CHARACTERIZATION OF THE LANCEFIELD-GROUP-C STREPTOCOCCUS 16S-23S-RNA GENE INTERGENIC SPACER AND ITS POTENTIAL FOR IDENTIFICATION AND SUBSPECIFIC TYPING

The 16S-23S RNA gene intergenic spacers of isolates of Streptococcus e qui (n = 5), S. zooepidemicus (n = 5), S. equisimilis (n = 3) and S. d ysgalactiae (n = 2) were sequenced and compared. There were distinct r egions within the spacer, arranged in the order 1-9 for all S. equi an d one S. zooepidemicus isolate and 1,2 and 4-9 for the remaining isola tes. Region 4 was identical to the tRNA(ala) gene found in the 16S-23S intergenic spacers of other streptococci. Regions 1, 5, 6 and 7 had d istinct variations, each conserved in different isolates. However, amo ngst the intergenic spacers there were different combinations of varia nt regions, suggesting a role for DNA recombination in their evolution . The intergenic spacer of all isolates of S. equi and one S. zooepide micus isolate were almost identical. Primers derived from the variant sequences of regions 1 and 5 to 6 were used to group all S. zooepidemi cus (n = 17) and S. equi (n = 5) into 1 of 8 types by polymerase chain reaction; three S. zooepidemicus isolates typed the same as S. equi. S. equi and S. zooepidemicus were clearly distinguishable from S. equi similis and S. dysgalactiae which had shorter regions 5 and 6 and no r egion 7. Most homology for the group C sequences was found in previous ly published sequences for the 16S-23S intergenic spacers of S. angino sis, S. constellatus, S. intermedius, S. salivarius and S. agalactiae. A 75-90 nucleotide length shared with S. anginosus and S. intermedius in opposite orientations in the two main variants of region 6 support ed the role for DNA recombination in the evolution of the spacer. The 16S-23S intergenic spacers indicate that S. zooepidemicus was the arch etypal species for S. equi and that both are genetically more distant from S. equisimilis and S. dysgalactiae. The intergenic spacer can be used to identify specifically the group C streptococci and as an epide miological marker for S. zooepidemicus.