Determination of 16S ribosomal RNA gene copy number in Streptococcus uberis, S. agalactiae, S. dysgalactiae and S. parauberis.

Species-specific oligonucleotide probes and a universal oligonucleotide probe derived from sequences of 16S rRNA were hybridised to chromosomal DNA from Streptococcus agalactiae, S. dysgalactiae, S. parauberis and S. uberis following digestion with EcoRI. Due to the presence of a unique EcoRI site in each 16S rRNA gene, the number of hybridised fragments was indicative of the number of 16S rRNA genes. Southern hybridisation indicated six 16S rRNA genes in ten isolates of S. agalactiae, five genes in ten isolates of S. uberis, five genes in six isolates and six in another isolate of S. dysgalactiae, and six genes in four isolates of S. parauberis. For a fifth isolate of S. parauberis, six 16S rRNA genes were indicated by the universal probe but only five when hybridised to the species-specific probe, indicating sequence variation (microheterogeneity) within the probe target region.