A technique permitting selection of penicillin-susceptible pneumococcal strains following transformation of a penicillin-resistant strain with a penicillin-susceptibility gene.

We report a technique useful for transformation experiments involving bacteria naturally competent for DNA transformation. It allows the selection of antibiotic-susceptible transformants following the transformation of a resistant strain with an antibiotic susceptibility gene. We show the effectiveness of this technique through the selection of penicillin-susceptible (MIC, 0.03 microg/ml) transformants following the transformation of a penicillin-resistant (MIC, 16 microg/ml) pneumococcal strain with a penicillin-susceptibility gene.