Comparative in vitro bacteriostatic and bactericidal activity of trovafloxacin, levofloxacin and moxifloxacin against clinical and environmental isolates of Legionella spp.

The susceptibility of 140 Legionella spp isolates (106 clinical and 34 environmental isolates) to trovafloxacin (TRFX), levofloxacin (LEVX), moxifloxacin (MOFX), ciprofloxacin (CIPX), ofloxacin (OFLX), erythromycin (ERY), azithromycin (AZI) and rifampicin (RIF) was studied using a standard microdilution method and buffered yeast extract broth (BYE) supplemented with 0.1% alpha-ketoglutarate. The post-antibiotic effects (PAEs) of the study drugs against 10 clinical isolates of Legionella pneumophila sg.1 were compared. The MIC inhibiting 90% of strains tested on BYEalpha broth were 0.008, 0.016, 0.016, 0.06, 0.125, 0.5, 0.5, and 0.004 mg/l for TRFX, LEVX, MOXX, CIP, OFLX, ERY, AZI, and RIF, respectively. The MBC/MIC ratios ranged from one to eight depending on the antibiotic tested: TRFX [1x-2 x MIC], LEVX, MOFX, CIPX and OFLX [1x-4 x MIC], RIF [2x-4 x MIC], ERY and AZI [2x-8 x MIC]. TRFX, RIF, LEVX, MOFX, CIPX, OFLX, ERY and AZI showed similar activity against Legionella species other than L. pneumophila. One-hour exposures to the study antimicrobial agents at a concentration of 4 x MIC resulted in PAEs as follows (average in hours): TRFX: 2.68 h; RIF: 2.63 h; CIPX: 2.62 h; MOFX: 2.56 h; LEVX: 2.41 h; OFLX: 2.25 h; AZI: 1.65 h; and ERY: 1.54 h. In conclusion, our in vitro data confirm that trovafloxacin, levofloxacin, moxifloxacin and rifampicin have excellent bacteriostatic and bactericidal activity against Legionella spp and show significant post-antibiotic effect.