title: Antibacterial effects of levofloxacin, erythromycin, and rifampin in a human monocyte system against Legionella pneumophila.
abstract: The antibacterial activities of levofloxacin, erythromycin, and rifampin against intracellular Legionella pneumophila L-1033, serogroup 1, were studied. In an in vitro system utilizing adherent human monocytes, L. pneumophila L-1033, a phagocytosis time period of 1 h, and antibiotic (levofloxacin, erythromycin, and/or rifampin) at 1 to 10 times the MIC, the CFU/ml values for the monocyte lysate were determined during 0- to 4-day time periods. The decrease in CFU/ml with levofloxacin at pH 7.4 was rapid, occurring within 24 h, and was drug concentration dependent (P < 0.01). The decrease in CFU with rifampin was first observed at 48 h (P < 0.01), while only a minimal decrease in CFU/ml was observed with erythromycin. Combination of levofloxacin and rifampin and of levofloxacin and erythromycin at ten times their MICs significantly decreased the CFU/ml value (P < 0.01), to the value attained by levofloxacin alone, while combination of rifampin and erythromycin did not. Removal of levofloxacin after 24 h of incubation resulted in regrowth of L. pneumophila L-1033, while a continued slow decrease in CFU/ml was seen following rifampin removal; CFU/ml values were unaffected by the removal of erythromycin. At 4 days, and even in assays performed following antibiotic removal, the CFU/ml value continued to be lower in the levofloxacin and rifampin assays than in the assays with erythromycin. Levofloxacin had a significantly higher bactericidal activity against L. pneumophila L-1033 than erythromycin or rifampin. In these assays, the addition of erythromycin or rifampin did not affect the antibacterial activity of levofloxacin.
authors.affiliation: Stratton Veterans Affairs Medical Center and Albany Medical College, Albany, New York, USA. baltch,aldona@albany.va.gov
authors.forename: A L
authors.initials: AL
authors.lastname: Baltch
authors.forename: R P
authors.initials: RP
authors.lastname: Smith
authors.forename: M A
authors.initials: MA
authors.lastname: Franke
authors.forename: P B
authors.initials: PB
authors.lastname: Michelsen
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D000890:Anti-Infective Agents / Q000494:pharmacology*; D000904:Antibiotics, Antitubercular / Q000494:pharmacology*; D015169:Colony Count, Microbial; D004359:Drug Therapy, Combination; D004917:Erythromycin / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D016952:Legionella pneumophila / Q000187:drug effects*; D064704:Levofloxacin; D009000:Monocytes / Q000187:drug effects / Q000382:microbiology; D015242:Ofloxacin / Q000494:pharmacology*; D012293:Rifampin / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D000890:Anti-Infective Agents; D000904:Antibiotics, Antitubercular; D004917:Erythromycin; D064704:Levofloxacin; D015242:Ofloxacin; D012293:Rifampin