IS6770, an enterococcal insertion-like sequence useful for determining the clonal relationship of clinical enterococcal isolates.

Enterococci expressing resistance to antimicrobial agents are increasingly important nosocomial pathogens. Effective strategies to prevent or abort outbreaks of resistant enterococcal infection will rely on an accurate understanding of the mechanisms by which these organisms spread. A 1065-bp insertion-like sequence (IS6770) is present in varying copy numbers in > 90% of enterococcal strains thus far examined. Hybridization patterns resulting from hybridization of enterococcal genomic DNA with an internal IS6770 probe vary considerably between unrelated strains and correlate well with results of pulsed-field gel electrophoresis and field-inversion gel electrophoresis in identifying clonal relationships among enterococcal isolates. IS6770 analysis of several outbreaks of resistant enterococci has confirmed the spread of single resistant clones rather than the emergence of resistance within the resident flora. These results suggest that IS6770 hybridization will be a useful tool for tracing the epidemiology of nosocomial enterococcal infections.