title: Bactericidal activities of antibiotics against vancomycin-resistant Enterococcus faecium blood isolates and synergistic activities of combinations.
abstract: The effects of teicoplanin (8 micrograms/ml), ampicillin (64 micrograms/ml), imipenem (32 micrograms/ml), and gentamicin (4 micrograms/ml), alone and in combination, against 13 unique blood isolates of vancomycin-resistance (MIC for 90% of isolates tested [MIC90], 512 micrograms/ml), teicoplanin-susceptible (MIC90, 2.0 micrograms/ml), ampicillin-resistant (MIC90, 128 micrograms/ml), and non-beta-lactamase-producing Enterococcus facium (vancomycin-resistant enterococci [VRE] isolates) were evaluated by time-kill studies. All 13 isolates exhibited high-level resistance to streptomycin; 7 isolates exhibited high-level gentamicin resistance (HLGR). After 24 h of incubation, ampicillin (64 micrograms/ml) combined with gentamicin (4 micrograms/ml) was bactericidal against three of the VRE isolates that did not display HLGR. Synergy between ampicillin and gentamicin was not observed against these isolates. Teicoplanin (8 micrograms/ml) alone was bactericidal at 24 h against five of six VRE isolates that lacked HLGR, but was not bactericidal against any HLGR VRE isolate at that time point. The addition of ampicillin (64 micrograms/ml) or imipenem (32 micrograms/ml) to teicoplanin did not significantly enhance the killing of HLGR VRE isolates as a group (P = 0.335). However, there was a trend toward improved killing of some HLGR VRE isolates by teicoplanin plus imipenem. Vancomycin (32 micrograms/ml) combined with ampicillin (64 micrograms/ml) was neither bactericidal nor synergistic against HLGR VRE isolates. Overall, bactericidal activity was attainable against 7 of 13 VRE isolates at 24 h.
authors.affiliation: Department of Medicine, Rush-Presbyterian-St. Luke's Medical Center, Chicago, Illinois 60612.
authors.forename: M K
authors.initials: MK
authors.lastname: Hayden
authors.forename: G I
authors.initials: GI
authors.lastname: Koenig
authors.forename: G M
authors.initials: GM
authors.lastname: Trenholme
mesh_terms: D000667:Ampicillin / Q000494:pharmacology; D016470:Bacteremia / Q000382:microbiology*; D004352:Drug Resistance, Microbial; D004357:Drug Synergism; D004359:Drug Therapy, Combination / Q000494:pharmacology*; D016984:Enterococcus faecium / Q000187:drug effects*; D005839:Gentamicins / Q000494:pharmacology; D006801:Humans; D017334:Teicoplanin / Q000494:pharmacology; D014640:Vancomycin / Q000494:pharmacology*
chemical_list: D005839:Gentamicins; D017334:Teicoplanin; D014640:Vancomycin; D000667:Ampicillin