Abstract
.DELTA..psi.-reduced amiA mutants of Streptococcus pneumoniae were shown to be resistant to the positively charged antitumoral drugs 2-N-methylellipticinium (NME) and 2-N-methyl-9-hydroxyellipticinium (NMHE). Conversely, mutants selected for their resistance to NMHE were mapped within the amiA locus and exhibited the pleiotropic AmiA- phenotype. This shows that .DELTA..psi. is a critical parameter in determining resistance to these drgus in S. pneumoniae and suggests that they are accumulated within this bacterium in response to .DELTA..psi.. As a consequence NME and NMHE appear to be valuable tools for selecting .DELTA..psi.-reduced mutants in S. pneumoniae.