Pulsed-f ield gel electrophoresis of the genomic DNA of penicillin-resistant strains of Streptococcus pneumoniae was carried out. Eleven clinical strains of serogroup 9 from different French towns and Paris hospitals were tested. The restriction enzymes Apal and SmaI were used to digest intact chromosomes, and the fragments were resolved by f ield-inversion gel electrophoresis (FIGE). Five strains were similar using Apal and Smal. Four others were closely related when using Apal, and five others were closely related when using Smal. These results suggest that 10 of these strains are genetically related and have a clonal origin. The profile of the eleventh strain was completely different. Thus, in a given serotype the spreading of penicillin resistance can result from both clonal and independent events. Five strains had similar FIGE profiles to strains first isolated in Spain, suggesting that a resistant strain had spread from Spain to France.

The Escherichia coli-Brevibacterium Zactofermentum shuttle vector pBLA was introduced into intact cells of B. lactofermenturn by electrotransformation. Several parameters of this procedure such as voltage and cell concentration were analysed. Optimal conditions gave an efficiency of lo6 transformants per pg of DNA. Two recalcitrant strains could be electrotransformed when an ampicillin pretreatment step was used. Electrotransformation experiments using DNAase or different structural forms of plasmid DNA showed that the electrotransformation process is quite different from natural transformation involving competence development. Restriction-modification-proficient B. lactofermentum could be efficiently electrotransformed with pBLA DNA isolated from E. coli. This restriction-modification system therefore seems to be overcome by electrotransformation. Thus electrotransformation may efficiently replace the protoplast bacterial transformation method.

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