Intracellular activity of ABT-773 and other antimicrobial agents against Legionella pneumophila

The intracellular activity of ABT-773 against Legionella pneumophila was compared with azithromycin and ciprofloxacin using HL-60 cells. Against L. pneumophila ATCC 33152 and three clinical isolates the MICs (mg/L) were ABT-773 0.015, ciprofloxacin 0.03 and azithromycin 0.03. At 48 h, the mean percentage inhibition was as follows: 28.5 +/- 5.9% and 32.6 +/- 4.6% at 8 x and 16 x MIC of ABT-773; 38.1 +/- 8.6% and 48.2 +/- 7.0% at 8 x and 16 x MIC of ciprofloxacin; and 26.3 +/- 9.9% and 28.5 +/- 9.9% at 8 x and 16 x MIC of azithromycin. In this study, all three agents were highly active, with ABT-773 demonstrating similar activity to azithromycin against L. pneumophila.