High-level resistance to gentamicin in clinical isolates of Streptococcus (Enterococcus) faecium

Abstract

During a 14-month period beginning in July 1986, three distinct clinical isolates of Streptococcus (Enterococcus) faecium demonstrating high-level resistance (MIC, greater than 2,000 micrograms/ml) to gentamicin, kanamycin, tobramycin, and streptomycin were recovered from individual patients at one institution. Combinations of ampicillin with any of these agents failed to show bactericidal synergism. By filter-mating techniques, high-level gentamicin resistance could be transferred into a susceptible recipient of the same species at frequencies as high as 1 x 10(-4); transfer into Streptococcus faecalis JH2-7 occurred at lower frequencies (less than 2 x 10(-7). Aminoglycoside substrate profile analysis of clinical isolates as well as of laboratory-derived cured strains and transconjugants revealed 2"-aminoglycoside phosphotransferase and 3'-aminoglycoside phosphotransferase (III) phosphorylating enzymes, AAC-6' acetylating activity above that attributable to the intrinsic activity characteristic of S. faecium, and a streptomycin adenylylating enzyme. All three isolates carried a 51-megadalton plasmid. Curing of this plasmid or conjugative transfer into susceptible recipients was associated with the loss or acquisition of high-level gentamicin resistance, respectively. Loss of high-level gentamicin resistance was also observed when curing techniques resulted in a decrease in the size of this plasmid equivalent to a 10-megadalton deletion. Transferable, high-level resistance to gentamicin and other aminoglycosides, which was previously recognized in S. faecalis, has now emerged in clinical isolates of S. faecium, with the attendant concerns for possible spread.

Transferability and genetic relatedness of high-level gentamicin resistance among enterococci

“…Intraspecies transfer of gentamicin resistance has been reported for E. faecalis and E. faecium, as has interspecies transfer between these two organisms (3,5,8,12,19). Results from the present experiments demonstrate the capacity for the intra-and interspecies transfer of high-level gentamicin resistance in two additional enterococcal species, E. avium and E. gallinarum.…”

“…Recently, HodelChristian and Murray (7) have reported the genetic determinant in E. faecalis to be on a mobile element, Tn5281. Although gentamicin resistance in E. faecalis has been well characterized, the same cannot be said of resistance in other enterococcal species (3,5,8,13,14). In the present study, we used clinical isolates to investigate the transfer of this resistance among various enterococcal species and we also determined the genetic relatedness between gentamicin resistance in E. faecalis and that in other species.…”

Construction of Improved Temperature-Sensitive and Mobilizable Vectors and Their Use for Constructing Mutations in the Adhesin-Encoding acm Gene of Poorly Transformable Clinical Enterococcus faecium Strains

“…Similar transformation efficiencies were noted for pAT18 (with the pAM␤1 replicon) with this strain. Two other strains that were found to be moderately transformable were D344-S (a laboratory recipient isolate and spontaneous mutant of D344 [48]) and an American Type Culture Collection (ATCC 51558) recipient isolate, GE-1 (10). Their efficiencies of transformation were 100-fold less than that of pAM401 transformation into E. faecalis OG1X (64).…”

Chromosomally mediated beta-lactamase production and gentamicin resistance in Enterococcus faecalis

“…CH 19, isolated from a wound culture, was the original isolate which appeared to spread throughout the ward. CX 19 was a P-lactamase-producing transcipient derived from the mating of CH 19 with JH2-7, a rifampin-resistant, fusidic acid-resistant, Thy-strain of E. faecalis (5). CH 116 was a urine isolate obtained from a patient on a separate hospital ward who had a temporally distant exposure to the ward with the outbreak.…”