | |||||
|---|---|---|---|---|---|---|---|---|---|
| Nal | Flu | Enr | Cip | 81 (Gly) | 83 (Ser) | 87 (Asp) | |||
| Before treatment | 5 | 32 | 8 | 1 | 0.125 | None | None | None | ND |
| After treatment: | |||||||||
| 1 (6.25) | 27 | >1,024 | 128 | 4 | 2 | None | 26/27 | 1/27 | None |
| 2 (12.5) | 29 | >1,024 | 512 | 16 | 4 | None | 29/29 | None | None |
| 3 (25) | 20 | >1,024 | 512 | 16 | 4 | None | 20/20 | None | None |
| 4 (50) | 11 | >1,024 | 512 | 16 | 4 | None | 11/11 | None | None |
a
Nal, nalidixic acid; Flu, flumequine; Enr, enrofloxacin; Cip, ciprofloxacin.
b
AS-PCR-RFLP assay results.
c
HaeII digestion of the parC gene QRDR was performed for the most resistant isolates obtained after each treatment. ND, not done.