Plasmid-mediated resistance to aminocyclitol antibiotics in group D streptococci

Abstract

Streptococcus faecalis BM4100 was resistant to high levels of gentamicin, kanamycin and structurally related antibiotics. The genes conferring resistance to aminocyclitols in this strain were carried by a plasmid, pIP800, self-transferable to other S. faecalis strains. The aminocyclitol resistance was mediated by constitutively synthesized phosphotransferase and acetyltransferase activities. It was inferred that phosphorylation occurred at the 2"-hydroxyl group and that acetylation occurred at the 6''-hydroxyl group of the aminocyclitols. The enzyme activities were not separable by gel filtration or by isoelectric focusing. Their apparent MW was 31,000, and their isoelectric point was 5.3. With respect to substrate profile, size and charge, the transferases from strain BM4100 resembled closely those with identical site specificity described in staphylococci. Plasmid gene transfer may occur between the 2 pathogenic bacterial genera.