title: High-level penicillin resistance and penicillin-gentamicin synergy in Enterococcus faecium.
abstract: Thirty-seven Enterococcus faecium strains with different levels of penicillin susceptibility were studied in time-kill experiments with a fixed concentration (5 micrograms/ml) of gentamicin combined with different penicillin concentrations (6 to 600 micrograms/ml). Synergy was defined as a relative decrease in counts of greater than 2 log10 CFU per milliliter after 24 h of incubation when the combination of the antibiotics was compared with its most active component alone. The minimal synergistic penicillin concentrations found were 6 micrograms/ml for 16 of 16 strains for which penicillin MICs were < or = 25 micrograms/ml, 20 to 100 micrograms/ml for 14 of 17 strains for which penicillin MICs were 50 to 200 micrograms/ml, and 200 to 500 micrograms/ml for 4 of 4 strains for which MICs penicillin were > 200 micrograms/ml. Penicillin-gentamicin synergy was observed even in high-level penicillin-resistant E. faecium strains at penicillin concentrations close to one-half the penicillin MIC. The possibility of treating infections caused by high-level penicillin-resistant E. faecium strains with penicillin-gentamicin combinations in particular cases may depend on the penicillin levels attainable in vivo.
authors.affiliation: Area de Bioquímica y Biología Molecular, Universidad de la Rioja, Madrid, Spain.
authors.forename: C
authors.initials: C
authors.lastname: Torres
authors.forename: C
authors.initials: C
authors.lastname: Tenorio
authors.forename: M
authors.initials: M
authors.lastname: Lantero
authors.forename: M J
authors.initials: MJ
authors.lastname: Gastañares
authors.forename: F
authors.initials: F
authors.lastname: Baquero
mesh_terms: D004357:Drug Synergism; D016984:Enterococcus faecium / Q000187:drug effects*; D005839:Gentamicins / Q000494:pharmacology*; D016908:Gram-Positive Bacterial Infections / Q000382:microbiology; D008826:Microbial Sensitivity Tests; D010403:Penicillin Resistance; D010406:Penicillins / Q000494:pharmacology*
chemical_list: D005839:Gentamicins; D010406:Penicillins