title: Synergistic post-antibiotic effect of amikacin and beta-lactam antibiotics on Enterococcus faecalis.
abstract: The in-vitro post-antibiotic effect (PAE) of amikacin alone and in combination with ceftazidime, ceftriaxone and piperacillin was studied for two strains of Enterococcus faecalis using a bioluminescent assay of bacterial ATP. The two strains of E. faecalis were resistant to amikacin, ceftazidime and ceftriaxone but sensitive to piperacillin. The bacterial cultures were incubated with the beta-lactam antibiotics for 1 h and concentrations of amikacin between 2-64 mg/l were then added. Thereafter, incubation continued with the combinations for one more hour. After dilution, regrowth was monitored by measuring bacterial ATP every hour. Increasing concentrations of amikacin (2-64 mg/l), ceftazidime (8-32 mg/l) and ceftriaxone (32-128 mg/l) resulted in little or no PAE (0-0.3 h) on these strains. PAEs of 0.5 to 1.6 h resulted from exposure to piperacillin (4-32 mg/l). In combination amikacin and piperacillin increased the PAE to 5.5 h. A synergistic PAE was also seen when the enterococci were exposed to amikacin combined with ceftazidime or ceftriaxone in concentrations close to the MICs of the latter antibiotics.
authors.affiliation: Department of Infectious Diseases, University Hospital, Linköping, Sweden.
authors.forename: B
authors.initials: B
authors.lastname: Isaksson
authors.forename: H
authors.initials: H
authors.lastname: Hanberger
authors.forename: R
authors.initials: R
authors.lastname: Maller
authors.forename: L E
authors.initials: LE
authors.lastname: Nilsson
authors.forename: M
authors.initials: M
authors.lastname: Nilsson
mesh_terms: D000583:Amikacin / Q000494:pharmacology*; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002442:Ceftazidime / Q000494:pharmacology; D002443:Ceftriaxone / Q000494:pharmacology; D004357:Drug Synergism; D004359:Drug Therapy, Combination / Q000494:pharmacology; D004697:Endocarditis, Bacterial / Q000382:microbiology; D013293:Enterococcus faecalis / Q000187:drug effects*; D006801:Humans; D008826:Microbial Sensitivity Tests; D010878:Piperacillin / Q000494:pharmacology; D013290:Streptococcal Infections / Q000382:microbiology
chemical_list: D000900:Anti-Bacterial Agents; D002443:Ceftriaxone; D000583:Amikacin; D002442:Ceftazidime; D010878:Piperacillin