Copyright X 1993, American Society for Microbiology Characterization of the Chromosomal aac(6')-Ii Gene Specific for Enterococcus faecium

Chromosomal gene aac(6')-Ii of Enterococcus faecium CIP 54-32, encoding a 6'-N-aminoglycoside acetyl-transferase was characterized. The gene was identified as a coding sequence of 549 bp corresponding to a protein with a calculated mass of 20,666 Da. Analysis of the sequence of the deduced protein suggested that it was the second member of a subfamily of AAC(6')-I enzymes. Insertional inactivation of aac(6')-Ii led to aminoglycoside susceptibility of CIP 54-32, suggesting that this gene plays a role in resistance to AAC(6')-I substrates. The gene was detected by DNA hybridization in all 26 strains ofE.faecium tested but not in 44 other enterococci of 13 species. These data suggest that the aac(6')-Ii gene is species specific and may be used to identify E. faecium. The bacterial genus Enterococcus includes a minimum of 14 species (19). Enterococcusfaecalis and E. faecium are the most common species causing human disease and represent, respectively, 87 and 9 % of clinical enterococcal isolates (24). Some strains of the remaining species are occasionally isolated from humans but are more commonly isolated from plants and animals. Enterococci are increasingly responsibl