STRUCTURAL ORGANIZATION OF THE STREPTOCOCCUS-PNEUMONIAE CHROMOSOME AND RELATEDNESS OF PENICILLIN-SENSITIVE AND PENICILLIN-RESISTANT STRAINSIN TYPE 9V

Fragmentation of Streptococcus pneumoniae genomic DNA with low-frequen cy-cleavage restriction endonucleases and separation of the fragments by field-inversion gel electrophoresis (FIGE) provides a DNA-fingerpri nt of a strain. This method enables us to construct a physical and gen etic map of the R6 laboratory strain what will be presented. The origi n of replication containing several Dna boxes was located in the dnaA region. It was of interest to compare the profiles of subclones. Two c lones of strain R36A (R6 and C13) were cultivated separately for more than 15,000 generations in two laboratories. FIGE profiles differed by only one band. Another R36A descendant, isolated in 1958 by Ravin, st rain Rx was of interest since it was deficient in Dpn restriction enzy mes and methylases and in the hex B function. Its origin was questiona ble; its profile is identical to others R6 descendants, demonstrating that Rx is derived from R36A. FIGE analysis was carried out on several penicillin-resistant strains of type 9V because penicillin-resistance in this type increased recently. The profiles of a collection of a nu mber of these resistant isolates were very similar, showing that they result from a clone. The profiles of penicllin sensitive isolates of t he same type are very similar to the resistant isolates. This suggests that the 9V type has spread recently from a clone, and the resistance genes have mutated and were selected when penicillin was extensively used.