Physical and genetic map of Streptococcus mutans GS-5 and localization of five rRNA operons.

The physical map of the 2.1 megabase chromosome of Streptococcus mutans GS-5 has been refined by including all ApaI and SmaI fragments of 5 kbp or greater, and by positioning the fragments generated by the endonuclease I-CeuI. Sixty-three new genetic loci have been added to the map, so that it now contains 90 loci. The new loci include those for 35 cloned streptococcal genes of established function and for 23 S. mutans genes of putative function. In addition, five rrn operons were identified and placed on the map of the chromosome. The presence of a SmaI site in each of the rrn operons allowed the direction of transcription of each operon to be deduced. The orientation of the rrn loci indicates that their transcription is directed away from a small region of the chromosome, identifying a possible region for the initiation of chromosome replication.

Molecular epidemiology by ribotyping and PCR-ribotyping of Enterococcus faecium strains isolated from intercontinental areas.

In this study classical ribotyping based on hybridization of an enteroccocal ribosomal operon previously cloned from Enterococcus hirae (Sechi and Daneo-Moore, 1993) with XbaI cut chromosomal DNA and PCR-ribotyping were used to characterize the molecular epidemiology of 131 Enterococcus faecium, with high-level resistance to gentamicin, isolated from different hospitals in Italy and the United States. The ribotyping was able to differentiate all 131 clinical isolates into 96 family patterns. These family patterns appeared to be useful in establishing epidemiological spread. The results obtained were in agreement with those previously published, suggesting the presence of five to six operons in the Enterococcus genus (Sechi et al., 1994). We performed PCR-ribotyping, based on conserved sequences at the 3' end of the enterococcal 16S rrn and the 5' end of the 23S rrn, on 131 clinical isolates as well as on several enterococcal ATCC strains tested. The results were then compared with those obtained with the classical ribotyping method. The results suggest the presence of at least four classes of intergenic spacers among enterococci, but these classes are not helpful in differentiating between Enterococci or among Enterococcal isolates.