Characterization of Streptococcus criceti insertion sequence ISScr1.

A novel insertion sequence element of the IS982 family, ISScr1, was previously identified in Streptococcus criceti strain E49 as a disrupted paaB gene encoding an antigen I/II homologous protein. In this study, we identified two divergent inserted regions of ISScr1 in S. criceti E49 by inverse polymerase chain reaction, the gene-walking method, and screening of the partial plasmid library. Nucleotide sequence analysis indicated the possible explanation that transposition generated 8- and 9-bp direct repeat sequences. DNA hybridization analysis revealed that an identical hybridization pattern to ISScr1 was observed in the four S. criceti strains studied and that at least three copies of ISScr1 were preserved in S. criceti strains. In addition, we found different susceptibility to erythromycin and diverse agglutination properties induced by dextran in S. criceti. Furthermore, DNA hybridization analysis showed that no ISScr1-like copy was detected in the other 14 strains of oral streptococci tested.