Table 1.
Characteristics of macrolide resistance genes in Campylobacter jejuni strains showing varied resistance to azithromycin and erythromycina.
| Strain | Source | MIC (μg/mL) | cmeB c | ermB c | Mutations | L22 insertions |
|||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Azithromycin | Erythromycin | 23S rRNA |
L4 | L22 | |||||||||
| -EPI | +EPI | Foldb | -EPI | +EPI | Foldb | ||||||||
| 33560 | ATCC | 0.25 | 0.06 | 4 | 1 | 0.25 | 4 | nt | nt | wt | wt | wt | wt |
| A16-CF-329-3 | CM | 4 | 0.5 | 8 | 0.5 | 0.5 | 1 | + | - | wt | V196A | A103V, S109A | wt |
| CM13-HL-010-1 | CM | 4 | 0.125 | 32 | 8 | 0.25 | 32 | + | - | wt | V80I, V196A | A103V, S109A, V137A | wt |
| CM13-HL-012-1 | CM | 4 | 0.5 | 8 | 8 | 0.125 | 64 | + | - | wt | V80I, V196A | A103V, S109A, V137A | wt |
| CM13-MWC-BS-004 | CM | 8 | 0.125 | 64 | 0.5 | 0.025 | 20 | + | - | wt | V196A | A103V, S109A, V137A | wt |
| A16-CF-127-1-S1 | BC | 8 | 0.25 | 32 | 1 | 0.25 | 4 | + | - | wt | wt | wt | wt |
| A16-CF-318-3 | CM | 8 | 0.25 | 32 | 1 | 0.015 | 67 | + | - | wt | V121A, T177S, M192I, V196A | V137S | 114VAKKAP115 |
| DM13-MP-WS-002 | DM | 8 | 0.5 | 16 | 64 | 0.25 | 256 | + | - | wt | V196A | A103V, S109A, V137A | wt |
| CM13-OP-004-1 | CM | 8 | 0.25 | 32 | 64 | 0.5 | 128 | + | - | wt | wt | wt | wt |
| A16-CF-129-1-S1 | CM | 8 | 0.125 | 64 | 128 | 0.5 | 256 | + | - | wt | wt | wt | wt |
| CM13-HL-BS-021 | CM | 16 | 1 | 16 | 32 | 2 | 16 | + | - | wt | V196A | wt | wt |
| DM13-JDW-WL-007 | DM | 16 | 0.25 | 64 | 64 | 0.5 | 128 | - | - | wt | V196A | V137A | 114VAKKAP115 |
| DM13-JDW-WL-009 | DM | 16 | 16 | 1 | 64 | 64 | 1 | + | - | wt | V121A, T177S, M192I, V196A | S109A, V137A | 114VAKKAP115 |
| CM13-MWC-WL-008 | CM | 16 | 1 | 16 | 64 | 1 | 64 | + | - | wt | V196A | A103V, S109A, V137A | wt |
| CM13-DW-BL-005 | CM | 16 | 1 | 16 | 64 | 1 | 64 | + | - | wt | V196A | I65V, A103V, S109A, V137A | wt |
| DM13-JW-SS-017 | DM | 32 | 0.5 | 64 | 64 | 0.5 | 128 | + | - | wt | V121A, V196A | I65V, A103V, S109A, V137A | wt |
a. Abbreviations: ATCC, American Type Culture Collection; CM, chicken meat; BC, breeder chicken; DM, duck meat; EPI: efflux pump inhibitor; nt: not test; A: Ala; I: Ile; K: Lys; M: Met; P: Pro; S: Ser; V: Val; T: Thr; wt: wild type.
b. Fold values were calculated as MIC without EPI/MIC with EPI.
c. +/-, indicates whether or not the target genes were detected.
The MIC breakpoints for azithromycin: susceptible, ≤ 2 μg/mL; intermediate, 4 μg/mL; and resistant, ≥ 8 μg/mL; for erythromycin: susceptible, ≤ 8 μg/mL; intermediate, 16 μg/mL; and resistant, ≥ 32 μg/mL.