Table 1.
Measurement of drug resistance of E. coli expressing A. baumannii MacA-MacB-TolC or transport inactive mutants
| Component(s) expressed | MIC (μg ml−1) | |||||||
|---|---|---|---|---|---|---|---|---|
| Macrolide (MacB substrates) | AcrB substrates | |||||||
| EM | CAM | RXM | AZM | SPM | LM | ACR | SDS | |
| None (empty vector) | 1.56 | 1.56 | 4.41 | 0.55 | 4.41 | 2.2 | 4.41 | 50.0 |
| MacA-MacB(E172Q)-TolC | 1.10 | 1.56 | 1.56 | 0.39 | 4.41 | 1.10 | 4.41 | 50.0 |
| MacA-MacB-TolC | 2.21 | 2.21 | 6.25 | 0.55 | 6.25 | 3.13 | 4.41 | 50.0 |
| MacA-MacB | 1.56 | 2.21 | 1.56 | 0.28 | 4.41 | 1.10 | 4.41 | 50.0 |
| MacA-TolC | 1.10 | 1.56 | 1.56 | 0.28 | 2.21 | 1.10 | 4.41 | 50.0 |
| MacB-TolC | 1.56 | 1.56 | 1.56 | 0.28 | 4.41 | 1.10 | 4.41 | 50.0 |
| MacA-MacB(ΔC10)-TolC | 0.78 | 1.10 | 1.56 | 0.28 | 2.21 | 1.10 | 4.41 | 50.0 |
EM, erythromycin; CAM, clarithromycin; RXM, roxithromycin; AZM, azithromycin; SPM, spiramycin; LM, leucomycin; ACR, acriflavine; SDS, sodium dodecyl sulfate
The resistance levels are shown as minimum inhibitory concentration (MIC) in µg ml−1determined by the agar dilution method. Values are based on data shown in Fig. 1. Cells expressing the inactive Walker B E172Q MacB mutant were used as a negative control rather than non-expressing cells that lack the expression of foreign protein. Drug resistance is restored by expression of the functional MacA-MacB-TolC tripartite complex. AcrB substrates acriflavine and SDS are not transported by MacA-MacB-TolC. The MacB mutant lacking the carboxy-terminal coupling helix, CH2 is abbreviated as MacB(ΔC10)