title: Comparative study of the bactericidal activity of ampicillin/sulbactam and erythromycin against intracellular Legionella pneumophila.
abstract: Intracellular bactericidal activity of ampicillin/sulbactam and erythromycin was determined with a human macrophage-like (U-937) cell line infected with Legionella pneumophila. Cell monolayers inoculated with L. pneumophila were treated with erythromycin, ampicillin, sulbactam, or ampicillin/sulbactam during the logarithmic phase of bacterial growth. Intracellular bacterial counts were determined at 2-h intervals for 8 h from the time that antibiotics were added. The number of viable intracellular bacteria increased during this time by 0.9 x log10 cfu/mL (P < 0.05) in the control culture, did not change significantly in the cultures treated with ampicillin or sulbactam, decreased by 0.8 x log10 cfu/mL (P < 0.05) with erythromycin, and decreased by 1.8 x log10 cfu/mL with ampicillin/sulbactam (P < 0.05). The number of cfu/mL was significantly less after incubation with ampicillin/sulbactam than with erythromycin (P < 0.05). Ampicillin/sulbactam appeared to have greater bactericidal activity against intracellular L. pneumophila than erythromycin in this in-vitro model. The bactericidal action of ampicillin/sulbactam was significantly greater than would be expected from the additive effects of ampicillin plus sulbactam, suggesting synergic bactericidal activity.
authors.affiliation: Louisville Veterans Affairs Medical Center, Kentucky.
authors.forename: J A
authors.initials: JA
authors.lastname: Ramirez
authors.forename: J T
authors.initials: JT
authors.lastname: Summersgill
authors.forename: R D
authors.initials: RD
authors.lastname: Miller
authors.forename: T L
authors.initials: TL
authors.lastname: Meyers
authors.forename: M J
authors.initials: MJ
authors.lastname: Raff
mesh_terms: D000667:Ampicillin / Q000494:pharmacology*; D002460:Cell Line; D015169:Colony Count, Microbial; D004359:Drug Therapy, Combination / Q000494:pharmacology; D004917:Erythromycin / Q000494:pharmacology*; D006801:Humans; D016952:Legionella pneumophila / Q000187:drug effects* / Q000254:growth & development; D008264:Macrophages / Q000382:microbiology; D008826:Microbial Sensitivity Tests; D013407:Sulbactam / Q000494:pharmacology*
chemical_list: D004917:Erythromycin; C035444:sultamicillin; D000667:Ampicillin; D013407:Sulbactam