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Antimicrobial Agents and Chemotherapy, December 1998, p. 3153-3156, Vol. 42, No. 12
0066-4804/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Antibacterial Effects of Levofloxacin, Erythromycin, and Rifampin in a Human Monocyte System against Legionella pneumophila

Aldona L. Baltch,* Raymond P. Smith, Mary A. Franke, and Phyllis B. Michelsen

Stratton Veterans Affairs Medical Center and Albany Medical College, Albany, New York

Received 10 September 1997/Returned for modification 27 May 1998/Accepted 17 September 1998

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.

* Corresponding author. Mailing address: Infectious Diseases (111D), Stratton VA Medical Center, 113 Holland Ave., Albany, NY 12208. Phone: (518) 462-3311, ext. 3080. Fax: (518) 462-3350. E-mail: baltch,aldona{at}albany.va.gov.

Antimicrobial Agents and Chemotherapy, December 1998, p. 3153-3156, Vol. 42, No. 12
0066-4804/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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