TABLE 2.
Frequency of high-level resistance in colonies of transformants of clinical strains of low-level MRSA with the plasmid harboring a deletion in the rel-lytH region
| Bacterial strain | Parent/plasmid | MIC of methicillin (μg/ml) | Frequency of resistant coloniesa | Frequency of deletion in the chromosomal rel-lytH regionb (%) |
|---|---|---|---|---|
| SR17238 | 6.3 | 1.7 × 10−6 | ||
| SRM1664 | SR17238/pSR100 | 6.3 | 1.1 × 10−6 | |
| SRM1665 | SR17238/pSR108 | 25 | 1.3 × 10−3 | 100 |
| SR20118 | 12.5 | 6.6 × 10−8 | ||
| SRM2148 | SR20118/pSR108 | 12.5 | 5.5 × 10−6 | 100 |
| SR20137 | 12.5 | 5.6 × 10−7 | ||
| SRM2149 | SR20137/pSR108 | 25 | 3.8 × 10−5 | 100 |
| SR20202 | 25 | 5.4 × 10−6 | ||
| SRM2150 | SR20202/pSR108 | 50 | 1.3 × 10−4 | 100 |
| SR20280 | 6.3 | 2.6 × 10−6 | ||
| SRM2151 | SR20280/pSR108 | 6.3 | 7.8 × 10−6 | 58.3 |
a
Frequency of colonies grown on the agar plates containing 400 μg/ml methicillin, which was spread with the overnight culture in methicillin-free broth and incubated for 3 days at 37°C.
b
In 24 colonies of each transformant, for which their high-level resistance was confirmed by regrowth on agar plates containing 400 μg/ml of methicillin, deletion in the chromosomal rel-lytH region was investigated by the PCR method with primers 1 and 2 as described in Materials and Methods.