TABLE 3.
Different mgrB lesions detected in the colistin-resistant strains and results of complementation experiments with strains representative of each type of lesiona
| Strain | mgrB lesionb | Colistin MIC (μg/ml) | Colistin MIC after complementation (μg/ml)c | pmrK expression (mean ± SD) | pmrK expression after complementation (mean ± SD) | phoQ expression (mean ± SD) | phoQ expression after complementation (mean ± SD) |
|---|---|---|---|---|---|---|---|
| KKBO-1 | WT | 0.125 | 0.064 | 1 | 1.24 ± 0.51 | 1 | 0.93 ± 0.18 |
| KP207-2 | Insertional inactivation, IS5-like element at nt 75 (RW) | 16 | 0.5 | 6.19 ± 0.19 | 1.34 ± 0.13 | 3.56 ± 0.15 | 0.92 ± 0.17 |
| KP04C62 | Insertional inactivation, IS5-like element at nt 126 (FW) | 32 | 0.03 | 7.97 ± 0.12 | 1.81 ± 0.11 | 4.42 ± 0.25 | 1.46 ± 0.35 |
| KP23C12 | Insertional inactivation, IS1F-like element at nt 105 (FW) | 32 | 0.25 | 8.54 ± 0.09 | 2.04 ± 0.23 | 8.81 ± 0.44 | 1.11 ± 0.14 |
| KPIAC | t71a (L24H) | 32 | 0.03 | 3.25 ± 0.23 | 1.87 ± 0.37 | 2.98 ± 0.77 | 1.24 ± 0.26 |
| KP04C83 | Δ18/27 (frameshift and premature termination) | 32 | 0.03 | 5.15 ± 0.04 | 1.59 ± 0.34 | 7.23 ± 0.30 | 2.18 ± 0.45 |
| KP06C01 | g109a (G37S) | 16 | 0.03 | 6.61 ± 0.07 | 1.97 ± 0.14 | 6.65 ± 0.21 | 0.48 ± 0.34 |
| KP08C16 | a7t (nonsense, premature termination) | 32 | 0.03 | 5.44 ± 0.11 | 1.82 ± 0.22 | 4.22 ± 0.29 | 2.18 ± 0.33 |
| KP10C06 | Δg47 (frameshift and premature termination) | 32 | 0.03 | 10.39 ± 1.12 | 1.10 ± 0.04 | 11.45 ± 1.23 | 1.08 ± 0.45 |
| KP4707 | g83a (C28Y) | 32 | 0.03 | 9.51 ± 0.32 | 1.48 ± 0.20 | 14.02 ± 1.17 | 3.71 ± 0.75 |
| KP12C48 | Δ109/119 (frameshift and premature termination) | 32 | 0.03 | 5.37 ± 0.15 | 1.69 ± 0.17 | 9.61 ± 0.55 | 1.59 ± 0.15 |
| KP4553 | Insertional inactivation, ISKpn14 at nt 124 (FW) | 16 | 0.12 | 5.97 ± 0.18 | 1.99 ± 0.18 | 4.72 ± 0.35 | 1.20 ± 0.39 |
| KPTRAV | ΔmgrB (from −400 to +599) | 16 | 0.06 | 7.86 ± 0.87 | 2.08 ± 0.34 | 4.08 ± 0.23 | 0.97 ± 0.11 |
| KPKL52MG11 | ΔmgrB locus | 8 | 0.12 | 3.26 ± 0.07 | 0.78 ± 0.24 | 7.54 ± 0.54 | 1.75 ± 0.65 |
| KP4603 | ΔmgrB locus | 64 | 0.12 | 4.21 ± 0.13 | 1.77 ± 0.13 | 5.05 ± 0.05 | 1.02 ± 0.34 |
| KP4623 | ΔmgrB locus | 64 | 0.12 | 5.75 ± 0.52 | 1.08 ± 0.36 | 4.51 ± 0.39 | 0.77 ± 0.43 |
a
The expression levels of pmrK and phoQ genes (presented as fold increase) were normalized against the value obtained with the colistin-susceptible strain KKBO-1 (10).
b
WT, wild type; for explanation of the nature of mgrB lesions, see Table 1.
c
MIC testing of the complemented strains was performed in medium supplemented with 40 μg/ml of tetracycline, to avoid plasmid loss.