TABLE 1.
Susceptibility to AMK and KAN of E. coli XL1-Blue strains
| Substitutiona | MIC (μg/ml)b
|
Susceptibility phenotypec | |
|---|---|---|---|
| AMK | KAN | ||
| None | 0.25 | 0.25 | |
| pJHCMW1 (wild type) | 32 | 192 | |
| P155A | 12 | 48 | I2 |
| S156A | 32 | 192 | R |
| P157A | 6 | 24 | I2 |
| S158A | 96 | 256 | R |
| N159A | 0.75 | 32 | I1 |
| L160A | 16 | 48 | I2 |
| R161A | 24 | 128 | R |
| I163A | 2 | 24 | I2 |
| R164A | 12 | 128 | R |
| C165A | 16 | 64 | R |
| Y166A | 1.5 | 256 | Specificity |
| E167A | 2 | 4 | S |
| K168A | 6 | 16 | I2 |
| G170A | 6 | 96 | I1 |
| F171A | 1 | 1.5 | S |
| E172A | 32 | 96 | R |
| R173A | 16 | 128 | R |
| Q174A | 32 | 128 | R |
| G175A | 32 | 128 | R |
All mutations were performed with pJHCMW1, and the plasmid was introduced by transformation into E. coli XL1-Blue.
MICs were determined by the E-test.
For the purpose of the comparisons in this paper, the susceptibility phenotypes of the mutants were divided into the following four groups: R, resistant (MICs not more than threefold lower than that for the wild type); I, intermediate levels of resistance; S, susceptible (the MICs of both antibiotics were lower than 6 μg/ml; and Specificity, the MIC of one antibiotic (AMK) was at the susceptible level and the MIC of the other (KAM) was at the resistance level. The I group was subdivided into two groups on the basis of the resistance profile conferred by these derivatives: I1, resistance related to that of Y166A (Specificity) but not as pronounced; I2, the MICs of both antibiotics between those for the R and S groups.