Improved method for conjugative transfer by filter mating of Streptococcus pneumoniae

The frequency of conjugation during filter mating of pneumococcus was increased 10- to 100-fold when the filter was embedded in agar during incubation instead of being on the surface. The major effect was not due to protection from oxygen. The factor of increase was similar for transfer of plasmids and of chromosomal insertions of drug resistance elements.