EMERGENCE OF VANCOMYCIN RESISTANCE IN THE GENUS STREPTOCOCCUS - CHARACTERIZATION OF A VANB TRANSFERABLE DETERMINANT IN STREPTOCOCCUS-BOVIS

Streptococcus bovis NEM760 was isolated from a stool swab collected on admission from a patient as surveillance for vancomycin-resistant ent erococci, Strain NEM760 was identified as S. bovis by conventional bio chemical methods and partial sequence analysis of its 16S rRNA. This s train was resistant to a low level of vancomycin (MIC, 64 mu g/ml) but was susceptible to teicoplanin (MIC, 1 mu g/ml), and vancomycin induc ed resistance to both glycopeptides. The presence of a vanB-related ge ne in NEM760 was demonstrated in a PCR assay which enabled specific am plification of a 635-bp internal segment of vanB. Sequence analysis of the corresponding PCR product revealed that it was highly homologous (96% identity) to the prototype vanB sequence of Enterococcus faecalis V583, The VanB resistance determinant of S. bovis NEM760 was transfer red by conjugation to E. faecalis and Enterococcus faecium at a simila r frequency of 2 x 10(-5) per donor. SmaI-digested genomic DNAs of ind ependently obtained transconjugants of E. faecalis and E. faecium were analyzed by pulsed-field gel electrophoresis and Southern hybridizati on with a vanB DNA probe, The electrophoretic and hybridization patter ns obtained with all transconjugants of the same species were indistin guishable and revealed vanB-containing chromosomal insertions of appro ximately 100 kb, These results suggest that the genes mediating VanB-t ype resistance in S. bovis NEM760 are part of large transferable genet ic elements, The results presented in the report demonstrate for the f irst time the role of streptococci in the dissemination of vancomycin resistance among gram-positive bacteria.